Session 2Pollutants and nutrientsin sludge and theireffects on soil, vegetationand fauna

Endocrine disrupters - A general outline of the problem

Peter PärtEuropean Commission-Joint Research Centre, I-21020 Ispra, Italy

Background

The concept of endocrine disruption was first introduced in the 1970s, but publicconcern has since then grown, particularly stimulated by the publication in 1996 ofOur Stolen Future. This book is a digest of the scientific research into endocrinedisruption written for the lay reader, which argued forcefully that endocrine disruptingchemicals are responsible for increasingly common reproductive and behaviouralproblems in humans and wildlife.

The endocrine system co-ordinates the activities of the organs in the body. Endocrineorgans, such as the testes, ovaries, adrenal, pancreas, pituitary, thyroid andparathyroid, produce and release hormones to the bloodstream. Hormones are presentin extremely low concentrations and they act in target organs through highly specificreceptor-mediated systems. Over the last thirty years, evidence has accumulated thata variety of chemicals, including natural and synthetic hormones (alsophytoestrogens), pesticides, additives used by the plastic industry, surfactants andpersistent environmental pollutants like polychlorinated aromatic hydrocarbons (e.g.PCBs and dioxins) can have hormone-like effects. These types of substances havebeen denominated endocrine disrupters (EDs).

The International Programme for Chemical Safety (IPCS - which involves WHO,UNEP and ILO) has, together with Japanese, USA, Canadian, OECD and EuropeanUnion experts, agreed the following working definitions for endocrine disrupters:• A potential endocrine disrupter is an exogenous substance or mixture that possesses

properties that might be expected to lead to endocrine disruption in an intactorganism, or its progeny, or (sub)populations.

• An endocrine disrupter is an exogenous substance or mixture that alters function(s)of the endocrine system and consequently causes adverse health effects in an intactorganism, or its progeny, or (sub)populations.

There are two classes of substances which can cause endocrine disruption:• ‘Natural’ hormones which include oestrogen, progesterone and testosterone found

naturally in the body of humans and animals, and phytoestrogens, substancescontained in some plants such as alfalfa sprouts and soya beans which displayoestrogen-like activity when ingested by the body;

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• Man-made substances which include– Synthetically-produced hormones, including those hormones which are identical

to natural hormones, such as oral contraceptives, hormone replacement treatmentand some animal feed additives, which have been designed intentionally tointerfere with and modulate the endocrine system; and

– Man-made chemicals designed for uses in industry such as in some industrialcleaning agents, in agriculture such as in some pesticides, and in consumer goodssuch as in some plastic additives. It also includes chemicals produced as a by-product of industrial processes such as dioxins, which are suspected of interferingwith the endocrine systems of humans and wildlife.

Plants containing ‘natural’ hormones, such as phytoestrogen, have been shown tohave some beneficial effects on human health such as in the prevention ofcardiovascular diseases, osteoporosis and some cancers. It is believed that the humanbody is able to easily break down and readily excrete these ‘natural’ substances. Thismeans that they spend very little time inside the body and do not accumulate graduallyin body tissue, which is the case with certain man-made substances. There mayhowever be risks associated with changes in lifestyle and altered food and consumerhabits, leading to higher intakes of food containing these substances.

Synthetically-produced hormones are substances which are produced and designed bymanufacturers to ensure specifically that they interfere with and modulate theendocrine system. Dose-response relationships are measured and manufacturers arerequired to publish any available information on the possible side effects of use ofthese substances. The public is frequently in a position to inform itself of the benefitsand possible risks before deciding to avail of these substances. There may, however,be risks associated with direct or indirect exposure, leading, for instance, to theunintended uptake of these substances by non-target populations such as the presenceof synthetic hormone residues in food or in sewage effluent.

Man-made chemicals. There are today approximately 20,000 existing chemicals and200 new chemicals in use (in amounts of more than 1 ton/year) on the EU market.They are designed for use in industry, agriculture and consumer goods and which,apart from the uses for which they were designed, may have unforeseen adverse orsynergistic effects. None of these have in fact been tested for endocrine-disruptingactivity because the necessary testing methods do not exist. Therefore one discusses touse a precautionary approach for regulatory purposes.

Effects and sources of exposure

The phenomenon of endocrine disruption (ED) itself is not new. In 1938 DES(diethylstilbestrol) was designed as a drug to prevent miscarriages in women and tostimulate growth in cattle. In the 1970s/1980s, it was shown to cause severe problemsto male and female reproductive systems, including congenital abnormalities andcancer. It is the first documented example of a chemical which, when given to themother, can cause cancer in her daughter.

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Apart from the example of DES, suspected ED chemicals have been considered to bepotentially involved in a range of human and animal health-related effects. TheScientific Committee on Toxicity, Ecotoxicity and the Environment (SCTEE) of theCommission, has, in its Opinion of 4 March 1999, conducted a review of the existingliterature and scientific opinion on the evidence for chemically-induced endocrinedisruption. It concludes that for human health effects “there are associations betweenendocrine disrupting chemicals, so far investigated, and human health disturbances”such as testicular, breast and prostate cancers, decline in sperm counts, deformities ofthe reproductive organs, thyroid dysfunction as well as intelligence and neurologicalproblems. However, a causative role has not been verified.

For wildlife effects, the Committee concludes that “there is strong evidence obtainedfrom laboratory studies showing the potential of several environmental chemicals tocause endocrine disruption at environmentally realistic exposure levels” and that“although most observed effects currently reported concern heavily polluted areas,there is a potential global problem”.

Impaired reproduction and development causally linked to endocrine disruptingchemicals are well documented in a number of species and have caused local orregional population changes. These include:• masculinization (imposex) in female marine snails by tributyltin (TBT), a biocide

used in anti-fouling paints, is probably the clearest case of endocrine disruptioncaused by an environmental chemical. The dogwhelk is particularly sensitive andimposex has resulted in decline or extinction of local populations world-wide,including coastal areas all over Europe and the open North Sea.

• DDE-induced egg-shell thinning in birds is probably the best example ofreproductive impairment that caused severe population declines in a number ofraptor species in Europe and North America. Developmental exposure to the DDTcomplex has been firmly linked to the induction of ovotestis in male Western gulls.

• Endocrine disrupting chemicals have adversely affected a variety of fish species. Inthe vicinity of certain sources (e.g. effluents of water treatment plants) and in themost contaminated areas this exposure is causally linked with effects onreproductive organs, which could have implications for fish populations. However,there is also a more widespread occurrence of endocrine disruption in fish in theUnited Kingdom, where estrogenic effects have been demonstrated in freshwatersystems, in estuaries and in coastal areas.

• In mammals, the best evidence comes from the field studies on Baltic grey andringed seals and from the semi-field studies on Wadden Sea harbour seals, whereboth reproduction and immune functions have been impaired by PCBs in the foodchain. Reproduction effects resulted in population declines, whereas suppression ofimmune functions has likely contributed to the mass mortalities due to morbillivirusinfections.

• Distorted sex organ development and function in alligators has been related to amajor pesticide spill into a lake in Florida, USA The observed estrogenic/anti-androgenic effects in this reptile have been causally linked in experimental studieswith alligator eggs to the DDT complex.

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For terrestrial (land-living) wildlife, including aquatic mammals, exposure isprimarily expected to be of dietary origin. The situation is different for aquaticwildlife where direct uptake of dissolved chemicals from the water is a significantroute of exposure. Additionally, the reproductive cycle of aquatic organisms with anunprotected embryonic and early life stage development occurring in the freeenvironment makes them particularly susceptible to chemicals in the water.

For humans, possible pathways of exposure to endocrine disrupters include directexposure via the workplace or via consumer products such as food, certain plastics,paints, detergents, cosmetics as well as indirect exposure via the environment (air,water, soil).

In general, the vulnerability of a given species will depend on the intrinsic propertiesof the chemical, on the magnitude, duration, frequency and route of exposure and onthe way in which a given species can absorb, distribute, transform and eliminatesubstances. It will also depend on the sensitivity of specific organs at different stagesof development.

Community strategy on endocrine disrupters

In December 1999 the Commission presented the Community Strategy on EndocrineDisrupters (COM(1999)706 final). The Council Resolution (Council-Environment,press 91, Nr: 7352/00, 30/3/2000) as well as the European Parliament (EP ResolutionA4-0281/98) outline a number of actions, precautions and priorities for the EU in thearea of EDs. Four key elements are identified on the basis of which an appropriate setof actions is recommended. These are:• the need for further research;• the need for international co-ordination;• the need for communication to the public;• the need for policy action.

The first priority of the Community strategy on EDs is to produce a list of prioritychemicals with suspected ED activity to be considered for regulatory actions. Theestablishment of this list is managed by DG Environment.

The research priorities identified by the above mentioned documents can besummarised as follows: • Development and validation of test methods for the identification of ED activity of

industrial chemicals (classification and labelling);• Development of classification criteria for EDs (i.e. whether a substance is an ED or

not);• Understanding of the mechanism of action of the endocrine system, and the range of

effects, including the role of hormones at key stages of life cycles;• Links between adverse health effects in humans and wildlife and exposure to

specific substances, mixtures of EDs, or of mixed exposure to EDs from different

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sources (real life exposure situations) including the health consequences ofphytoestrogens and hormones used as growth promoters;

• Development and validation of environmental monitoring tools;• Refinement of current risk assessment methodologies to address EDs

Endocrine disrupters in the context of waste water treatment and re-use of sewage sludge

There is today compelling evidence that aquatic organisms downstream sewagetreatment plants show signs of endocrine disruption. The symptoms generallycomprise reproductive disorders. However, the ecological consequences with respectto population recruitment, have not been established. General declines in fishpopulations have been reported from several European areas both in fresh and inmarine or brackish water environments but the connection to a possible endocrinedisruption is weak or even non-existing. This area is currently the focus of intensiveresearch, both at national level and within the EU 5th Framework Program.

The substances in wastewater shown to give an endocrine response in fish have partlybeen characterised. They comprise natural or artificial hormones like estrogen andestrogen metabolites, pharmaceutical estrogen analogs like etinyl-estradiol, andchemicals like nonylphenol and bisphenol A. Several studies have shown that fishdown-stream sewage treatment plants actually are exposed for these substances asindicated by metabolites found in the bile. The same fish show an induction of theprotein vitellogenin. Vitellogenin synthesis is controlled by estrogen and vitellogenininduction is a biomarker for exposure to estrogenic compounds. Current studies alsoshow that nonylphenol in concentrations present in the environment downstreamwastewater treatment plants stimulate vitellogenin induction in fish in laboratorystudies. Another chemical shown to induce vitellogenin is bisphenol A. The problemof evaluating the impact of wastewater on aquatic populations is that sewagetreatment effluents contains a mixture of several hormone active substances and it isthe total charge of this mixture that leads to the observed effects. It is not relevantfrom an environmental protection point of view to take regulatory action on singlecompounds in wastewater but it is the total impact of the mixture that has to beconsidered.

Many persistent organic pollutants like PCBs, dioxins and pesticides (DDT) areknown endocrine disrupters and they are, because of their physico-chemical properties(low water solubility), accumulated in the sewage sludge. Re-use of sludge may leadto a re-circulation of these persistent compounds to human food items and to animalfeed. Persistent pollutants are already covered by a number of EC Directives andRegulations because of their general toxicological properties. Their potentiality asEDs does not warrant additional regulatory activity. Still unknown today is to whatextent natural hormones (estrogens) and pharmaceutical residues are accumulated insewage sludge and what happens with these compounds when the sludge is re-used.This is an area the certainly warrants more research in the future.

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References

Community Strategy for Endocrine Disrupters - a range of substances suspected of interfering withhormone systems in humans and wildlife. COM(1999)706, 17 December 1999.

Endocrine Disrupters - Council conclusions. Council of the European Union - Environment, PressRelease - Press: 91, Nr: 07352/00, 30 March 2000.

Opinion on Human and Wildlife Health Effects of Endocrine Disrupting Chemicals, with Emphasison Wildlife and Ecotoxicology Test Methods. Expressed at the 8th CSTEE (Scientific Committee onToxicity, Ecotoxicity and the Environment) plenary meeting, Brussels, 4 March 1999 (DG Healthand Consumer Protection).

T. Colborn, D. Dumanoski and J.P. Myers. Our Stolen Future, Dutton 1996.

Limit values for heavy metal concentrations in sewagesludge and soil that protect soil microorganisms

Ernst WitterDepartment of Soil Sciences, Swedish University of Agricultural SciencesS-7507 Uppsala

Current Council Directive

One of the aims of the current Council Directive of 12 June 1986 on the protection ofthe environment, and in particular of the soil, when sewage sludge is used inagriculture is to regulate the use of sewage sludge in agriculture in such a way as toprevent harmful effects on soil, vegetation, animals and man (Commission of theEuropean Communities, 1986). The Directive restricts metal contamination of soilsthrough:• Limit values for concentrations of heavy metals in soils;• Limit values for heavy metal concentrations in sewage sludge;• Limit values for annual metal loading rates.

According to the text in the Directive the main aim of the limit values for soil metalconcentrations is to avoid toxicity to plants and man. The purpose of the limit valuesfor sludge and for annual metal loading rates is to ensure that the soil concentrationswill not be exceeded as a result of sewage sludge applications (Commission of theEuropean Communities, 1986). In order to fulfil its aims the Directive thereforeheavily relies on the existence of maximum soil (threshold) concentrations ofpotentially toxic heavy metals below which no harmful effects occur.

Since the publication of the Directive a considerable amount of evidence has come tolight about the adverse effects of elevated heavy metal concentrations on soilmicroorganisms. This evidence comes from long-term field experiments where theelevated concentrations have been the result of applications of sewage sludge(sometimes with additional amendments of heavy metals). There is evidence ofseriously adverse effects on agronomically important microorganisms such asrhizobia at, for some metals, soil metal concentrations below the upper limit values inthe Directive (for review see Giller et al., 1998). The rate of sewage sludge applicationin these experiments and the concentrations of metals in the sludge were often greaterthan those allowed under the current Directive. We have, however, no reason tobelieve that the effects on soil microorganisms seen in these experiments should notoccur if soil metal concentrations were allowed to increase to similar levels but at aslower rate as would be the case under the Directive guidelines.

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Evidence of metal toxicity to soil microorganisms

Early evidence of the toxicity of heavy metals to soil microorganisms dates to thebeginning of the 20th century. Much research on this topic since then has concentratedon finding microbial assays for metal toxicity, and on establishing the relative toxicityof a large number of heavy metals. Most of this research has been in the form ofrelatively short-term laboratory studies, where effects are measured at some timeinterval after the addition of metal salts to soil. A compilation of results from thesestudies shows a wide disparity as to at which metal concentrations toxic effects occur(Bååth, 1989; Giller et al., 1998). An emphasis on obtaining quantitative relationshipsbetween soil metal concentrations and toxicity effects in such studies, appears to havebeen at the expense of studies aimed at understanding the complex response of the soilmicrobial community to metal toxicity. Without such an understanding it has provendifficult to interpret the disparity between the different laboratory studies, andmoreover we do not know if, or how, we can extrapolate the effects seen in laboratorystudies to effects that may occur under field conditions.

It has often been assumed that the addition of relatively large amounts of heavy metalsin the form of soluble metal salts in laboratory studies meant that laboratory studiesprovide a worse-case scenario of metal toxicity, compared to the field situation wheresoil metal concentrations increase slowly over a time-span of years, and where themetals are often added in less soluble forms, for example adsorbed to organic matterin sewage sludge. Recent evidence, however, has revealed metal toxicity effects underfield conditions that may occur even at surprisingly low concentrations (e.g. Dahlin etal., 1997). A possible reason why metal toxicity effects are sometimes observed atsuch low metal concentrations under field conditions is that elevated soil metalconcentrations in the long-term may result in changes in the structure and diversity ofthe soil microbial community. Such effects will be overlooked in short-term metaltoxicity studies. An example that illustrates the long-term effect of metal toxicity onthe soil microbial community is the loss of diversity in Rhizobium as a result of pastsewage sludge applications which resulted in the survival of only one strain ofRhizobium in the metal contaminated soil (Giller et al., 1989). This strain happened tobe ineffective in N2-fixation in white clover which was how the effect was noticed inthe first place (McGrath, 1994). The loss of N2-fixation in white clover was thereforenot due to a direct toxicity effect on the ability of the legume/Rhizobium symbiosis tofix dinitrogen, but due to metal toxicity exerting a stress on the population of rhizobia,which eventually led to the survival of only one strain of Rhizobium leg.

These observations led us to hypothesize that:• Metal toxicity exerts a selective pressure on soil micro-organisms thus changing the

relative competitive advantage between microbial groups;• This results in changes in microbial community structure and in the diversity of soil

microorganisms;• These “unseen” effects precede and are the cause of most of the more visible effects

seen at the functional level.

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These hypotheses formed the basis for a recently completed EC-financed study(Giller, 1998) which had as objective to determine the effects of metal contaminationas a result of long term sewage sludge application on the diversity and selectedfunctions of the soil microbial community as well as the diversity of specificmicrobial groups. The study was carried out on soils from the long-term sewagesludge experiment at the Federal Research Centre of Agriculture (FAL) atBraunschweig, Germany. In this experiment either unamended or metal amendedsewage sludge had been applied annually between 1980 and 1989 at two differentrates, resulting in a gradient of soil heavy metal concentrations across the treatments,with the highest metal concentrations around the upper limit values in the Directive.The results from this study showed that there was a change in the structure anddiversity in both broad and narrow subsets of the soil microbial community and anincrease in metal tolerance (Figs. 1-3).

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Figure 1: Diversity and tolerance to Zn of the soil bacterial community and structure of theentire soil microbial community in relation to soil metal concentrations (indicated by soil Znconcentrations). Vertical lines indicate the upper and lower limit values for Zn concentrations insoil according to the Directive. The soil with the lowest soil Zn concentration represents thecontrol (N-fertilized) soil, higher Zn concentrations were due to annual applications ofunamended or metal amended sewage sludge between 1980 and 1989. Soil samples fordetermination of soil microbial characteristics were taken between 1994 and 1996. Soil pHranged from 7.3 to 6.0 and the soil C content from 0.9 to 1.6% with increasing rates of sludgeapplication.Diversity of the soil bacterial community was determined by DNA re-association kinetics, andis here expressed as a % of the bacterial diversity in the control soil. Tolerance to Zn wasdetermined as inhibition of the rate of thymidine incorporation when soil bacteria werechallenged with Zn. Analysis of phospholipid fatty acid patterns (PLFA) was used to assess thecomposition of the soil microbial community and the results shown are the factor scores of thefirst principal component obtained by principal component analysis of the PLFA data.Data from Sandaa et al. (1999) and Witter et al. (2000).

The results shown in Figures 1-3 show that the change in soil microbial communitystructure due to increasing soil metal concentrations was associated with a loss ofdiversity at the highest metal loads, whereas at lower metal loads diversity couldeither increase or decrease. The increase in metal tolerance with increasing metal loadmakes it likely that these changes in community structure and diversity was due to astress exerted by the increased metal concentrations in the soil. Moreover, thetolerance measurements were able to identify that Zn (and possibly Cd) exerted agreater toxicity effect than Cu in these soils (Witter et al., 2000).

It is difficult to assess the consequences of the observed changes in microbialcommunity structure and diversity for functions of the soil microorganisms. Thereexists no general relationship between microbial community structure, diversity andfunction. Moreover, whether or not there is functional redundancy in the soilmicrobial community remains an unresolved issue. In strict Darwinian terms no two

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Figure 2: Catabolic versatility of soil bacterial isolates (mainly Gram positive) measured as thenumber of aromatic substrates that could be used as C and energy source by the isolate. A totalof approximately 150 isolates were tested from each soil using 21 different substrates. Theresults shown are the average number of substrates used by the isolates, expressed as apercentage of the number of substrates used by the isolates obtained from the control soil.Tolerance to Zn was measured in situ as the degree of inhibition of the specific microbialgrowth rate caused by a challenge with Zn added during the exponential growth phase, usingglucose as substrate and is expressed as a percentage of microbial tolerance to Zn in the controlsoil. The “community structure” of the microbial community able to use 15 different Csubstrates in situ was determined by principal component analysis of the specific microbialgrowth rates for these substrates.For more details of the soils see the legend for Figure 1.Data from Wenderoth and Reber (1999) and Witter et al. (2000).

species with exactly the same characteristics can co-exist in the same ecosystem,unless physically isolated in time or space. In the case of the metal contaminated soilsof the experiment at Braunschweig the loss of catabolic versatility observed inindividual isolates did in no instance result in the complete loss of a cataboliccapability from the soil microbial community. Clearly, under the experimentalconditions under which the catabolic capabilities were assessed there wasconsiderable functional redundancy. In how far there appears to be redundancy for agiven function is of course entirely dependent on the function and the conditionsunder which the function needs to be expressed. The ability to metabolise simplecarbohydrates, for example, will have a large degree of functional redundancy,whereas there will only be limited redundancy for the ability to degrade complexorganic molecules such as lignin, or PCBs and other difficult to degrade xenobiotics.It is, however, likely that species with partially or even entirely similar cataboliccapabilities will differ in some other characteristic that would ensure the survival ofall species. For a highly specialised function such a symbiotic dinitrogen fixation thedegree of apparent redundancy is likely to be much smaller. Loss of diversity in thisgroup of microorganisms can therefore be expected to more likely result in the loss ofa common function, as was shown in the loss of R. leguminosarum bv. trifolii

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Figure 3: Numbers of Rhizobium leguminosarum bv. viciae, number of plasmids per isolateand the total number of plasmid groups found in the isolates of R. leguminosarum. The numberof rhizobia was measured by the most probable number plant infection technique. The numberof plasmid groups – based on the number plasmid profiles found - in each population is used asa measure of the diversity in R. leguminosarum. The number of plasmids carried by isolates wasassociated with increased metal tolerance, but there was only a weak tendency of increasedtolerance to Zn with increasing soil metal concentrations.For more details of the soils see the legend for Figure 1.Data from Lakzian et al. (1999).

effective in dinitrogen fixation in white clover in the sludge amended soil from theWoburn experiment due to the survival of only one strain (Giller et al., 1989). In theBraunschweig experiment loss of diversity in the rhizobia bacteria was seen at thehigher metal loads, but no loss of dinitrogen fixing ability was found. In contrast, insome of the most contaminated plots (with soil metal concentrations around the upperlimit values in the Directive) R. leguminosarum bv. trifolii was completely absent,with obvious consequences for crop plants relying on this bacterium for symbioticdinitrogen fixation (although this loss in practice can be overcome by inoculation ofseeds).

Implications for limit values for soil and sewage sludge

Despite the difficulties in establishing relationships between microbial diversity andfunction, the loss of diversity must in general be seen as an undesirable effect, becauseof the potential loss of microbial functions that this implies. When assessing thegravity of a given effect on soil microorganisms, the extent of the effect must be put inrelation to the reversibility and duration of the effect. Soil cultivation, choice of crops,and numerous other standard agronomic practices can have effects on soilmicroorganisms that may be even more severe than some of the effects we have seenat moderate levels of metal contamination in the Braunschweig experiment. Theseeffects are, however, by and large entirely reversible and of short duration. This is instark contrast to the effects caused by the toxicity effect exerted by heavy metals insoil. Heavy metals have a persistency in agricultural soils in the order of manythousands of years (McGrath, 1987), which is a compelling argument for adopting aprecautionary approach in regulations concerning metal contamination of agriculturalsoils (Witter, 1996). In terms of the EU Directive on the agricultural use of sewagesludge, a precautionary approach would be reflected in the annual metal loading limits(i.e. limit values that regulate the rate at which heavy metals are allowed toaccumulate in the soil) and in the limit values for heavy metal concentrations in soil.In the current Directive the former limits are set extremely high, and are essentiallyredundant as for most metals the average metal concentrations in municipal sewagesludge in EU member states are considerably below the limit values (Commission ofthe European Communities, 2000). A precautionary approach to limit values forannual metal loading rates would try to set these limits as low as practically possiblewith a view to successively reduce loading rates until a situation of near “zero-accumulation” of metals in soils is achieved, at least for the potentially most toxicmetals. A precautionary approach to limit values for soil metal concentrations mightwant to set limit values as low as practically possible, and at least belowconcentrations known to result in adverse effects. In practice this is, however, difficultto achieve. There is a large natural variation in soil metal concentrations making itdifficult to establish metal concentrations that will identify metal polluted soils. Theevidence for soil metal concentrations that can be associated with no adverse effectson soil microorganisms is incomplete, and there is also some doubt whether there areclear threshold soil metal concentrations below which there are no adverse effects.

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The evidence from the Braunschweig experiment on the effects of elevated soil metalconcentrations on the number of rhizobia suggest that there may be a threshold value,which for Zn would be in the range of 150-250 mg kg-1 (Chaudri et al., 1993). Someof the evidence from the Braunschweig experiment reviewed here (Figs. 1-3),however, suggests that soil microorganisms may already become affected at low metalloading rates, with no evidence of threshold concentrations. This issue will remaindifficult to resolve, not least because of the difficulties in establishing statisticallysignificant effects on biological parameters with a large inherent variability.

Conclusions

• Evidence from long-term field experiments show that heavy metals impair bothmicrobial diversity and function in soils;

• Changes in microbial community structure and diversity often occur beforefunctions are affected;

• The upper limit values for soil metal concentrations in the current Directiveinsufficiently protect soil micro-organisms and important functions, and do notmeet criteria for a sustainable management of agricultural soils;

• There is insufficient evidence to set limits for soil metal concentrations that canguarantee to avoid adverse effects on soil microorganisms;

• The current Directive allows a rapid accumulation of metals in soils;• Such accumulation is essentially irreversible;• A new Directive should encompass a precautionary approach and put more

emphasis on minimising metal accumulation in soils.

References

Bååth E. (1989) Effects of heavy metals in soil on microbial processes and populations (a review).Water, Air, & Soil Pollution 47, 335-379.

Chaudri A.M., McGrath S.P., Giller K.E., Rietz E. and Sauerbeck D.R. (1993) Enumeration ofindigenous Rhizobium leguminosarum biovar trifolii in soils previously treated with metal-contaminated sewage sludge. Soil Biology & Biochemistry 25, 301-309.

Commission of the European Communities (1986) Council Directive of 12 June 1986 on theprotection of the environment, and in particular of the soil, when sewage sludge is used in agriculture.Official Journal of the European Communities L181 (86/278/EEC), 6-12 OJ L181, 4.7.86.

Commission of the European Communities (2000) Report from the Commission to the Council andthe European Parliament on the implementation of Community waste legislation for the period 1995-1997. COM(1999) 752 final, 1-92.

Dahlin S., Witter E., Mårtensson A.M., Turner A. and Bååth E. (1997) Where's the limit? Changes inthe microbiological properties of agricultural soils at low levels of metal contamination. Soil Biology& Biochemistry 29, 1405-1415.

Giller K.E. (1998) Microbila diversity and function in metal contaminated soils. Final report.Contract Number EV5V-0415.

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Giller K.E., McGrath S.P. and Hirsch P.R. (1989) Absence of nitrogen fixation in clover grown onsoil subject to long term contamination with heavy metals is due to survival of only ineffectiveRhizobium. Soil Biology & Biochemistry 21, 841-848.

Giller K.E., Witter E. and McGrath S.P. (1998) Toxicity of heavy metals to microorganisms andmicrobial processes in agricultural soils: A review. Soil Biology & Biochemistry 30, 1389-1414.

Lakzian A., Murphy P., Turner A., Beynon J.L. and Giller K.E. (1999) Abundance, plasmid profiles,diversity and metal tolerance of Rhizobium leguminosarum bv. viciae populations in soils withincreasing heavy metal contamination. Unpublished.

McGrath S.P. (1987) Long term studies of metal transfers following application of sewage sludge. InPollutant transport and fate in ecosystems. Vol 6 (P.J. Coughtrey, M.H. Martin and M.H. Unsworth,Eds), pp. 301-317. British Ecological Society, London.

McGrath S.P. (1994) Effects of heavy metals from sewage sludge on soil microbes in agriculturalecosystems. In Toxic metals in soil-plant systems (S.M. Ross, Ed), pp. 247-274. John Wiley & Sons,Chichester, UK.

Sandaa R.A., Torsvik V., Enger O., Daae F.L., Castberg T. and Hahn D. (1999) Analysis of bacterialcommunities in heavy metal-contaminated soils at different levels of resolution. FEMS MicrobiologyEcology 30, 237-251.

Wenderoth D.F. and Reber H.H. (1999) Correlation between structural diversity and catabolicversatility of metal-affected prototrophic bacteria. in soil. Soil Biology & Biochemistry 31, 345-352.

Witter E. (1996) Towards zero accumulation of heavy metals in soils: an imperative or a fad?Fertilizer Research 43, 225-233.

Witter E., Gong P., Baath E. and Marstorp H. (2000) A study of the structure and metal tolerance ofthe soil microbial community 6 years after cessation of sewage sludge applications. EnvironmentalToxicology and Chemistry (In Press).

Persistent organic pollutants and metals from sewage sludges: their effects on soil, plants and the food chain

S.P. McGrathIACR-Rothamsted, Harpenden, Herts AL5 2JQ, UK.

Introduction

It is not the purpose of this chapter to report a complete review of the literature on thesubject. Rather, the aim is to bring together information on the risks of certain groupsof organic pollutants and potentially toxic metals, focusing on results from long-termexperiments, particularly in the UK and Germany.

Experiments utilised

A key issue is the length of experiments. In order to give stable results, theexperiments have to be well-equilibrated and therefore long-term in nature. Apartfrom the standard statistical considerations of design and replication, they must alsocontain control plots, which are essential for the interpretation of the results. A shortdescription of each of the experiments is given below.

Woburn, England: Twenty five applications of anaerobically digested sewage sludge,naturally contaminated with metals, from a sewage works in West London were addedat 37.5 or 75 t fresh weight of sludge ha-1 from 1942-1961. In addition, two types ofcontrol plots were established on this experiment: farmyard manure (FYM) at 37.5 or75 t fresh weight ha-1; and inorganic fertilizer. Since 1961 and 1965, respectively, thesewage sludge and FYM treatments have received only inorganic fertilizers. The soilis a sandy loam with about 10% clay and 2% organic carbon. The pH has beenmaintained around 6.5 by regular maintenance dressings of lime.

Lee Valley, Luddington and Rosemaund Frame Experiments, England: The soil at LeeValley is a heavy silt loam with 21% clay, 4% organic carbon and a pH of 5.6-5.9. Thatat Luddington is a sandy loam with 15% clay, 3% organic carbon and a pH of 6.0.Sewage sludges from various sewage works were used and the different treatmentsreceived either a single large dose of 125 t dry solids (DS) ha-1 of four sewage sludgescontaminated predominately with Zn (16000 mg kg-1), Cu (8000 mg kg-1), Ni (4000 mgkg-1), or Cr (8000 mg kg-1), or 31 t ha-1 yr-1 of the same sludges for four years from 1968.In addition, there was a relatively uncontaminated sludge treatment and a control

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treatment with inorganic fertilizers only. The plots at Luddington were excavated in1991 and transferred to wooden frames 1.2 m x 1.2 m square and 12 cm deep atRosemaund farm. The treated soils now overlie the native soil, which is a silty clay loam.

Gleadthorpe, England: The soil at this site is a sandy loam with 9% clay and 1-2%organic carbon (control soil). This experiment was started in 1982. The sewagesludges used were artificially contaminated by adding metal salts to raw sewage andthen dewatering. One application of Zn or Cu or Ni-contaminated sludge was made toall plots with a further application to some, but not all, 5 years later. Apart from thesesingle metal treatments, mixed metal treatments of Zn plus Cu and Zn plus Ni werealso applied. There were also treatments with 100 t DS ha-1 ‘uncontaminated’ sewagesludge in 1982, or inorganic fertilizers.

Braunschweig, Germany: Two field experiments were begun in 1980 on the same fieldand both received the same treatments consisting of inorganic fertilizers or ‘moderately’contaminated or metal-amended liquid sludge added at the equivalent 5 or 16 t DS ha-1

yr-1 from 1980-1990. The moderately contaminated sewage sludges used were obtainedfrom a local sewage works and were naturally contaminated. However, the‘contaminated’ sludge was from a different works in 1980, then from 1981-1990 thesame moderately contaminated sludge was artificially amended with metal salts andanaerobically incubated for six weeks before use. One experimental site (Braunschweig1) was on an old arable soil with plot pH values ranging from 6.0-7.0 and 0.8-1.5%organic carbon content; the other experimental site (Braunschweig 2) was on an ex-woodland soil with plot pH values ranging from 5.3-5.7 and 1.6-2.6% organic carboncontent. Both soils are silty loams with 50% silt, 45% sand and 5% clay.

Persistent Organic Pollutants (POPs)

There are a large number of POPs that occur in sewage and these can persist throughtreatment processes such as anaerobic digestion, and then build up in soils to whichsewage sludges are applied. On the whole, the persistent compounds are quitehydrophobic and they bind to soil organic matter, however, there is a large range bothhydrophobicity, and the volatility, of the compounds involved.

The aims of the work reported in this section are:• To measure the inputs and losses of POPs in long-term sewage sludge experiments;• Evaluate their movement to water;• Evaluate their movement into crops;• Measure their effects on soil microbial populations.

Inputs and losses of POPs

PAHs

Soil samples archived from the 0-23 cm layer of a control (inorganic) treatment and aplot that had received the highest rate of sewage sludge in the Woburn Market GardenExperiment were retrospectively analysed for the PAH compounds shown in Table 2.

The same compounds were determined in the archived sewage sludge samples from1942-61. The sum of the PAH compounds analysed is referred to as ΣPAH. The meanΣPAH concentration in the sludges was 50 mg kg-1, and the total addition was calculatedto be 44 kg ΣPAH ha-1 over the period of sludge additions (Wild et al, 1990a).

Table 1 shows that the concentrations of ΣPAH increased in both the control and sewagesludge-treated plots, however, the increase was greater in the sewage sludge treatments(Wild et al., 1990b). When sewage sludge additions ceased, the concentrations of PAHsin the soil fell gradually. So, in 1960, a year before sludge additions ceased, the ratio ofΣPAH between the sludge treatment and control was 5.6, and by 1984, this had fallen to3.3. There were compound-specific differences in the loss of PAHs, with the lightercompounds being lost more than the heavier ones (Table 2).

From this experiment, it was possible to derive half-lives of 8 sludge-derived PAHsby considering the post-1960 changes (Table 3). For ΣPAH, an exponential decaycurve gave a fitted half-life of about 19 years. Those for individual compounds rangedfrom 8-27 years, increasing with molecular weight (Wild et al, 1990b). The decreasein soil concentrations appears to be due to a combination processes such asvolatilization, biodegradation and transfers out of the treated plots due to ploughing(McGrath and Lane, 1989, Wild et al., 1990b).

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Table 1: Soil PAH concentrations in the Woburn Market Garden Experiment (from Wild et al.,1990b).

PAH concentrations (ΣPAH), mg kg-1 soilTreatment 1942 1951 1960 1967 1972 1980 1984Sludge 216 3804 5527 3872 3117 3131 2427Control 216 473 971 801 503 735 727

Table 2: Enrichment ratios in soils of theWoburn Market Garden Experiment (from Wildet al., 1990b).

Compound 1960 1984napthalene – –acenaphthene/fluorene 1.3 0.26phenanthrene 2.8 0.59anthracene 3.3 1.1fluoranthene 4.7 2.9pyrene 6.1 2.7benzanthracene/chrysene 13 6.8benzo[b]fluoranthene 9.4 5.5benzo[a]pyrene 14 7.0benzo[ghi]perylen 10 4.8ΣPAH 5.6 3.3

Table 3: Field half lives of PAHs in soilsof the Woburn Market Garden Experiment(from Wild et al., 1990b).

Compound Half lifenapthalene –acenaphthene/fluorene –phenanthrene 15anthracene 8fluoranthene 17pyrene 18benzanthracene/chrysene 28benzo[b]fluoranthene 27benzo[a]pyrene 26benzo[ghi]perylene 25ΣPAH 19

PCBs

Archived soils, 0-23 cm deep, from a control and a sludge rate 2 plot of the WoburnMarket Garden Experiment were analysed retrospectively for the following PCBcongeners: 8, 14, 18, 28, 52, 104, 44, 40, 61/72, 66, 101, 99, 110, 82/151, 149, 118,188, 153, 105, 138, 183, 180, 170, 201, 208, 206 and 194/205 (Alcock et al., 1995).

PCB concentrations were also measured in archived sewage sludge samples (1942-1961). The mean ΣPCB concentration in the 24 sludges was 1,570 µg kg-1 withconcentrations varying between 44 and 4,335 µg kg-1. Using the sludge ΣPCBconcentrations and the known dry weights of sludges applied, it was calculated thatthe total amount of PCBs originally added to the Woburn soil was approximately 1 kgof ΣPCB ha-1 over 20 years (Alcock et al., 1995).

In 1942, prior to sludge additions, the soil at Woburn contained about 63 µg ΣPCB kg-1.It was found that the PCB burden of the control plot increased steadily from that time,as a result of atmospheric inputs, to reach a maximum in the 1972 sample of 561 µgΣPCB kg-1 (Table 4). Tri- and tetra-chlorinated congeners (e.g. 18, 28, 52, 66)dominated the composition of the samples at that time; these two groups accounted for>75% of ΣPCB in the 1972 control plot.

The sharp increase in soil ΣPCB levels between the 1940s and the mid-1960scoincided with trends in the industrial manufacture of these chemicals, both in the UKand on a global scale. The ΣPCB levels at Woburn have declined since 1972, and thecontemporary burden (ca. 13 µg ΣPCB kg-1) of ΣPCBs in surface soil at Woburn isactually lower than that found in the 1942 sample. These substantial changes in thePCB concentrations of the control plot mirror those observed in archived samplesfrom other long-term UK agricultural experiments (Alcock et al., 1993).

The trend in the ΣPCB burden of the sludge-amended plots closely followed that ofthe control (Table 4). Air-soil exchanges therefore also clearly exert a strong influenceon the trends in the sludge-amended plot. Concentrations reached a maximum of 817µg ΣPCB kg-1 in 1972, for example, even though sludge was applied only between1942 and 1961. Cessation of the sludge additions did not result in an immediategradual decline in ΣPCB concentrations, as was the case with PAHs in these soils.Concentrations remained relatively constant between 1960 and 1980, then fell sharplyto the present day levels (70 µg ΣPCB kg-1). In 1984 the control plot contained 0.96%organic carbon, while the sludge-amended plot contained 1.99%. By 1992, 31 yearsafter the last sludge was applied, the sludge-amended plot contained over 5 timesmore ΣPCB than did the control plot, over 30 years after the last sludge application.

The lighter congeners (e.g. 28, 52 and 66) also generally dominated the congenercomposition of the sludge-amended plot (Alcock et al., 1995). Trichlorinatedcongeners (e.g. 18 and 28) dominated the congener composition in each sample from1951 to 1984, constituting >30% of the ΣPCB content. However, in the most recentsample (1992) penta-chlorinated congeners (101, 110 and 118) were most abundant.Interestingly, lower molecular weight PCBs only declined in concentration after 1980.Concentrations of congeners 28 and 52, for example, remained relatively constantfrom 1951 to 1972, then declined sharply in the most recent sample. In contrast,

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concentrations of heavier congeners (e.g. 101, 149, 138 and 180) were much lowerfollowing the cessation of sludge additions in 1961, but have remained relativelyconstant since, decreasing only slightly in the most recent sample.

Inputs from the atmosphere appeared to be the dominant influence on the PCB contentof the soil at Woburn, even on the plot to which large applications of sewage sludgewere made. Over and above this, the addition of sewage sludge resulted in an increasein the soil PCB content at Woburn. The decrease in concentration of sludge-derivedPCBs is thought to be due to a combination of processes – volatilisation, transfers outof the experimental plot due to ploughing, and microbial degradation. The rate ofdecline varied between individual compounds, and the higher molecular weight PCBshave generally been more persistent.

Biodegradation of PCBs is likely to be minor, since it has already been establishedthat aerobic degradation is slow, especially for the more recalcitrant congeners.Volatilization losses of 14C-labelled tri-, tetra- and pentachlorinated PCBs from soilscan be substantial and could account for the majority of the compounds lost (Moza etal, 1979). Volatilization fluxes are temperature-dependent and may result in PCBsfrom temperate latitudes, such as the United Kingdom, migrating by ‘coldcondensation’ process to the sub-Arctic and Arctic regions (Jones et al., 1994, 1995),where high concentrations have been observed far from local sources (Oehme, 1991).

Chorobenzenes

Chlorobenzenes (CBs) are a major group of substituted monocyclic aromatics which areubiquitous in sewage sludges. The ΣCB concentrations in UK sewage sludges have beenreported to be from 10 to tens of thousands of µgkg-1 (Wang et al, 1992).Dichlorobenzenes (DCBs), 1,2,4-trichlorobenzenes (1,2,4-TCB), and hexachlorobenzene(HCB) have been classified as priority pollutants by the United States EnvironmentalProtection Agency (US EPA) and by the EU. Some CBs (e.g. HCB) are known humancarcinogens. CBs were therefore measured in the Woburn Market Garden Experiment.

The mean concentration of ΣCBs in sludges applied at Woburn was 67.4 µg kg-1 andthe range 11-327 µg kg-1 (Wang et al, 1995). During the 20-year application period,there were six years (1942, 1947, 1948, 1952, 1954 and 1959) in which the CBaddition was less than 1 g ha-1, while the input of CBs reached more than 6 g ha-1 inanother two years (1943 and 1953). The average load was 2.60 g ha-1 year-1.

Table 4: Soil PCB concentrations in the Woburn Market Garden Experiment (from Alcock etal., 1995).

PCB concentrations (ΣPCB), µg kg-1 soilTreatment 1942 1951 1960 1967 1972 1980 1984 1992Sludge 62.6 178 640 652 817 449 183 70.1Control 62.6 126 465 398 561 271 60.4 12.7

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The concentrations of individual CBs in both control and sludge-amended soil werevery low, i.e. less than 1 mg kg-1, except for 1,4-DCB. The concentrations of CBs inthe control soil remained relatively stable for the 50 years, with the exception of 1,4-DCB which showed a sharp increase in the 1960s. When sludge was being applied,the concentrations of all the CBs in the sludge-amended soil increased and remainedhigher than those in the control plot after sludge applications ceased. This indicatedthat multiple sewage sludge applications increased the concentrations of CBs in soil tolevels which remained detectable for at least a period of 30 years. However, the CBconcentrations in the sludge-amended soil were still lower than the means of CBs inthe surface soils collected from areas where industrial plant and combustion sourcesare potential pollution sources (Wang et al., 1995).

By the time of sampling in 1951 and 1960, much of the CBs in sewage sludge addedto the soil had already disappeared (Wang et al., 1995). The residues left in the soilappeared to be very persistent and were basically not removed further in the following30 years. The concentration of HCB continued decreasing between 1960 and 1967,showing that this compound was significantly more persistent than the other CBs, thelosses of which had basically finished before these samples were collected. Excluding1,4-DCB, about 10% of the ΣCBs applied originally were still in the soil 30 years aftersludge applications stopped (Table 5).

Following sewage sludge applications, CB loss processes can occur simultaneously.Possible fates include volatilization, abiotic and biological degradation, erosion,leaching and plant uptake. Although crop offtake could be important in relation topotential human exposure, the proportion of CBs lost due to plant uptake is smallcompared with the total amount lost. Volatilization was highlighted as the main fate ofCBs in the soils (Wang and Jones, 1994). The difference between the persistence ofdifferent CBs in the soil supports this idea, i.e. compounds like 1,2-DCB with a highervapour pressure and Henry's constant tend to volatilize and show smaller residualconcentrations in soil than compounds like HCB with lower volatility.

Polychlorinated dibenzo-p-dioxins and furans

PCDD/Fs and non-o-PCBs were determined in 8 digested sewage sludges sampledfrom rural and urban wastewater treatment works in the north-west of England in the

Table 5: Soil CB concentrations minus 1,4-DCB in the Woburn Market Garden Experiment(from Wang et al., 1995).

CB concentrations (ΣCB), mg kg-1 soilTreatment 1942 1951 1960 1967 1972 1980 1984 1991Sludge 0.85 1.34 2.31 2.27 1.76 2.12 2.07 1.50Control 0.85 0.42 0.70 1.07 1.07 1.00 0.79 0.48

1990s. In addition, 7 of the twenty five archived sewage sludge samples collected andstored from a sewage treatment works in West London for application to the WoburnMarket Garden Experiment between 1942 and 1960, were analysed to gain someinsight into temporal trends and possible variations in source inputs (Sewart et al.,1995). Control plots only (fertilizer treatment) were analysed to determine theamounts of dioxins coming from atmospheric deposition.

The total PCDD/F homologue concentrations and the 2, 3, 7, 8-substituted congenersin the archived sludge samples analysed by GC/HRMS are presented as toxicityequivalent values (TEQ, McLaughlin, 1992) in Table 6. The ΣTEQ values in thesamples from 1942-60 are higher than those measured in the contemporary sludges(Table 7). This may reflect a general decline in PCDD/F inputs to the environment,due to tighter controls on organochlorine use and disposal.

Three distinct patterns were noted over time in the ‘signatures’ of congeners in theWoburn sludge samples:a: Tetra and penta CDD/F and HxCDF concentrations remained quite constant

between 1942-1960. Typical source profiles indicate atmospheric inputs i.e.combustion as the major source and these have remained fairly constant over thesampling period.

b: Hexa- to octa-CDD congeners increased by up to a factor of 200 between 1942 and1956, followed by a sharp (60%) decrease in levels over the next 4 years.

c: 1, 2, 3, 4, 7, 8-HxCDD and HpCDF-OCDF congeners increased by up to a factor of20 between 1942 to 1958, subsequently decreasing by 40%.

Patterns b and c were attributed by Sewart et al. (1995) to PCP contamination; PCPand its derivatives are widely used in the wood and textiles industry to prevent fungal/microbial attack.

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Table 7: 2,3,7,8-substituted PCDD/F concentrations in 8 sewage sludge samples in the northwest of England in 1992 (ng kg-1), from Sewart et al., 1995.

Location2 4 7 8 9 10 11 12

ΣTEQ 29 29 23 0.7 9.9 29 15 0.4

Table 6: PCDD/F concentrations in archived sewage sludge from the Isleworth sewage works,West London (ng kg-1), from Sewart et al., 1995.

Year of collection1942 1944 1949 1953 1956 1958 1960

ΣTEQ 18 36 61 127 402 229 166

The concentration of the dioxin 2,3,7,8-TCDD in plots not treated with sewage sludgewas found to increase from 40 pg kg-1 soil from the mid 1940s to 110 pg kg-1 atpresent (K.C. Jones, personal communication). Because these compounds have lowvolatilisation potentials and their susceptibility to degradation is very low, it appearsthat dioxin compounds are accumulating in the soil (Jones et al., 1994, 1995). Theaverage concentration of 2,3,7,8-TCDD measured in the sludges added to the WoburnMarket Garden Experiment was 2,800 pg kg-1 (Sewart et al., 1995). The 25applications of sludge over 20 years added 71 ng kg-1 to the soil in the sludge rate 1treatment, and double this in rate 2. To put the sludge inputs in perspective, after only20 years of sludge addition, they were equivalent to approximately 1000 and 2000times the inputs from the atmosphere in 40 years. The sum of the TEQs for PCDD/Fsin recent sludges was 19-206 ng kg-1, whilst at Woburn it was 18-402. German rulesfrom 1992 prohibit the use of sludge when ΣTEQ is greater than 100 ng kg-1 (GermanFederal Ministry of the Environment, 1992).

There are limited field data on the effects of sludge application on levels of PCDD/Fsand non-o-substituted PCBs in the food chain. Wild et al. (1994) used literature dataand pathway analyses to show that human exposure to PCDD/Fs could potentiallyincrease under some realistic sludge application scenarios.

Movement of POPs into water

Sludge application to land must be sustainable and not cause effects on the food chainor pollution of aquifers. Very little work has been done on the leaching of organiccompounds, as most of the sludge-borne organic pollutants are either transient (i.e.broken down or volatilized from soil before leaching can take place), or are solipophilic that they become bound to soil organic matter in the upper layers and areeffectively immobilised there. However, there is concern about the extent to whichcolloid-facilitated transport of organic pollutants and heavy metals occurs (e.g. Lamy,1993). Nonylphenol is a substance which is persistent, soluble and present in largequantities in sewage sludge (up to 2,500 mg kg-1 DM), and its presence in water hasbeen linked to adverse effects such as sex changes in fish and low sperm count inhumans. This compound was an obvious target for potential mobility.

Intact monolith lysimeters of Woburn soil (80 cm diameter, 1 m deep) were collectedin 1994. They were sown with grass then treated with 0, 100 and 400 m3 of liquidsewage sludge (equivalent to 0, 3 and 12 t DM ha-1) in early 1995. Drainage wascollected in containers after gravity feed. Monitoring of the drainage from each wascontinued throughout the year. Drainage water was solvent extracted and theconcentrations of 4-nonlyphenol were quantified using GC-MS.

The sludge applied was relatively contaminated, containing 430 mg kg-1 DMnonylphenol. The concentrations of nonylphenol in the drainage water were notgreater in the lysimeters with the highest rate of sludge, and did not increase with time(Table 8). These are very small concentrations, and the number of samples belowdetection was great. Effectively, no quantifiable amounts of nonylphenol leachedfrom the soil after the sludge application.

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In contrast, soluble organic carbon, nitrateand chloride were leached from the wholelysimeter depth, i.e. to beyond 1 m. Therewas variation between the lysimeters: therewas typically 15-30 mg l-1 of organiccarbon in the drainage from the 100 and400 m3 treatments, and 5-10 mg l-1 in thecontrols. Nitrate-N and chloride were moretransient, peaking in autumn at 20-70 and7-23 mg l-1 in the high sludge treatment. Incontrast to carbon, the nitrate and chlorideconcentrations in drainage from the 100 m3

treatment were similar to control.

The loss of even as mobile a persistentorganic pollutant as nonylphenol wasnegligible, and it is possible that some ofthat applied was lost by volatilization ordecomposition. However, some organiccompounds not likely to be pollutants wereleached, as shown by the total organiccarbon measurements.

Movement of POPs into crops

Concentrations of PAHs in different crops/crop parts were measured in some archivedcrop materials from the Luddington, Lee Valley and Woburn Market Gardenexperiments (Wild et al., 1992). Increases of PAH concentrations in crops grown onsludge treatments above the appropriate controls were not consistent. Of the crops,carrots showed the highest concentrations, and it is likely that the PAHs in root cropsare mainly due to adsorption to the root surface. In above ground parts, the plantmaterials were relatively enriched with low molecular weight PAHs.

A comparison between the PAH congeners in soil, sludge, air and plants pointed to theatmosphere as the main source of PAHs in aboveground plant parts (Wild et al.,1992). This implies that there is little uptake and transport of PAHs through the plant,and possibly applies to other lipophilic POPs in the soil.

Effects of POPs on soil microbial populations

A ‘worst case scenario’ was designed, in which the largest concentration of eachindividual organic compound reported in sewage sludge was added to soil, but withoutsludge (Chaudri et al., 1996). Ten organic compounds were chosen to represent as widea range of chemical classes as possible and included those thought to present the highestrisk to soil microorganisms (Table 9). To assess the effects of the organic contaminants,a species-specific plant infection test was used to determine the most probable number(MPN) of rhizobia surviving in the treated soils and in untreated controls.

Table 8: Concentrations of nonylphenol inselected lysimeter drainage waters (µg l-1).

Treatment Date NonylphenolNo sludge 22/11/95 <0.2

29/11/95 <0.211/12/95 <0.28/1/96 <0.215/1/96 0.229/2/96 <0.226/2/96 <0.218/3/96 <0.229/3/96 0.28

400 m3 ha-1 22/11/95 <0.229/11/95 <0.211/12/85 <0.28/1/96 <0.215/1/96 <0.226/2/96 <0.218/3/96 <0.229/3/96 <0.2

The compounds were dissolved in either water or methanol prior to addition.Methanol was used to dissolve compounds, which were relatively insoluble in water.Control soils, treated with methanol and water only, were also included to ensure thatthe effects observed on the microorganisms were not due to either of the solventsused. A separate treatment containing 3.55 g glucose kg-1 soil only was also includedto compare the effects of adding a readily available and metabolizable C source withthat from the organic compounds on the numbers of rhizobia.

The MPN method was used to estimate the number of indigenous Rhizobiumleguminosarum bv. trifolii using a 10-fold dilution series and white clover (cv.Blanca) as the trap host. Of the 10 organic compounds assessed, only PCP was toxicto the indigenous population of R. leguminosarum bv. trifolii, with no recovery overtime (Table 10). For example, PCP significantly decreased the population ofindigenous rhizobia (to 2000 cells g-1 soil) at 35 days compared to both the water andmethanol controls. At 77 days no rhizobia could be detected in the PCP-treated soilusing the MPN technique.

The other compounds listed in Table 10 had no or very little effect on the rhizobialpopulation. Possible reasons for this may be: 1) These compounds were added at

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Table 9: Organic compounds chosen, their group properties and concentrations in sewagesludge in mg kg-1 dry wt (after Chaudri et al., 1996).

Group Group properties Compound ConcentrationPolycyclic aromatic Recalcitrant petroleum Anthracene max - 44Hydro-carbons hydrocarbons. High molecular(PAHs) weight. Biocidal.

Origins - dyes, pesticides, fuels and oils

Polychlorinated Highly recalcitrant. Aroclor 1016 0.2-74biphenyls (PCBs) Origins - transformers, plasticsSurfactants Used in soap industry, LAS* max- 12,000

component of washing powders Nonylphenol max-2530Short chained Usually volatile. Used in fire Tetrachloro-ethylene 0.024-42aliphatics extinguishers, refridgerants,

pesticides, solvents etc. Biocidal.

Monocyclic Aromatics Volatile, subject to microbial Ethylbenzene max-51degradation Toluene 0-0.137Origins - explosives, fungicides, herbicides.

Phenols Extremely widespread 2, 4-dichlorophenol max-203 Often recalcitrant. Pentachlorophenol 0.172-8490Often chemical intermediates. Phenol max-288Biocidal

*LAS = linear alkybenezenesulphonate.

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concentrations found in sewage sludge, and may not be high enough to cause toxicity(e.g. anthracene, aroclor 1016, trichloroethylene and 2, 4-dichlorophenol). 2) Theymay have became bound strongly in the soil, further reducing their availability andhence toxicity. 3) They may have been subject to rapid microbial degradation into lesstoxic or harmless compounds (e.g. LAS, ethylbenzene, toluene and phenol). Forexample, LAS is known to be rapidly biodegraded in soil, with a residualconcentration of <10% remaining after 320 days (Marcomini et al, 1989). Similarly,microbial degradation of phenol, toluene and benzene have been reported in soil. 4) Rhizobium leguminosarum bv. trifolii may be tolerant to the organic compoundsand their derivatives.

However, after 6 months, with the exception of the PCP-treated soil, all othertreatments including glucose had rhizobial numbers, which were not significantlydifferent from the control soils (Table 10).

Figure 1 shows the dose-response curve of PCP against rhizobial numbers measuredat 6 months. The lowest observed adverse effect concentration (LOAEC) thatsignificantly decreased the rhizobial population was 120 mg PCP kg-1 soil after 2months, with no rhizobia detected at 200 mg kg-1 soil (data not shown).

At 6 months, the highest no observed adverse effect concentration (HNOAEC)decreased to about 50 mg PCP kg-1 soil and the LOAEC was 75 mg PCP kg-1 soil (no

Table 10: Indigenous numbers of R. leguminosarum bv. trifolii after 5 weeks and 6 months, insoils amended with organic compounds (after Chaudri et al., 1996).

Treatment Conc. added 2Carbon conc. 5 weeks 6 months(mg kg-1) added x103 cells g-1 soil

(mg kg-1)Water Control – – 240 120Methanol Control 10 ml kg-1 2960.00 120 120LAS*1 316.00 195.87 120 120Nonylphenol 50.00 41.00 80 120Toluene 15.00 13.69 40 120Aroclor 1016 0.18 0.10 80 1202,4-dichlorophenol 4.70 2.08 120 80Ethylbenzene 3.50 3.20 40 80Phenol1 3.30 2.53 80 40Glucose1 3550.00 1420.00 14 40Anthracene 1.00 0.94 240 40Trichloroethylene 1.00 0.18 40 25Pentachlorophenol (PCP) 200.00 54.00 2 0

*LAS = linear alkylbenzenesulphonate1Dissolved in water before adding to soil. All other compounds were dissolved in 10 mlmethanol before addition to soil.

2Plus 2960 mg C as methanol kg-1 soil for all treatments except water control, methanolcontrol, LAS, phenol and glucose.

rhizobia were detected in soil with 175 mg kg-1) (Figure 1). The rhizobial populationdecreased by >99% at a PCP concentration of 75 mg kg-1 soil. The concentrationrange over which PCP caused a reduction in numbers from >100,000 cells g-1 soil to<100 cells g-1 soil was narrow, indicating the acute toxicity of this compound to R.leguminosarum bv. trifolii. Above this concentration range, no further reductions inpopulation size occurred, until at very high concentrations no rhizobia could bedetected (Figure 1).

The half-life of PCP in 10 different soils at 30 °C has been reported to be from 20-120days under aerobic conditions and 10-70 days under anaerobic conditions. Bacteriawhich degrade this compound, may be particularly sensitive to it and there are reportsof strong irreversible inhibition of soil microbial respiration by 200 mg PCP kg-1 soil(Zelles et al., 1989). It has been found that 200 mg PCP kg-1 soil to have prolongedeffects on soil ATP-content, substrate-induced respiration and substrate-induced heatoutput (Scheunert et al., 1995). These effects persisted even after a substantial declinein the PCP content of the soil. Schönborn and Dumpert (1990) found that a singleapplication of 50 kg PCP ha-1 in the field (equivalent to about 76 mg PCP kg-1 soil if itwas mixed into the top 5 cm) reduced the soil microbial biomass to such an extent that

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Figure 1: The effects of PCP additions to soil on the indigenious population of Rhizobiumleguminosarum biovar trifolium after 6 months.

it took 2 years for it to fully recover. They suggested that the metabolites of PCP werelikely to increase its toxicity to soil microorganisms. This persistence of the effects ofPCP and its breakdown products in the soil may explain the lack of recovery of therhizobial population in the experiments above. In this study, the effect of PCP onrhizobial numbers occurred at a much lower concentration (75 mg kg-1 soil) than thosereported by Zelles et al., (1989) or Scheunert et al., (1995).

All the organic compounds were added in the absence of sewage sludge and this maymean that the toxicity of the compounds is larger than it would be in the presence oflarge amounts of organic matter. However, under these conditions, only onecompound was toxic to the rhizobia. It could be concluded from this that toxicity dueto organic components is unlikely to explain the adverse effects of sewage sludge onsoil microbes.

Potentially toxic metals

The issues surrounding metals from sewage sludges can be summarised as:• Persistence and metal balances;• Extractability or bioavailability changes with time;• Crop uptake;• Microbial impacts.

The last issue is dealt with in the chapter by Witter, and will not be discussed here.

Persistence and metal balances

McGrath (1987) showed that the uptake of metals by crops grown over many years onthe Woburn Market Garden Experiment was responsible for the removal of very smallamounts of metals. If the removal in crops were the only route for loss of metalsdeposited in soil from applications of sewage sludge, the persistence time would bebetween 3,000 and 70,000 years (Table 11).

Transport of metals physically attached to soil particles during the cultivation of openplots was shown to be the largest loss from within the treated area of a sludged plot, tosurrounding soil. However, these losses remained within the topsoil, as shown by

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Table 11: Removal and residence times of metals from the soil of the Woburn Market GardenExperiment (after McGrath, 1987).

Metal Removal, 1960-1980 % of input from Residence(kg ha-1) sludges (years)

Zn 11.70 0.50 3700Cu 1.30 0.20 13100Ni 0.45 0.40 5700Cd 0.18 0.30 7500Pb 0.41 0.06 35000Cr 0.22 0.03 70000

detailed transects, soil profile analyses and modelling (McGrath and Lane, 1989).These investigations also showed that the leaching of metals on a sandy loam soilsome 25 years after the last sludge application was very small. More than 80% of eachof the metals measured could be accounted for in the topsoil (Zn, Cd, Cu, Ni, Cr, Pb),indicating a physical horizontal transport process. Others have found metal losseswhich have been attributed to leaching in other soil types, often with permanentvegetation, possibly containing more long-lived vertical channels (McBride et al.1997, Richards et al., 1998). In these channels, colloid-assisted transport of metalsand possibly POPs could occur.

Extractability or bioavailability changes with time

Two opposing hypotheses have been put forward to explain metal behaviour insludge-treated soils in the long term. The first is called the ‘time bomb’ hypothesis(Berrow and Burridge, 1980, McBride, 1995), in which metal availability is predictedto increase due to the decomposition of sludge organic matter. This, however, ignoresevidence from non-sludge contaminated soils which shows that other soil propertiesand chemical factors control metal solubility, when organic matter has not beenadded. The alternate hypothesis is that of ‘fixation’, which states that metals willgradually ‘revert’ (Lewin and Beckett, 1980) to more stable and insoluble forms in thesoil with time, particularly as the added organic matter decomposes.

Archived samples from the Woburn Market Garden Experiment were used to testthese hypotheses over a period of 20 years when sludge was applied, followed byalmost 25 years with no sludge application (McGrath et al., 2000). Two indicators ofchange were assessed: 1) changes in chemical extractability of metals in the soil, and2) changes in uptake by crops, which are shown in the next section.

Due to regular small applications of lime, the soil pH (water) in all the treatments atWoburn were similar and lay in the range 6-7. This is unique amongst long-termsludge experiments, where the pH usually drifts down because of the decompositionof the added organic matter. In practical situations, the possibility of a future changein pH has to be considered, especially if land is removed from arable agriculture andliming is stopped. The organic C concentration in soils that had received the highestrate of sludge was almost 3% in 1960 and decreased to 1.9% in 1984. All of theorganic treatments showed similar declines, but the control treatment increasedslightly from 0.9% before the experiment started to 1.0% in 1960, but has remainedlargely stable since then (McGrath et al., 2000).

Extractability of Zn and Cd was assessed with 0.1 M CaCl2 (Sauerbeck and Styperek,1985) and expressed as a percentage of the aqua regia total concentrations.Extractability ranged between 0.5 and 3.2% for Zn, and from 4 to 18% for Cd (Figure2). Sludge-amended soils consistently had higher percentages of CaCl2 extractable Znand Cd than the soils receiving inorganic fertilizer or farmyard manure. This isconsistent with several previous studies (Sanders et al., 1987; Sloan et al., 1997), andindicates that higher proportions of sludge-borne Zn and Cd than soil native Zn andCd were in soluble or exchangeable forms, and hence potentially higher

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bioavailability. Percentages of CaCl2 extractable Zn and Cd fluctuated over time, butthere was no clear evidence of either an increasing or a decreasing trend. However, forZn, there was an indication of lower extractability during the period after 1970 whenthe experiment was laid to grass, but there is no obvious explanation for this (Figure 2).

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Figure 2: Changes in extractability of soil Zn (top) and Cd (bottom) as a percentage of theaqua regia total metal concentration (after McGrath et al., 2000).

Crop uptake

Uptake of metals on sludge experiments has been studied for some time on both theWoburn (McGrath, 1987) and Braunschweig experiments (Lüben and Sauerbeck,1991a,b). In general, the findings are, in terms of relative transfer efficiency of metalsfrom soil to plants: Cd, Zn > Cu, Ni > Pb, Cr. For crops, it is usually observed thatmonocotyledons, including cereals, take up less than most broad-leaved crops (Lübenand Sauerbeck, 1991c).

Few crops were grown repeatedly on the Woburn Market Garden Experiment. Carrots(Daucus carota L.) and red beet (Beta vulgaris L.) were the only ones with samples ofthe same varieties grown in several different years still existing in the archive. Theslopes of the relationship between the concentration in the plant parts, against the totalconcentration in soil are a measure of the relative uptake in different years. Theserelationships were linear, and there was no evidence of a plateau within the ranges ofsoil Zn and Cd concentrations established in this experiment. Tables 12 shows theconcentration ranges in plants and the parameters of linear regressions for Zn and Cd.In the majority of cases, the percentage of variation accounted for by the linearregression (adjusted R2) was greater than 70% for both Zn and Cd. Several generalpoints can be observed: 1) the slopes for Zn and Cd fell broadly into similar ranges,indicating a similarity between the two metals; 2) vegetative tissues had greater slopesthan storage tissues (beet roots), indicating a physiological barrier in the transfer of Znand Cd from primary roots or vegetative tissues to storage organs; 3) crop speciesdiffered markedly in the slopes. For Zn, the slopes for red beet roots and tops wereapproximately 4 and 9 times, respectively, of those for carrot. For Cd, the slopes forred beet tops were 3-4 times of those for carrot tops, whereas the slopes for red beetroots were only 65-90% of those for carrot roots. The order of Cd accumulation indifferent plants was consistent with that reported elsewhere (Chaney et al., 1987;Grant et al., 1998).

Slopes for both Zn and Cd in carrot and red beet in 1985 were much higher than thosein the two previous years (Table 12). Although the differences between the two earlieryears were relatively small, there were increases in the slopes from 1963 to 1984 incarrot, and from 1983 to 1984 in red beet. Reasons for the seasonal differences are notclear. It is difficult to attribute the increasing trend of metal bioavailability, observedin this experiment, as evidence of the ‘time-bomb’ theory for two reasons. First,because the number of times the same crop was grown was not enough, and second,over the same period the ratio of metal to organic C did not change much (McGrath etal., 2000). However, the results do indicate that the bioavailability of sludge-bornemetals does not necessarily decrease in long-term, as suggested by Corey et al. (1987).

Recently, Chaudri et al. (2000) reported that the yield of peas grown on the fieldexperiment at Gleadthorpe decreased in relation to the Zn concentration in the soils,particularly above 200-300 mg Zn kg-1. This was concluded to be due to acombination of phytotoxicity and toxicity to the bacterial symbiont, Rhizobiumleguminosarum biovar viciae. Similar effects were seen on the population ofRhizobium leguminosarum biovar leguminosarum, the clover symbiont, which wasalso affected in the Woburn and Braunschweig sewage sludge experiments, at about

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the same total concentrations of Zn (McGrath et al., 1988, 1995, Giller et al., 1989,Chaudri et al., 1993).

However, most concern relating to food chain transfer of metals centres on Cd. In adraft EU Regulation on Contaminants in Food, Cd in cereal grains is limited to 0.1 mgkg-1 on a fresh weight basis (EU, 2000). Evidence from long-term sludge experimentson uptake by cereals is very scarce. Winter wheat grown in the Rosemaund frameexperiment exceeded the proposed limit in soil containing a total of 1 mg Cd kg-1,whilst in 1996 the limiting soil concentration was 1.5 mg Cd kg-1 (Chaudri, personalcommunication). The reason for the change in slope between grain and soil Cd is notknown, but could be associated with climatic differences and different varietiesgrown. Barley, on the other hand, appears to take up less Cd into grain than wheat(Adams et al., 2000), and the limiting soil concentration at the Woburn MarketGarden Experiment in a single year was 6 mg Cd kg-1.

Conclusions

For persistent organic pollutants:• Accumulation occurs in soils, but the persistence varies between different groups

and specific compounds within each group, increasing generally in the order:PCBs>CBs>PAHs>PCDD/Fs;

• The pathway soil-plant uptake seems relatively unimportant;• Ingestion of contaminated soils by grazing animals may be a more significant

pathway in the food chain.

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Table 12: Range of plant Zn and Cd concentrations (mg kg-1) and linear regression parametersbetween plant and soil metal concentrations (after McGrath et al., 2000).

Year Plant Tissue Range Zn Slope R2adj Range Cd Slope R2

adj

1963 Carrot Top 28-71 0.07 0.80 0.4-3.1 0.09 0.50Root 22-49 0.04 0.77 0.2-1.7 0.06 0.60

1984 Carrot Top 21-60 0.09 0.68 0.2-2.1 0.18 0.78Root 20-41 0.05 0.62 0.3-1.3 0.10 0.75

1985 Carrot Top 26-83 0.17 0.84 0.5-4.3 0.35 0.88Root 21-50 0.09 0.82 0.3-3.2 0.23 0.79

1983 Red beet Top 25-172 0.36 0.78 0.5-6.4 0.56 0.84Root 30-75 0.13 0.80 0.1-1.3 0.09 0.88

1984 Red beet Top 56-337 0.78 0.78 0.6-7.5 0.74 0.91Root 29-95 0.19 0.75 0.1-1.0 0.09 0.92

1985 Red beet Top 73-547 1.54 0.91 0.8-11.3 1.07 0.94Root 34-146 0.34 0.89 0.1-1.6 0.15 0.93

• Organic pollutants such as nonylphenol do not show significant movement towardsgroundwater, as least in a sandy loam soil;

• Most classes of POPs have no detectable effects on soil microbial populations, withthe exception of PCP added to soil without sewage sludge.

For metals:• Metals from sludge accumulate in soils, and their solubility remains higher than

native metals for a long period of time;• Uptake by crops remains high for extended periods in sludge-treated soils;• Cadmium concentrations in grain may exceed the EU Regulation for wheat grain,

on sludged soils containing as little as 1 mg kg-1 Cd;• Metal availability certainly does not decrease with time after sludge applications

cease, and increased uptake in some years may be due to climatic or other factors.

References

Adams, M.L., McGrath, S.P., Zhao, F.J., Nicholson, F.A. and Sinclair, A.H. (2000) Lead andcadmium as contaminants in UK wheat and barley. Proceedings of HGCA Conference: CropManagement into the Millennium, Homerton College, Cambridge, HGCA, London. pp. 10.1-10.10.

Alcock, R.E., Johnston, A.E., McGrath, S.P., Berrow, M.L. and Jones, K.C. (1993) Long-termchanges in the polychlorinated biphenyl content of United Kingdom soils. Environmental Scienceand Technology 27, 1918-1923.

Alcock, R.E., McGrath, S.P. and Jones, K.C. (1995) The influence of multiple sewage sludgeamendments on the PCB content of an agricultural soil over time. Environmental Toxicology andChemistry 14, 553-560.

Berrow, M.L. and Burridge J.C. (1980) Trace element levels in soils: effects of sewage sludge.Inorganic Pollution and Agriculture. London, MAFF Reference Book No. 326. HMSO, pp. 159-183.

Chaudri, A.M., McGrath, S.P., Giller, K.E., Rietz, E. and Sauerbeck, D.R. (1993) Enumeration ofindigenous Rhizobium leguminosarum biovar trifolii in soils previously treated with metal-contaminated sewage sludge. Soil Biology and Biochemistry 25, 301-309.

Chaudri, A.M., McGrath, S.P., Knight, B.P., Johnson, D.L. and Jones, K.C. (1996) Toxicity oforganic compounds to the indigenous population of Rhizobium leguminosarum biovar trifolii in soil.Soil Biology and Biochemistry 28, 1483-1487.

Chaudri A.M., Allain, C.M.G., Barbosa-Jefferson, V.L., Nicholson, F.A., Chambers,B.J. andMcGrath, S.P. (2000) A study of the impacts of Zn and Cu on two rhizobial species in soils of a longterm field experiment. Plant and Soil, in press.

Chaney, R.L., R.J.F. Bruins, D.E. Baker, R.F. Korcak, J.E. Smith, and Cole D. (1987) Transfer ofsludge-applied trace elements to the food chain. In A.L. Page, T.J. Logan, and J.A. Ryan (eds.) Landapplication of sludge. Lewis Publ., Chelsea, MI. pp. 67-99.

Corey, R.B., L.D. King, C. Lue-Hing, D.S. Fanning, J.J. Street, and Walker J.M. (1987) Effects ofsludge properties on accumulation of trace elements by crops. In A.L. Page, T.J. Logan, and J.A.Ryan (eds.) Land application of sludge. Lewis Publ., Chelsea, MI. pp. 25-51.

EU (2000) Setting maximum levels for certain contaminants in foodstuffs. Amending Commissionregulation (EC) No 194/97 of 31 January 1997. Draft Commission Regulation on Contaminants inFoodstuffs. January 2000.

German Federal Ministry of the Environment (1992) Sewage sludge ordinance. Federal Law Gazette,15 April.

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Giller, K.E., McGrath, S.P. and Hirsch, P.R. (1989) Absence of nitrogen fixation in clover grown onsoil subject to long term contamination with heavy metals is due to survival of only ineffectiveRhizobium. Soil Biology and Biochemistry 21, 841-848.

Grant, C.A., W.T. Buckley, L.D. Bailey, and Selles F. (1998) Cadmium accumulation in crops.Canadian Journal of Plant Science 78, 1-17.

Jones, K.C., Johnston, A.E. and McGrath, S.P. (1994) Historical monitoring of organic contaminantsin soils. In: Long-term experiments in agricultural and ecological sciences. Eds. R.A. Leigh and A.E.Johnston. Chapter 9, CAB International, pp. 147-163.

Jones, K.C., Johnston, A.E. and McGrath, S.P. (1995) The importance of long- and short-term air-soilexchanges of organic contaminants. International Journal of Environmental and Analytical Chemistry59, 167-178.

Lamy, I., Bourgeois, S., and Bermond, A. (1993) Soil cadmium mobility as a consequence ofsewage-sludge disposal. Journal of Environmental Quality 22, 731-737.

Lewin, V.H. and Beckett P.H.T. (1980) Monitoring heavy metal accumulation in agricultural soilstreated with sewage sludge. Effluent and Water Treatment Journal 20, 217-221.

Lüben, S. and Sauerbeck, D. (1991a) Vergleich der Resultate von Gefä- und Feldversuchen. In:Auswirkungen von Siedlungsabfällen auf Böden, Bodenorganismen und Pflanzen. Eds. Sauerbeck,D. and Lüben, S. Berichte aud der Ökologischen Forschung, Band 6, Forschungszentrum Jülich,GmbH, pp. 289-313.

Lüben, S. and Sauerbeck, D. (1991b) Prüfung der Versuchsergebnisse auf standortspezifischeUnterschiede. In: Auswirkungen von Siedlungsabfällen auf Böden, Bodenorganismen und Pflanzen.Eds. Sauerbeck, D. and Lüben, S. Berichte aud der Ökologischen Forschung, Band 6,Forschungszentrum Jülich, GmbH, pp. 314-326.

Lüben, S. and Sauerbeck, D. (1991c) Transferfaktoren und Tranferkeoffizienten für denSchwermetallübergang Boden-Pflanze. In: Auswirkungen von Siedlungsabfällen auf Böden,Bodenorganismen und Pflanzen. Eds. Sauerbeck, D. and Lüben, S. Berichte aud der ÖkologischenForschung, Band 6, Forschungszentrum Jülich, GmbH, pp. 180-223.

Marcomini, A., Capel, P.H., Lichtensteiger, T. Brunner, P.H. and Giger W. (1989) Behaviour ofaromatic surfactants and PCBs in sludge treated soil and landfills. Journal of Environmental Quality18, 523-528.

McBride, M.B. (1995) Toxic metal accumulation from agricultural use of sludge: are USEPAregulations protective? Journal of Environmental Quality 24, 5-18.

McBride, M.B., Richards, B.K., Steenhuis, T., Russo, J.J. and Sauve, S. (1997) Mobility andsolubility of toxic metals and nutrients in soil fifteen years after sludge application. Soil Science 162,487-500.

McGrath, S.P. (1987) Long-term studies of metal transfers following applications of sewage sludge.In: Pollutant Transport and Fate in Ecosystems. Eds. P.J. Coughtrey, M.H. Martin and M.H.Unsworth. Special Publication No.6 of the British Ecological Society, Blackwell Scientific, Oxford,pp.301-317.

McGrath, S.P. and Lane, P.W. (1989) An explanation for the apparent losses of metals in a long-termfield experiment with sewage sludge. Environmental Pollution 60, 235-256.

McGrath, S.P., Giller K.E., and Brookes P.C. (1988) Effects of potentially toxic metals in soil derivedfrom past applications of sewage sludge on nitrogen fixation by Trifolium repens L. Soil Biology andBiochemistry 20, 415-424.

McGrath, S.P., Chaudri, A.M. and Giller, K.E. (1995) Long-term effects of metals in sewage sludgeon soils, microorganisms and plants. Journal of Industrial Microbiology 14, 94-104.

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McGrath S.P., Zhao F.J., Dunham S.J., Crosland A.R., and Coleman K. (2000) Long-term changes inthe extractability and bioavailability of zinc and cadmium after sludge application. Journal ofEnvironmental Quality, in press.

McLachlan, M.S. (1992) Exposure toxicity equivalents (ETEs): A plea for more environmental chemistryin dioxin risk assessment. Proceedings, Dioxin 1992 Organohalogen Compounds, 10, 327-330.

Moza, P., Weisgerber, I. and Klein, W. (1979) Studies with 2,4’,5-trichlorobiphenyl-14C and2,2’,4,4’,6-pentachlorobiphenyl-14C in carrots, sugar beets and soil. Journal of Agricultural FoodChemistry 27, 1120-1124.

Oehme, M. (1991) Dispersion and transport paths of toxic persistent organochlorines to the Arctic-levels and consequences. Science of the Total Environment 106, 43-53.

Richards, B.K., Steenhuis, T.S., Peverly, J.H. and McBride, M.B. (1998) Metal mobility at an old,heavily loaded sludge application site. Environmental Pollution 99, 365-377.

Sauerbeck, D.R., and Styperek P. (1985) Evaluation of chemical methods for assessing the Cd and Znavailability from different soils and sources. In R. Leschber, R.D. Davis and P. L’Hermite (eds.).Chemical Methods for Assessing Bio-available Metals in Sludges and Soils, Elsevier AppliedScience, London, UK. pp. 49-66.

Sanders, J.R., S.P. McGrath, and Adams T. McM. (1987) Zinc, copper and nickel concentrations insoil extracts and crops grown on four soils treated with metal-loaded sewage sludges. EnvironmentalPollution 44, 193-210.

Scheunert, L. Attar, A. and Zelles, L. (1995) Ecotoxicological effects of soil-boundpentachlorophenol residues on the microflora of soils. Chemosphere 30, 1995-2009.

Schönborn, W. and Dumpert K. (1990) Effects of pentachlorophenol and 2,4,5-trichlorophenoxyacetic acid on the microflora of the soil in a beech wood. Biology and Fertility ofSoils 9, 292-300.

Sewart, A., Harrad, S.J., McLachlan, M.S., McGrath, S.P. and Jones, K.C. (1995) PCDD/Fs and non-o-PCBs in digested UK sewage sludges. Chemosphere 30, 51-67.

Sloan, J.J., Dowdy R.H., Dolan M.S., and Linden D.R. (1997) Long-term effects of biosolids applicationson heavy metal bioavailability in agricultural soils. Journal of Environmental Quality 26, 966-974.

Wang, M.-J., McGrath, S.P. and Jones, K.C. (1992) The chlorobenzene content of archived sewagesludges. The Science of the Total Environment 121, 159-175.

Wang, M.-J., and Jones, K.C. (1994) Behaviour and fate of chlorobenzenes (cbs) introduced into soil-plant systems by sewage-sludge application - a review. Chemosphere 28,1325-1360

Wang, M-J., McGrath, S.P. and Jones, K.C. (1995) Chlorobenzenes in field soil with a history ofmultiple sewage sludge applications. Environmental Science and Technology 29, 356-362.

Wild, S.R., McGrath, S.P. and Jones, K.C. (1990a) The polynuclear aromatic hydrocarbon (PAH)content of archived sewage sludges. Chemosphere 20, 703-716.

Wild, S.R., Waterhouse, K.S., McGrath, S.P. and Jones, K.C. (1990b) Organic contaminants in anagricultural soil with a known history of sewage sludge amendments: polynuclear aromatichydrocarbons. Environmental Science and Technology 24, 1706-1711.

Wild, S.R., Berrow, M.L., McGrath, S.P. and Jones, K.C. (1992) Polynuclear aromatic hydrocarbonsin crops from long-term field experiments amended with sewage sludge. Environmental Pollution76, 25-32.

Wild, S.R., Harrad, S.J. and Jones K.C. (1994) The influence of sewage sludge applications toagricultural land on human exposure to polychlorinated dibenzo-p-dioxins (PCDDs) and –furans(PCDFs). Environmental Pollution 83, 357-369.

Zelles, L. El-Kabbany, S., Scheunert, I. and Korte F. (1989) Effects of pentachlorophenol-14C andHgCl2 on the microflora of various soils in comparison to biodegradation and volatilization.Chemosphere 19, 1721-1727.

Hygienic aspects of sludge reuse

Prof. Dr. Reinhard BöhmUniversität Hohenheim, Institut für Umwelt und Tierhygiene sowieTiermedizin mit Tierklinik – D-70593 Stuttgart

Introduction

As other urban wastes, sewage sludge may contain pathogens of different kinds beinginfectious for different species of animals and plants as well as for humans. The originand nature of organic wastes like the different types of sludge is always causing ahygienic risk in storage, collection, handling, processing and utilisation. Those risksare existing either if the organic wastes are collected and processed source separated(biowastes) or if they are collected together with other wastes from households orrelevant processing industries, if they are generated in treatment of industrial ormunicipal wastewater, or if the sludge results from industrial processing of organicmaterial. Therefore hygienic principles must be followed in collection, transport,processing, storage and distribution of such materials. The following types and originsof sludge which should be regarded here are sewage sludge, sludge from anaerobictreatment of biowastes and sludge from co-digestion plants (sewage sludge +biowastes). Recycling of organic material to agriculture is a desirable aim from thepoint of view of saving raw materials which are of limited availability as phosphorusbut this aim may conflict with the necessity to protect man, animals and plants fromundesired infections as well as with general aims of environmental protection. In thisconnection only the hygienic aspects are covered, other contributions will focus on therisks due to undesired organic and inorganic pollutants.

Hygienic risks

Three main types of risks mainly related to pathogens for man and animals have to beconsidered in collection and processing or solid organic wastes an sludge (Böhm,1995; Böhm et al., 1996; Strauch, 1998);• occupational health risks;• risks concerning the product safety;• environmental risks.

Occupational health considerations in collecting and processing organic wastes andsludges are not the main subject of this contribution, more details may be taken fromHicky and Reist (1975), Grüner (1996) and Böhm (1998). Hygienic risks due the

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sludge and related products will be regarded mainly here. This includes the di-recttransmission of pathogens to man or animals and plants of agricultural impor-tance aswell as introducing them into the biozoenosis and environment by the appli-cationsuch material as organic fertilizers.

Pathogens in sewage sludge

The basic risk factor is the occurrence of pathogens in sewage sludge which gives thestarting point for epidemiological reflections and necessary precautions. The Tables 1-4 are giving a survey on such pathogens according to Strauch (1991).

From the variety of bacterial pathogens Salmonella spp. are the most relevant sincethey can infect or contaminate nearly all living vectors from insects to mammals.

Multiresistant bacteria are coming more and more into focus since their transmissionvia environment as well as the introduction of resistance genes into other bacteria maycause tremendous problems in human and veterinary medicine. Regarding the viralpathogens, enteroviruses and rotavirus are the most relevant ones from the point ofview of environmental risks (Metzler et al. 1996). Special regard must be paid to theparasitic pathogens, not only to eggs of round- and tapeworms but to Giardia lambliaand especially Cryptosporidia parvum too.

Pathogens in sludges of other origin

It depends on the origin of sludges which spectrum of pathogens could be found in whichconcentrations. Sludge of animal origin as from slaughterhouses or meat processing

Table 1: selection of bacterial pathogens to be expected in sewage and sewage sludge, strauch(1991), modified.

Primary pathogenic Secondary pathogenicSalmonella spp. EscherichiaShigella spp. KlebsiellaEscherichia coli EnterobacterPseudomonas aeruginosa SerratiaYersinia enterocolitica CitrobacterClostridium perfringens ProteusClostridium botulinum ProvidenciaBacillus anthracis Multiresistant bacteriaListeria monocytogenesVibrio choleraeMycobacterium spp.Leptospira spp.Campylobacter spp.StaphylococcusStreptococcus

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Table 2: Selection of viruses excreted by humans which can be expected in sewage andsewage sludge (Strauch, 1991; Hurst, 1989).

Virus group Number Diseases or symptoms causedof types

EnterovirusPoliovirus 3 Poliomyelitis, meningitis, feverCoxsackievirus A 24 Herpangina, respiratory disease,meningitis, feverCoxsackievirus B 6 Myocarditis, congenital heart anomalies, meningitis,

respiratory disease, pleurodynia, rash, feverEchovirus 34 Meningitis, respiratory disease, rash, diarrhoea, feverNew “numbered” 4 Meningitis, encephalitis, respiratory disease, acuteenteroviruses haemorrhagic conjunctivitis, feverAdenovirus 41 Respiratory disease,eye infectionsReovirus 3 Not clearly establishedHepatitis A-virus 1 Infectious hepatitisRotavirus 4 Vomiting and diarrhoeaAstrovirus 5 GastroenteritisCalicivirus 2 Vomiting and diarrhoeaCoronavirus 1 Common coldNorwalk agent 1 Vomiting and diarrhoeaSmall round viruses 2 Vomiting and diarrhoeaAdenoassociated virus 4 Not clearly established but associated with respiratory

disease in childrenParvovirus 2 One type possibly associated with enteric infection

Table 3: Selection of pathogenic yeasts and fungi to be expected in sewage and sewage sludge(Strauch 1991).

Yeasts FungiCandida albicans Aspergillus spp.Candida krusei Aspergillus fumigatusCandida tropicalis Phialophora richardsiiCandida guillermondii Geotrichum candidumCrytococcus neoformans Trichophyton spp.Trichosporon Epidermophyton spp.

Table 4: Selection of parasites to be expected in sewage and sewage sludge, Strauch (1991),modified.

Protozoa Cestodes NematodesCryptosporidia parvum Taenia saginata Ascaris lumbricoidesEntamoeba histolytica Taenia solium Ancylostoma duodenaleGiardia lamblia Diphyllobothrium latum Toxocara canisToxoplasma gondii Echinococcus granulosus Toxocara catiSarcocystis spp. Trichuris trichiura

industries will contain generally mostly animal pathogens or zoonotic agents. Table 5gives an impression what bacterial counts could be found in bovine rumen content withrespect to selected species, and Table 6 summarizes the prevalance and resistance ofparasitic agent from the gut of cattle and their potential hygienic hazard. Nearly all gutrelated pathogens could be found in slaughterhouse effluents. If sludges are of plant originor had been processed by using plant material, they may contain plant-pathogenic viruses,fungi, bacteria, parasites and undesired weeds. This will cause an additional phytohygienicrisk if the final product should be used in agriculture as fertilizer (Böhm et al., 1999).

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Table 5: Bacterial count* including Salmonella of rumen content collected for further processing.

Sample TBC EBA E. coli FCS Salmonella pH dm02.03.95 5.7x107 4.3x105 4.3x105 2.1x106 7.5x102 6.02 19.9011.10.95 4.9x108 1.5x106 2.3x104 2.5x105 4.3x100 7.48 12.92

S. Thyphimur.08.01.96 (1) 4.8x108 2.3x107 2.3x107 7.5x106 7.5x102 6.68 19.92

(2) 5.4x108 2.3x107 9.3x106 2.3x107 4.3x103 7.41 19.92(3) 5.7x108 2.3x107 9.3x106 3.8x107 2.3x106 7.07 19.92(4) 6.9x108 2.3x107 2.3x107 2.3x107 4.3x103 7.20 19.92(5) 9.9x108 4.3x107 9.3x106 4.3x107 2.3x103 7.85 19.92

07.03.96 (1) 4.4x108 2.9x105 9.3x104 9.3x105 9.3x102 7.25 21.08(2) 4.6x108 2.4x106 9.3x105 2.4x106 4.3x103 7.15 21.08(3) 8.4x107 2.4x106 2.4x106 9.3x105 2.4x103 6.79 21.08(4) 3.6x108 9.3x107 4.3x105 9.3x105 2.4x103 7.24 21.08(5) 3.1x108 9.3x105 9.3x105 2.4x106 4.3x103 7.16 21.08

* CFU/gTBC = Total Bacterial Count 37 °C FCS = Fecal StreptococciEBA = Enterobacteriaceae dm = dry mater

Table 6: Prevalence and resistance of parasitic agents from the gut of cattle and their potentialhygienic hazard (Bürger and Stoye, 1978, modified).

Parasite Prevalence1 Resistance2 Priority as a hygienic hazardProtozoa

Cryptosporidia +++ +++ 1Eimeria spp. +++ +++ 2

HelminthsTrichostrongylid spp. +++ ++ 3Strongyloides papillosus ++ +Oesophagostomum spp. ++ ++Fasciola hepatica ++ +++ 4Dictyocaulus viviparus + +Trichuris spp. + ++Dicrocoelium dendriticum + +++Moniezia spp. + +Toxocara vitulorum + +++

1+++ regular ++ frequent + occasional 2+++ high ++ intermediate + low

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Epidemiological importance of sludge related pathogens

Pathogens may survive for a remarkable period of time in sludges and theenvironment. This is a base of the resulting epidemiological risks (Strauch 1998). Thepossible ways of transmission are summarized in Table 7.

The direct or indirect transmission of zoonotic agents to farm animals is generallyregarded as the most relevant fact in connection of agricultural utilization of untreatedor unsuffient treated sludge. This direct relationship between fertilizing with sewagesludge and resulting infection in cattle fed with forage after spreading had beenreported by Breer (1981) for Salmonella (Fig. 1). Much more earlier the transmissionof parasites eggs had been observed.

Direct transmissions to humans via products based on sludge or containinginsufficient treated sludge in households (Ottolenghi et Hamparian, 1987) although arelatively rare event-must be regarded as real risk. In addition accidental contact ofimunocompromised persons to contaminated sludge or sludge products may result inan infection. The occupation risks in processing and handling of sludge and relatedproducts must be taken into account but will not be regarded here in details. Theindirect transmission to humans is of special importance, because the introduction ofpathogens into the food chain via contaminated fertilizer leading to contaminatedanimal feed and this to infection of farm animals and / or excretion of pathogens is ofbasic epidemiological significance. The risk of transmission of pathogens to humanfood by living vectors as insects, rodents and birds form processing handling andagricultural utilization of slurry has to be taken into account too.

Table 7: Epidemiological importance of processed wastes and residuals as well as of theresulting products.

A. Direct transmission to farm animals- Contamination of meadows- Introduction of pathogens by storage and processing close to susceptible animals- Aerogenic transmission by spreading the materials into farm land

B. Direct transmission to humans- Handling of contaminated products in the household- Occopational exposure to contaminated products- Accidental transmission to immuncompromised persons

C. Indirect transmission to farm animals- Via feed from contaminated sites- Via living vectors

D. Indirect transmission to humans- Via introduction of zoonotic agents into the foodchain- Via food contaminated by living vectors

E. Introduction into the environment- Generation of carriers in the fauna- Introduction into the microflora

Table 8 gives an example how birds can become carriers of Salmonella. One of thesources of infection in sea-gulls has been founded to bee a sewage treatment plants.The further ways of introduction of a certain lysortype of Salmonella Enteritidis couldbe demonstrated by Köhler (1993). He identified the waste delivered from West-Berlin to a waste disposal site in the former GDR and followed the introduction of thispathogen via birds into the chicken populations and finally to humans via productscontaining eggs. This historical example can be followed in Table 9. Williams et al.(1977) as well as several other authors like Coulsen et al. (1983), Mayr (1988)described the importance of vectors in the transmission of Salmonella to farm animalsand humans. Foster and Spector (1995) described specific molecular mechanismsresponsible for the ability of Salmonella to survive the environmental stress.

This means that introduction of pathogens in the environment leads to carriers in thenatural fauna and moreover to an introduction of transmissible undesired properties ofbacteria like antibiotic resistance plasmids into the microflora and biozoenoses. TheFigure 2 shows a simplified scheme of the ways drugs can be introduced intoenvironment, with respect to antibiotics this means that selection of resistantpathogens could take place at every stage of distribution and thus elevates thepossibility of speeding resistant bacteria in an uncontrolled manner.

Inactivation of pathogens by adequate treatment of sludge

Biological, chemical and physical methods may be applied in order to inactivatepathogens. All methods may be successful in order to reach this purpose but somehave special limitations. Nature and number of pathogens basically determines the

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Figure 1: Seasonal distribution of Salmonella isolations from dairy cattle fed with forage afterspreading of sewage sludge during the winter and after hay making (Breer, 1981).

Table 8: Detection of Salmonella in sea-gull droppings (Hellmann, 1977).

References Site Number of SalmonellaNumber of PredominantSamples positive Serovars Serovars

Pagon et al. (1974) Lake konstanz 996 6,9 8 S. BrandenburgS. TyphimuriumS. ManchesterS. Newport

Heilmann et al. (1973) Steinhuder meer 95 9,5 6 S. Typhimuriumpurification pond 187 13,9 12 S. Agonaof sugar plant S. Montevideolehrte

Wuthe, H.H (1973) Breeding colony 196 12,25 12 S. TyphimuriumS. ThompsonS. InfantisS. Enteritidis

Edel, W. et al. (1972) Walcheren (NL) 60 26,7 10 S. TyphimuriumS. MontevideoS. Infantis

Müller, G. (1965) Hamburg, waste 1037 35,6 13 S. Typhimuriumwater purification 134 76,9 S. Paratypi Bplant S. Manchester

S. Infantis

Table 9: Time table of transmission from Salmonella Entertidis (lysotype 17) from WestBerlin wastes to birds of the Schöneiche waste disposal site in former GDR (Köhler, 1993).

ORIGIN 1989 1990 1991 1992 TotalI II III IV I II III IV I II III IV I II III IV

ChildrenBerlin-West 5 10 8 23Waste Disposal Site Sea Gulls 3 2 5and CrowsDove Oranienburg 1 1 2Chicken 17 12 12 2 43Chicken Transport 5 3 8CagesHumans ZossenPotsdamBrandenburg 1 4 3 8 2 2 20Cake Pudding 1 1 2Black Grouse 1 1Total 5 10 11 23 15 12 2 2 4 6 8 2 3 104

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requirements concerning the applied process, as well as the epidemiology, e.g. theoccurrence and distribution of the relevant pathogens in the target region. It seemstherefore not reasonable to define the requirements to the process for example assporocidal, because anthrax caused by sporeforming bacteria is an extremely rareinfection in northern, central and western Europe. In addition, due to other legalrequirements, the possibility that it will be introduced into the wastewater and sludge

Figure 2: Simplified diagram showing the relationship between medical product uses andenvironmental risk assessment schemes.

is nearly zero. But Salmonella may be found regularly in wastewater and in sludge andthe number of enteric infection caused by this pathogen is steadily rising, it may affecta broad spectrum of hosts and faecal media like sewage sludge have shown to beimportant in the epidemiology of salmonellosis. Thus a sludge treatment method mustinactivate those types of pathogens with sufficient safety, e.g. at least for 5 log steps.

Biological treatment

The following ways are reported to be in principal effective in producing a hygienicsafe sludge:• Aerobic thermophilic stabilization• Anaerobic thermophilic treatment• Composting of solid phase• Composting with bioorganic solids• Long-term storage

The aerobic thermophilic process should be operated at least as two-stage reactors(two vessels in series connection) to avoid the microbiological disadvantages ofhydraulic short-circuits. As for retention times, in the complete system at least fivedays have to be calculated, if the reactors are of equal volume.

Under consideration of the batch-type operation (e.g. one hour feeding per day) and23 hours stabilisation (exposure time) and of the temporary decrease of temperatureinevitably connected with this type of operation, the following reaction times andtemperatures are necessary:• 23 hours at 50 °C or• 10 hours at 55 °C or• hours at 60 °C.

This is easy to achieve in the second stage of treatment (second reactor) after using thefirst reactor to elevate the temperature to a level of 40 °C to 50 °C.

Anaerobic thermophilic treatment is another method leading to reliable disinfection. Atwo stage process is to prefer a one step treatment. The reactors must be run in abatch-type operation too. A temperature of at least 53 °C and a real exposure time ofat least 20 h must be kept for hygienisation.

Composting may be done in reactors or in windrows. Details for the operation ofseveral type of reactors had been described by Strauch (1998). The minimumrequirement is maintaining a temperature of at least 60 °C for one week in all parts ofthe material. The initial water content of the material should not exceed 70%. Thereactor passage shall be followed by a phase of curing the material in windrows orpiles of at least two weeks with at least one turning or in a second reactor by which thenecessary security of the sanitation process is ensured.

For composting in windrows a temperature of at least 55 °C for at least two weeksshould be kept. The windrow should be turned at least one time. Generally theprepared fresh compost from reactors or conventional windrows is piled further in

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windrows, which are turned twice a week. After a residence time of 8-12 weeks, thecompost will be matured. Then the material is transferred to the curing area.Depending upon the degree of mineralization required, a further storage period maybe necessary (Strauch, 1998).

Long term storage may be regarded as "biological" method too. There are a lot offactors influencing the starvation of bacteria and parasites as well as the inactivation ofviruses. If anaerobically or aerobically treated sludge should be safe from the point ofview of hygiene, the minimum storage time must be at least one year according to Pike(1983) and Haible (1989). If a lower hygienic standard is accepted in combination withrestrictions in application, half a year of storage time (batch wise) is enough for asignificant reduction of most bacterial pathogens but not for the relevant parasites eggs.

Chemical treatment

The following chemicals had been described to be applied for the disinfection ofsludge:• Lime (Ca(OH)2, CaO)• Peracetic Acid• Sodium Hydroxide• Formaldehyde

Due to several reasons lime either as slaked lime or as quicklime are the favourablechemicals if the sludge should be used in agriculture.

According to Strauch (1998), Ca(OH)2 (calcium hydroxide, lime hydroxide, slakedlime) is used for sanitation of liquid sludge before its use or for conditioning of thesludge before dewatering. In both cases the addition of lime results in an increase ofthe pH as a function of the amount of lime added and the properties of the sludge. Thewet addition of lime as lime milk should be given preference to lime powder, becauseof the better mixing and sanitising effect.

The limitations of using this type of lime are the low activity against parasite eggs andoocysts. This limitations can be compensated by storing the treated sludge for at least3 month. Generally the effect depends on the dry matter content of the sludge. Table10 shows this relationship.

Table 10: Recommendation for the treatment of sewage sludge with slaked lime (lime milk)according to the dry matter content (Strauch, 1998).

Dry matter % Kg Ca (OH)2/m3 (Lime Milk) Remarks1-3 6 Homogenous mixture of lime3-5 10 and sludge; pH 12.5 after6 12 liming; 24 hours reaction time7 14 at pH≥ 12 before delivery. For 8 16 destruction of ascaris eggs a9 18 reaction time of three months is10 20 necessary

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In particular cases the supervising authority must decide whether it is necessary tostore the sludge for three months after liming, in order to destroy ascaris eggs. Thiscan be dependent on their content in the relevant sludge and from the epidemiologicalrisk connected with the intended field of application.

Quicklime initiates besides high pH values also high temperatures by exothermicreactions. By that combination of high pH (>12) and high temperatures between 60 °Cand 70 °C also Ascaris eggs are destroyed within twenty-four hours, as well as reo-,polio-, parvo- and ECBO-viruses (Strauch, 1984).

The minimum requirements for the successful application of quicklime is a treatmentby which a pH-value of at least 12 and a temperature of at least 55 °C is kept for atleast 2 h and the treated lime must be stored for at least 24 h before further utilization.

Physical treatment

Mainly three different ways of treatment for destroying pathogens in sewage sludgeare described:• Pasteurization• Thermal drying• Irradiation

Pasteurization had been intensively studied and different techniques and combinationswith aerobic and anaerobic processes are described in literature (Philipp, 1981;Strauch, 1998).

During pasteurisation raw sewage sludge is heated to temperatures below 100 °C, butat least 65 °C, for at least thirty minutes. This is done prior to a stabilisation process asso-called pre-pasteurisation. A commination of larger particles prior to thepasteurisation process is necessary. To ensure that all sludge particles are exposed tothe reaction temperature and time, their size may not exceed 5 mm.

Other temperature/time combinations, for example

70 °C - 25 minutes75 °C - 20 minutes80 °C - 10 minutes

can also be used. Even at still higher temperatures, a reaction time lower than tenminutes is not effective. It must be emphasised that pasteurising the sludge first,followed by mesophilic anaerobic digestion, is utmost important. Initially sludge waspasteurised after mesophilic digestion (post-pasteurisation), but internationalexperiences showed a high degree of re-infection. Therefore, this technique wasregarded as a not reliable disinfection method and was finally abandoned (Strauch,1998).

In order to have a certain safety margin it should be recommended to use a thermaltreatment of liquid sludge at a temperature of at least 70 °C for at least 30 min,followed by mesophilic anaerobic digestion (at 35 °C).

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Figure 3: Influence of time and temperature on some selected pathogens isolated from sewagesludge and septic tanks (Feachem et al., 1983).

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Thermal drying is a good method for the inactivation of pathogens. The only problemwhich should be recognized in this connection is that dryness stabilizes mostmicroorganisms, thus the thermal inactivation must take place as long as enough wateris present in the material. A low final water content prevents further microbial activityin the product.

Therefore thermal drying with the reduction of the water content to less than 30%should be done in a way that during the initial drying phase at least 70 °C (or 80 °C)are kept for 1 h an aw-value (water activity) of the material above 0,9 during this time.

Irradiation is not acceptable for the public but is in principle effective in destroyingpathogens in sewage sludge (IAEA, 1975; Lessel, 1985).

For all processes connected with thermal inactivation the recommendation ofFeachem et al. (1983) given in Figure 3 should be taken into account.

Strategies to achieve hygienic safety in treatment and use of organic sludge

A compilation of bacterial, fungal, parasitic and viral pathogens for man and animalswhich may be present in organic wastes is given above. With regard to plantpathogens which may be of importance if other sludges as sewage sludge shall be usedwhich contain significant amounts of material of plant origin an extensive list ofviruses, bacteria, fungi and seeds is given by Menke (1992).

Since it is impossible to supervise the treated sludge for each of the pathogenic agentswhich may occur, other strategies have to be used in order to assure the hygienicsafety of the processed material. The first step in such a strategy is to find out arepresentative indicator organism which may be used for checking the product forhygienic safety as well as for evaluating the treatment process for its capability toinactivate pathogens which are of epidemiological relevance. The second step whichis necessary in this connection is to define hygienic requirements for the treatmentitself, since due to the high volume of the product to be controlled as well as to theinhomogenety of distribution of pathogens in the material only products processed ina validated process should be distributed to the consumer or user. This means that thefollowing strategies must be combined with each other in order to assure hygienic safeutilization of the processed sludges• Validation of treatment (disinfection by chemical, physical or biological means)• Continuous registration of the relevant process parameters (e.g. temperature, pH-

value, exposure time)• Microbiological supervision of the final product (indicators)• Restriction for the utilisation of the final product.

Validation of treatment

The validation of the treatment with respect to hygienic safety for animals, man and ifnecessary plants may be done in several ways.

The German LAGA M 10 (1995) offers a relatively broad approach in solving thisproblem with respect to composting based on the ATV (German Association ofWastewater Experts) recommendations from 1988 for sewage sludge treatment.Process safety concerning the inactivation of relevant transmissible agents for manand animals is validated in two steps. The first step is the validation of the process asdesigned by the producer of the technical equipment in a basic procedure, the secondstep is a putting into service validation of a treatment process at the plant with theinput material under practical conditions. In both validation procedures Salmonellasenftenberg W 775 (H2S negative) is used as a test organism exposed in speciallydesigned test carriers (Rapp, 1995; Böhm et al., 1997)

Several other test organisms are in discussion for the same purpose. The mostimportant are• Enterococci• Escherichia coli• Campylobacter• ECBO virus• Bovine Parvovirus (BPV)

Enterococci may be used, but if the carriers are exposed to a composting process itmay happen that the test material is contaminated with indigenous Enterococci. Thedifferentiation between indigenous flora and test strain is not possible under the givencircumstances, other the proposed Salmonella Senftenberg which is rarely present inthe material and can be easily identified by natural marker (H2S negative).Escherichia coli and Campylobacter jejuni are not as resistant as the above mentionedSalmonella strains, the same applies for ECBO-virus. The bovine parvo virus (BSV)ismuch more resistant than Salmonella and has still to be taken into account, butreisolation and propagation are very labour and cost intensive. Virology requiresspecialized laboratories this is for a general purpose a strong limitation but someindications are given for using BPV.

If phytohygienic safety is required the test organism to be used are Tobacco mosaicvirus, Plasmodiophora brassicae and seeds of Lycopersicon lycoperisicum (L) breedSt. Pierre (Bruns et al. 1994, Pollmann and Steiner, 1994). Testing is done twice, insummer- and in wintertime. This is a very complete and safe system, if due toeconomical consideration the system should be simplified and only a one stepprocedure should be the aim, it must be the putting into service validation. A schemehow this validation could be organized taking into account the annual throughput ofmaterial in the plants is given in Table 11 from the German “Biological WastesOrdinance”. The validation with pathogens and seeds may be regarded as “directprocess validation” it must be accompanied by continuos recording of measurableprocess data like temperature, pH, humidity etc. in order to detect deviations anddisturbances of the process over the whole year, which may result into an insufficientmicrobicidal effect. The system of process validation has to be completed by acontinuos supervision of the final product, at least twice a year.

With respect to sewage sludge, which is compared to municipal household orbiowaste a relative homogenous substrate it may be taken into consideration that those

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Table 11: Example of a validation and supervision strategy for biogas and composting plantsand the resulting products according to the german biowastes ordinance (1998).

Investigated parameter Direct validation of the Indirect process Supervision of the finalprocess supervision product

Hygienic safety - New constructed plants - Continuous Regular investigation of theconcerning risks for (within 12 month after registration of final product for hygienicman, animals and plants opening of the plant) temperature at safety2,3

- Already validated plants three representativeif new technologies locations in the have been invented or process, or if the process has responsible for thebeen significantly the inactivation ofmodified (within 12 the microorganismsmonths after invention and seeds or modification) - Recording of

- Existing plants without process data (e.g.validation within the turning of last five years before windrows, this validation strategy moisture ofwas invented (within material, starting18 months) and finishing data).

Number of test trials 2 Test trials, at open air Continuous data Continuously all over thecomposting plants at recording to be year at leastleast one in wintertime filed for at least - semi-annual (plants

five years with ≤3000 t/a throughput)

- quarterly (plants >3000t/a throughput)

Number of Human and 1 test organism – - No salmonella in 50 gtest veterinary (Salmonella senftenberg product detectableorganisms hygiene W 775,H2S-neg.)

Phyto- 3 test organisms - Less than 2 seeds capablehygiene (Plasmodiophora brassicae, of germinating

tobacco mosaic-virus, and/or reproducible partstomato seeds) of plants in 1 l of product

Number of samples – - Throughput of the plantsSample per test-trial: in t/aHuman and veterinary 241 1. ≤3000 (6 samples perhygiene 361 year)Phytohygiene 2. >3000-6500 (6 samples

per year plus one moresample for every1000 t throughput)

3. >6.500 (12 samples peryear plus one moresample for every 3000 t)

Total 60

1At small plants half the number of samples (≤3000 t/a).2Every statement concerning the hygienic safety of the product is always based on the result ofthe supervision of the final product together with the result of the validation of the process.

3Every sample is a “mixed sample” (about 3 kg) based on five single samples of the finalproduct.

physical or chemical treatment procedures which had been basically validated inscientific experiments and which had been demonstrated their reliability underpractical conditions for a long period of time may not undergo a direct processvalidation. In such cases the continues recording of the relevant process data incombination with a more frequent (e.g. monthly) microbiologicals examination of thefinal product could be sufficient. Same should apply for small plants either they usephysical, chemical or generally validated biological treatment.

Supervision of hygienic safety of the product

As mentioned above, the investigation of the final product resulting from sludgetreatment in order to detect every pathogen which may be present in the material isimpossible, therefore representative indicator organisms have to be determined fromthe point of view of human and animal health and if necessary for the purpose of safeplantbreeding and production too. Those indicator organisms must fulfil severalrequirements:• They have to be present with a high probability in the raw sludges• The transmission via sludge and sludge related products must be a factor in

epidemiology• If a biotechnical process is used, the indicator should not be involved in the process

itself• The indicator should not be an organisms which is generally present in soil and soil

related materials• The method for isolation and identification must be simple, effective and reliable if

applied to a substrate with a complex microbiological matrix as biological sludge orrelated materials.

With respect to public health and veterinary requirements several indicators andparameters are in discussion:• Salmonella• Enterococci (Streptococci of group E)• Staphylococcus aureus• Enterobacteriaceae• Escherichia coli• Clostridium perfringens• Sulfite reducing Clostridia• Entero viruses• Rotavirus• Eggs of nematodes• Larves of nematodes

Since organic sludges, compost and related products are mostly coming out of amicrobial degradation process and the knowledge about the microbiological ecologyof such materials is very limited it must be warned to use isolation and identificationtechniques common in clinical microbiology without careful validation incombination with the involved sample materials. The variety of species to be presentin environmental, samples and materials resulting from aerobic or anaerobic

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biological treatment far exceeds the limited number of species to be taken into accountin se- and excreta as well as in body fluids and the variability in species is high and notyet fully understood. Moreover microbial parameters which are used in the field ofwater-hygiene and food inspection are not applicable for substrates like stabilizedsludges or composts because most of those indicators belong to the indigenous flora ofagricultural soils (Böhm, 1995). If the limited reliability and applicability of methodscoming from clinical microbiology and water inspection for the intended field of useis taken into account as well as the fact that the exclusion of organisms whichgenerally may be found in normal soils gives no sense for a substrate and fertilizer assludge or compost the following microbial parameter are inappropriate:Staphylococcus aureus, Enterobacteriaceae, Clostridium perfringens and sulfitereducing Clostridia.

The only parameter which seems to be useful and reliable in this connection is itabsence or presence of Salmonella. Salmonella are generally found in untreatedsewage sludge with a high probability in various concentrations. Since it is known thatthe probability of identifying a positive sample is basically related to the amount ofinvestigated material a compromise between feasibility and reliability has to be found.It is proposed to investigate 50 g or 100 g (2x50 g) of compost for the presence orabsence of Salmonella with the method described in principle in the German BiowasteOrdinance using a preenrichment in buffered peptone water and an enrichment step(Edel and Kampelmacher, 1969; Rappaport et al., 1956; Vasiliadis, 1983).

Escherichia coli and Enterococci are generally present in untreated sewage sludgetoo, but they are no pathogens except certain serovars of E. coli. Those toxin formingand adhesive types as Escherichia coli 0157:H7 are extremely rare in wastewater asfound in recent investigations (Karuniawati; unpublished data, 1999). Other E. coliserovars and Enterococci may be found in the environment including soil and surfacewater as indigenous flora too. Moreover the methods described for reisolation andenumeration from environmental samples are not as reliable as for Salmonella.Nevertheless E. coli and Enterococci may be used as additional parameters withincertain limitations given by the treatment process to be supervised. Enterococci forexample cannot be used as indicator in the examination of compost and compostrelated products but for the thermophilic anaerobic treatment in biogas plants as wellas for pure thermal treatment they are very valuable (Bendixen, 1999).

Enteroviruses are generally present in sludge of fecal origin but not regularly insludges coming from other sources. In principle Enteroviruses may be used asadditional indicator but the reisolation procedure are as for all viruses fromenvironmental samples are labour- and costintensive. Their resistance in the involvedtreatment processes is not higher than that of Salmonella, this means, that theadditional informations resulting from using this indicator organisms are low. Sameapplies for rotavirus, even it is of special environmental importance according toMetzler et al., 1996 and Pesaro et al., 1999.

The question if nematodes or nematode eggs are an useful indicator in this connectionis not easy to answer. With respect to nematodes pathogenic for men and/or animalsthe experience shows that even eggs of Ascaris suum are less thermoresistant than

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Salmonella, but behave differently in chemical treatment, this means that ifSalmonella would have not survived e.g. the composting process Ascaris eggs andwith them all other nematodes eggs would not have done either. This does not applyfor treatment with slaked lime or long term storage. This means that Ascaris eggs willnot be a necessary indicator in all processes in which the thermal effect is thepredominant one but they will give valuable additional informations if used in thesupervision of all other treatment processes.

This leads to the problem of indicator organisms from the point of view ofphytohygiene if this is required. No plant pathogen virus, fungus or bacteria has beenfound until now which is of comparable importance as Salmonella for the abovementioned purpose. The only indicator which is widely distributed in biologicalwastes from households and comparable organic sludges are tomato seeds. Evenknowing that this indicator will not cover totally all requirements, it seems to bereasonable and feasible to define the term “phytohygienic safety” of the product ifnecessary as follows: The final product should not contain more than two seedscapable to germinate and/or reproducible parts of plants in 1 l. A suitable test-methodis described by Bundesgütegemeinschaft Kompost (1994).

Final remarks

The combination of certain restrictions in using sewage sludge as fertilizer and/or soilimprover in relation to the type of treatment used in combination with a system ofprocess validation and steady supervision of relevant process data as well as of thefinal product as given in Fig. 4 seems to be reasonable in order to protect farmer,consumer and the environment against hygienic threads. Even if a list of approvedtreatment processes will be given, the method for the validation of the treatmentprocedures themselves must be elaborated at EU-level.

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Figure 4: Process validation and supervision together with product supervision in order toassure hygienic safety of sewage sludge and related products deemed to be used as fertilizer orsoil improver.

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23. Hurst, C.J. (1989): Fate of viruses during wastewater sludge treatment processes. CRC Crit. Rev.Envir. Control, 18, 317-343.

24. IAEA (Internaional Atomic Energy Agency (1975): Radiation for a clean environment,STI/PUB/402, ISBN 92-0-060075-1, Vienna.

25. Köhler, B. (1993): Beispiele für die Anreicherung von Salmonellen in der Umwelt. Dtsch.tierärztl. Wschr., 100, 264-274.

26. LAGA-Länderarbeitsgemeinschaft Abfall (1995): LAGA-MERKBLATT M10. Qualitätskriterienund Anwendungsempfehlungen für Kompost, pp 1-52. In: Hösel, G., Schenkel, W., Schnurer; H.Müllhandbuch Vol. 4, No. 6856. Erich Schmidt Verlag Berlin.

27. Lessel, T. (1985): Ein Beitrag zur Optimierung des Verfahrens zur Gamma-Bestrahlung vonKlärschlamm. Berichte zur Wassergütewirtschaft und Gesundheitsingenieurwesen Nr. 54, TU,München.

28. Mayr, A. (1983): Verbreitung von Infektionserregern über Abfälle durch Haus-, Gemeinde undFreilandungeziefer unter besonderer Berücksichtigung der Gesundheit des Menschen. Zbl.Bakt.Hyg., I. Abt. Orig. 1B, 178, 53-60.

29. Menke, G. (1992): Hygienische Aspekte der Bioabfallkompostierung. Teil 1: Phytohygiene, pp68-73. In: Proc. Symposium des Umweltministeriums Baden-Württemberg und der LG-Stiftung“Natur und Umwelt”, 26. März 1991 in Stuttgart, “Bioabfallkompostierung - Chance derAbfallverwertung oder Risiko der Bodenbelastung?”. Stuttgart: LG-Stiftung “Natur undUmwelt”, Königstr. 3-5, D-70173 Stuttgart.

30. Metzler, A., Regli, W., Leisinger, M., Heider, H., Schweizer, K. und Tabisch, A. (1996): Virenund Parasiten im Trinkwasser: Risiken und Prävention. Mitt. Gebiete Lebensm.Hyg. 87, 55-72.

31. Müller, G. (1965): Die Salmonellen im Lebensraum einer Großstadt (Untersuchungen überVorkommen und Lebensdauer in der Außenwelt). Beitr.Hyg. Epidemiol. 19, J. Ambrosius BarthVerlag, Leipzig.

32. Ottolenghi, A.C. and Hamparian, V.V. (1987): Multiyear study of sludge application to farmland:Prevalence of bacterial enteric pathogens and antibody status of farm families, Appl. Environ.Microbiol. 53, 5, 1118-1124.

33. Pagon, S., Sonnabend, W. und Krech, U. (1974): Epidemiologische Zusammenhänge zwischenmenschlichen und tierischen Salmonella-Ausscheidern und deren Umwelt im schweizerischenBodenseeraum. Zbl. Bakt. Abt. I Orig. B 158, 395-411.

34. Pesaro, F., Wellinger, A. and Metzler, A. (1999): Inactivation of animal viruses duringthermohilic fermentation of source separated waste in a full scale biogas plant, pp. 62-68. IEABioenergy Workshop (Proceedings). Deutsche Veterinärmedizinische Gesellschaft e.V.,Frankfurter Str. 89, D-35392 Giessen.

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35. Philipp, W. (1981): Vergleichende hygienische Untersuchungen über die Wirkung derKlärschlammpasteurisierung vor und nach der mesophilen, anaeroben alkalischenSchlammfaulung. Vet. med. Diss., Univ. Giessen..

36. Pike, E.B. (1983): Long-term storage of sewage sludge, pp 212-225. In: A. Bruce, A. Havelaarand P. L’Hermite (eds), Disinfection of sewage sludge: technical, economical andmicrobiological aspects, D. Reidel, Dordrecht, Holland.

37. Pollmann, B., and Steiner, A.M. (1994): A standardized method for testing the decay of plantdiaspores in biowaste composts by using tomato seed. Agribiological Res., 47, 1, 27-31.

38. Rapp, A. (1995): Hygienisch-mikrobiologische Untersuchungen zum Verhalten vonausgewählten Bakterien und Viren während der längerfristigen Speicherung von Flüssigkeit inGüllegemeinschaftsanlagen. Agrarwissenschaftl. Diss., Univ. Hohenheim.

39. Rappaport, F., Konforti, N. and Navon, B. (1956): A new enrichment medium for certainSalmonellae, J. Clin. Pathol. 9, 261-266.

40. Strauch, D. (1984): Use of lime treatment as disinfection process, pp. 220-223. In: P.L'Hermiteand H. Ott (eds.), Processing and use of sewage sludge, Reidel Publ. Comp., Dordrecht.

41. Strauch, D. (1991): Survival of pathogenic micro-organisms and parasites in excreta, manure andsewage sludge, Rev. Sci. Techn. Off. Int. Epiz. 10. 813-846.

42. Strauch, D. (1998): Pathogenic micro-organisms in sludge. Anaerobic digestion and disinfectionmethods to make sludge usable as fertiliser. European Water Management 2, No. 2, 12-26.

43. Vassiliadis, P. (1983): The Rappaport-Vassiliadis (RV) enrichment medium for the isolation ofSalmonellas: an overview. J. Appl. Bacteriol. 54, 69-74.

44. Williams, B.M., Richards, D.W., Stephens, D.P., and Griffiths, T. (1977): The transmission of S.livingslone to cattle by the herring gull (Larus argentatus). Vet. Rec. 100, 450-451.

45. Wuthe, H.H. (1973): Salmonellen in einer Brutkolonie von Lachmöven. Berl. Münch. Tierärztl.Wschr. 86, 255-256.

Pros and cons of the use of sludge in agriculture as compared to animal manure, mineral fertilisers and other wastes

Michèle LegeasFrench National School of Public Health, department EGERIESAvenue du Professeur, Léon BernardF-35042 Rennes Cédex

Introduction

To introduce this paper, it is necessary to present the French National School of PublicHealth, and more accurately, the teaching department so called “EGERIES“. Theorientation of this communication depends hardly on an institutional position.This state school of further education, unique in France, takes a major part in thetraining course of sanitary engineers, physicians and pharmacists inspectors, allworking for the Public Health Ministry. All these technicians are prepared to take intoaccount risks induced for human health by the environment and the health care systemin decision making process.

So, it is clear that this paper will focus only on human health risks and not on the risksfor the environment neither an the point of view of sustainable development.

Using a risk assessment method in this debate?

For the moment, the best approach to estimate human health risks induced by aproduct or a practice is the method of quantitative environmental health riskassessment. This method is based on a four stage process:• Hazards identification,• Definition of a dose-response relationship for a hazardous substance,• Exposure assessment of a population, or a sub-group of this population,• And finally, risk characterisation, expressed as an excess of cases of sick persons

inside exposed population.

Using this method allows not only the definition of a risk for a particular product butalso the comparison of risks induced by two or more similar products. In the debatearound pros and cons agricultural use of wastewater treatment sludge in comparison toother products, this method would be theoretically the only one available. But it existsa lot of difficulties to apply it.

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Hazards identification

The purpose of this stage is to list all compounds having a well known toxic orinfective effect. Classically, the first method used to make this screening is abibliographical review. When data are not available, it s possible to make hypothesisbased on the origin of the product. The three main classes of pollutants are: heavy metals, micro-organic compounds andmicroorganisms.

Heavy metals

It is quite impossible to say exactly what concentrations of each heavy metal arepresent in various products, because the pressure of measurement is not the sameaccording to the type of product: there are few data concerning animal manure, whenthere are very numerous for sludge. It is only possible to build a table (Table 1)presenting the presence of heavy metals in the different products. In terms of publichealth, the more hazardous component is cadmium.

Micro-organic pollutants

The lack of data upon organic pollutants is very clear. It is only possible to say that,probably:• they are absent in mineral fertilisers,• in animal manure, they are numerous (animal care residues, such as antibiotics,

products for desinfection or treatment of farm buildings),

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Table 1: Presence of heavy metals, even as traces, for various products.

Mineral fertilisers Animal manure Urban sludge Composts Atmospheric depositsAs ++ + ++ ++Cd ++ + ++ ++ ++Cr ++ + ++ ++ +Hg ++ + ++ ++ +Ni ++ + ++ ++ +Pb ++ + ++ ++ ++Se ++ ++ ++ ++Zn ++ ++ ++ ++ ++Cu ++ ++ ++ ++ ++

Table 2: Medium composition (mg/kg dm)for heavy metals in mineral fertilisers andurban sludge.

Mineral fertilisers Urban sludgeAs 1,8Cd 1,6 5,3Cr 63 80Cu 334Ni 20 39Pb 7 133Hg 0,1 2,7

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• they are still more numerous in urban sludge and composts (pesticides, atmosphericdeposits, all residues of human urban activities).

Analytical progresses induce more and more indications of the presence of this type ofcomponents. The list will increase every day, but it exists little data on the toxicity ofeach one.

Microorganisms

About microorganisms, it is possible to list a large quantity of species, encountered aswell in urban sludge as in animal manure (Table 3). Quantitative data are poor onpathogenic microorganisms and concern quite only bacteria indicators of faecalcontamination.

Exposure assessment

In fact, data are not sufficient, as well qualitative data as quantitative ones. So, the stage ofexposure assessment is not possible and quantitative risk assessment cannot be achieved.

So, how to manage the risks?

If it is not possible to work out the risks, it is possible to manage them. To do that, it isnecessary to understand the ways of exposure and to characterise the exposedpopulations. Knowing that, risk prevention can be achieved by reducing the exposure.

Ways of exposure depend on the mode of agricultural use of the different products:doses, type of cultures, period of use:• mineral fertilisers (200 to 800 kg/ha/y), all cultivated soils, of which vegetables,• animal manure (1 to 3 t/ha/y), a large part of cultivated soils, large cultures,• urban sludge (3 t/ha/y), less than 10% of the soils receiving manure, large cultures.

Risks associated with these uses are:• a direct contamination of: soils, vegetables, surface waters or ground waters, and

people in contact with the products,• an indirect contamination of the feed chain.

Table 3: Pathogenic microorganisms potentially present in the products.

Urban sludge Animal manureBacteria Salmonella, Bacillus, Campylobacter, Salmonella, Bacillus, Campylobacter,

Yersinia, Leptospira, Clostridii, Vibrio... Yersinia, Leptospira, Clostridii, Brucella...Virus HVA, HVE, poliovirus, rotavirus, Norwalk Aphtovirus, Coronavirus, Herpès,

like... Parvovirus, Rotavirus...Parasites Taenia, Ascaris, Trichuris, Oxyuris, Strongiloïdes, Toxocara, Trichuris,

Giardia, Cryptosporidium... Cryptosporidium, Coccidis...Fungii presence presence

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It appears that major risks concern people working in contact with the products andthen after people eating contaminated products.

All available epidemiological data indicate that probably the level of sanitary risks islow: workers on wastewater treatment plants or on composting units do not showmore specific disease than others. Except when they have been sprinkled with rawwastewater, there are no proof of any epidemic induced by consumption ofvegetables. Furthermore, analysis of food products coming from soils receivingsludge or coming from soils receiving others fertilisers do not indicate importantdifferences.

Finally, what can be concluded about the specific risks linked to use of sludge in agriculture?

Firstly, a need of more and more knowledge. Then, a need of a serious control for thequality of sludge. And finally, a more serious need of control for this use. In fact, thatcan be summarise as ‘the cautious use of the principle of prevention’.

But, in comparison with the other main alternative, i.e. incineration, it is clear that:• it is not the same scale in terms of impact area,• it is not the same impact in terms of exposure of populations,• it is not the same impact in terms of acceptability by the population,• it is not the same impact in terms of costs• and not the same ecological interest.

In fact, it appears that this question of human risks linked to agricultural use of urbansludge, probably is not really a question of public health, but a question of socialagreement in front of uncertainties. A lot of participants involved in this field(farmers, legal authorities, communities, companies of wastewater treatment, foodindustries, environmental groups, consumers), a lot of interests, a lot of concerns..., allthe society, faced to its current model of development.

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The role of sludge on the reintegration of soil fertility

P. Sequi, F. Tittarelli, A. BenedettiIstituto Sperimentale per la Nutrizione delle PianteVia della Navicezza 2-4I-00184 Roma

Introduction

Sludges, as products obtained by wastewater treatment, contain organic matter, microand macronutrients and are potentially useful for any agriculture use. On the other hand,they may also contain undesirable organic pollutants, heavy metals and pathogens whichcan be potentially harmful. For all these reasons, the use of sludge in agriculture, atEuropean Union level, is regulated by the EU Sludge Directive 86/278/EEC. Italyenacted it into its legislation by Law Decree 99/92 (D.L. 99/92). So far, in Italy, despite achronic deficiency of soil organic matter, recycling sludge in agriculture has encounteredmany difficulties and cannot be considered a widespread agricultural practice.

In order to focus on the real contribution to the reintegration of soil fertility of sludgerecycling in agriculture, the following points should be stressed:• sustainability of sludge application to soil;• contribution of sludge to the fertility of soil as a whole (physical, chemical and

biological)• organic matter stability and quality parameters

Sustainability of sludge application to soil

The main positive aspect of sludge recycling in agriculture is probably related to thesustainability of this practice. The word “sustainable” referred to an agricultureactivity is of widespread use, even if sometimes is misused. Indeed, it is, sometimes,associated to the reduction of agrochemical inputs, or to the application of somerecent EC directive or U.S. EPA recommendation. All these interpretations are, ofcourse, misleading, because none of them consider the most important aspect of asustainable system or activity: the capability of maintaining itself for an indefiniteperiod of time. The above concept must be considered in a broadest sense: an activityor a system cannot be considered separately and isolated from other activities andsystems. The production of sludge as a consequence of wastewater treatment gives, tothe society as a whole, the opportunity of closing the cycle of nutrients: sludge derivedfrom agricultural activity must return to soil if a sustainable and ecologically soundmanagement of these materials is desirable (Sequi, 1996).

More specifically, sludge recycling in agriculture can be considered a sustainableactivity because fulfils simultaneously the following requisites stated by OCDE(1992):• to guarantee the conservation of environmental equilibria so as to allow that

productivity lasts on a permanently durable basis, i.e. it should not lead in particularto dissipation of non-renewable materials or energy (sustainability of resources);

• to guarantee full safety to the farmer and any other operator, in addition to hygienicand sanitary safe conditions to the consumer (sustainability of human health);

• to guarantee economically convenient productions, i.e. a profit to farmers(economical sustainability)

Therefore, as a conclusion of what stated above, one of the most important questionregarding soil system ability in recycling sludges is not relative to the capacity of soilsto decompose organic materials of different origin, but, among the other aspects , tothe total quantities which can be added before the system is overloaded. Too oftensludge is being viewed as a disposal problem, rather than as a resource; indeed, thisproduct could be considered as a good, cheap fertiliser and soil conditioner. The keyof sludge recycling is the knowledge of its main characteristics and the agronomicvalorisation of organic material for the improvement of soil fertility.

Sludge application to agricultural soils: a contribution to soilfertility

According to Finck (1995), soil fertility is a complex term determined by an adequatecombination of many components like soil depth, texture, soil reaction, nutrientcontent, organic matter content and composition, soil microbial activity, content orabsence of potentially toxic substances etc. The primary beneficial effect of biosolidapplication to agricultural soils is the supply of essential plant nutrients, but, ingeneral terms, it is more correct to stress that positive effects are connected totemporary and permanent induced modifications of physical, chemical and biologicalcharacteristics of soil.

Physical fertility

Improvements in soil properties such as structure (aggregation), cation exchangecapacity (CEC), water holding capacity and permeability were shown by manyauthors. Increases in soil organic carbon as a consequence of biosolid application werefound correlated with lower bulk density, higher aggregation and aggregate stabilityand water holding capacity (Cochran et al., 1997). Infiltration and hydraulicconductivity in sludge amended soil is more variable depending on time, rate and wayof application. Land application of biosolid on soil surface may reduce hydraulicconductivity, while a simple technique of good agricultural practice like sludgeincorporation leads, over time, to an improvement of water infiltration due to a betteraggregation and macroporosity.

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Less surface crusting under rainfall, reduction of soil erosion in steep slope soils,increase of water retention in sandy soils and reduction of waterlogging andcompactability of clay soils are some of the positive effects connected to sludgeapplication to agricultural soils.

Chemical fertility

The evaluation of the agronomic value for sludges is more difficult than for mineralfertiliser, because more complex is the definition of specific parameters of quality forthe estimation of benefits relative to land application of organic material whosechemical composition is so variable. As reported above, the simplest way is theevaluation of the supply of organic matter and plant nutrients, particularly themacronutrient content of N and P; in Table 1 and 2 are shown main physico-chemicalcharacteristics of sewage and industrial sludges. Crop yield response to an organicamendment, as with mineral fertilisers, follows the law of diminishing returns, so theagronomic value per unit of added material is higher to the farmer at low rather thanhigh application rates (Parr and Hornick, 1993). A key role, in the determination ofthe agronomic value of land application of sludges, is played by the quality andquantity of organic matter added. Indeed, these characteristics influence the rate atwhich organic matter mineralises in soil and, consequently, the great residual effectson soil fertility. The slow-release character of nutrient components in biosolid is

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Typology Anaerobic sludge Aerobic sludgeParameters MEAN STD MEAN STDDry matter % 20.29 8.18 22.12 12.39Humidity % 79.71 8.18 77.15 12.73Ash % 40.22 11.97 45.22 8.41Organic matter % 59.85 11.97 55.05 8.11Org. C % 30.4 7.56 26.57 3.92Total N % 4.08 1.58 3.21 1.13Total P % 0.9 0.51 2.08 1.39Total K % 0.39 0.21 0.37 0.12pH 7.42 0.41 7.1 0.66Cd mg/kg 2.52 2.07 3.86 5.06Total Cr mg/kg 414.57 355.27 113.58 76.27Hg mg/kg 21.69 29.98 0.98 0.5Ni mg/kg 164.04 248.18 76.02 50Pb mg/kg 196.53 80.44 221.11 114.68Cu mg/kg 414.18 350.49 367.09 201.23Zn mg/kg 1619.92 887.04 1228.48 576.77As mg/kg 2.82 2.15 6.51 10.19Se mg/kg – – 0.92 0.7B mg/kg – – 51.48 51.05

Table 1: Physico-chemical characteristics of sewage sludges*.

*Data expressed on dry matter basis, except dry matter and humidity that are expressed on wet weight.From: Collana Ambiente n. 10 (1997) modified.

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responsible for the increase of crop yields in subsequent years and determines thedifficulty in evaluating the true agronomic value of land application of sludge.

Nitrogen component in biosolids is probably the most interesting from either anenvironmental and an agronomic point of view and this is the reason for using Ncontent as the basis for calculating the application rates. Biosolids contain two formsof nitrogen: organic and inorganic nitrogen. Inorganic N occurs in two chemical formsNO3

- and NH4+ which can be taken up and used by plants, but can be lost in large

quantities for leaching, denitrification and volatilisation respectively. Organicnitrogen, on the other hand, cannot be easily lost in soil, but in order to be uptaken byplants must be converted by soil microorganisms into inorganic N (mineralisationprocess). At the same time NO3

--N and NH4+-N can be used by microorganisms to

produce N-containing organic compounds (immobilisation process). The balancebetween the mineralisation - immobilisation processes rate is the main feature ofnitrogen cycle in soil and the starting point for any sustainable management ofbiosolids in agricultural soils.

About 70% of total nitrogen content in sludges is organic N, while the remaining 30%is inorganic with the prevailing form of ammonia. A high percentage of inorganic

Agro- Industry1 Dairy Industry Wine IndustryConfectionery

Paper IndustryIndustryLimits

Parameter D.L. Mean SD Mean SD Mean SD Mean SD Mean SD99/92

Dry matter % 16.21 16.82 18.84 13.29 25.63 12.37 21.41 3.16 28.42 5.24105°CHumidity % 83.79 16.82 81.16 13.29 74.37 12.37 78.59 3.16 71.59 5.24Ash 650°C % 24.73 13.61 22.4 12.64 39.35 20.48 46.2 10.64 23.48 11.09Organic % 74.36 13.61 77.6 12.64 60.55 20.48 53.8 10.64 76.52 11.09matterOrganic % >20 36.47 6.95 33.87 5.97 27.29 7.46 26.44 4.78 38.98 5.75carbonTotal N % >1.5 5.41 2.26 5.26 2.94 2.78 1.00 2.16 1.33 0.86 0.65Total P % >0.4 1.12 0.76 1.12 0.25 0.72 0.20 1.46 0.18 0.14 0.15Total K %. 0.59 0.51 0.37 0.13 0.34 0.17 1.00 1.06 0.04 0.03C/N Ratio 6.74 4.93 6.44 10.62 9.81 3.04 12.24 16.92 45.33 52.09pH 7.35 1.68 7.96 0.96 7.86 1.55 7.37 0.19 7.42 0.28Total Cd mg/kg <20 0.95 0.94 0.37 0.42 0.22 0.14 0.43 0.37 0.42 0.41Total Cr mg/kg 35.2 52.02 62.54 55.94 44.12 55.63 45.64 10.16 4.23 1.94Total Ni mg/kg <300 23.31 23.06 8.92 11.32 24.29 17.23 34.95 17.04 18.33 21.14Total Pb mg/kg <750 59.49 48.57 19.96 23.51 40.14 33.07 60.81 14.78 24.63 26.01Total Cu mg/kg <1000 103.18 145.35 77.3 85.21 216.67 91.89 74.17 3.42 13.9 13.00Total Zn mg/kg <2500 620.72 560.26 176.4 59.06 488.77 367.90 251.21 96.55 103 102.99

Table 2: Physico-chemical characteristic of industrial sludges*.

Notes:*Data expressed on dry matter basis, except dry matter and humidity that are expressed on wet weight.1 Data referred to slaughter and cannery industryFrom: Collana Ambiente n.10 (1997) Modified

nitrogen (50-90%) is lost by volatilisation at spreading time and soon after. Morecomplex is the evaluation of N availability from the organic nitrogen fraction. In Table3 are reported the cumulative mineralisation of organic nitrogen at different times afterinitial application. These data can be used to adjust rates for N availability which takeinto account for any inorganic nitrogen present and N mineralised from previous yearsapplications to the same field (Miller and Miller, 1999). According to all these data, it ispossible to estimate as 50% of the total N content, the available N for sludge in the firstyear of application. The remaining part of mineralisable nitrogen will be available toplants in the following two years at a decreasing rate (Dakes and Cheremisinoff, 1977).

Phosphorus (P) is an essential plant nutrient, but the low concentration (100-3,000 mgP kg-1) and solubility (<0.01 mg P l-1) in soils, make it a critical nutrient limiting plantgrowth. Even if inorganic phosphorus has generally been considered the major sourceof plant-available P in soils, the mineralisation of labile organic P was demonstratedto be important in both low and high fertility soils and soil microbial biomass to playan important role in P cycling (Tate et al., 1991).

Sludges contain on average 1% P and, generally, at the application rates determined tosatisfy crop nitrogen need, is sufficient to cover P plant uptake. After application tosoil, P is distributed in the most superficial layer (0-30 cm) as total P, while, at higherdoses, available P increases at 0-45 cm (Genevini and Mezzanotte, 1987). Main part ofphosphorus in sludges is in the form of Al, Fe and Ca phosphate not available to plants.As a consequence of the wastewater treatment, sludges are usually characterised bylow content of potassium and its contribution to plant nutrition is negligible.

Biological fertility

Due to their peculiar physico-chemical characteristics, sludges represent a perfectsubstrate for the growth of many different microbial groups (Benedetti, 1995). Sludgemay contain pathogens like bacteria, viruses, fungi and parassites, but also a hugeamount of saprophytic microorganisms belonging to the physiologic groups ofcellulolytic, pectinolytic, proteinolytic, nitrifiers and so on. Moreover, saprophyticmicroorganisms (up to 1012 cell g-1 dry matter) represent a supply of easilymineralisable organic carbon and nitrogen for soil microbial biomass.

The variety and complexity of physico-chemical and biological components inbiosolids and in soil system affects the possibility of studying the effects of organicmaterials addition to soil. Indeed, it is difficult to distinguish between the direct andthe indirect effects of an amendment on soil microbiological activity. In sludgeamended soil, soil respiration can be stimulated as a consequence of the additioneither of labile organic matter which increases autochthonous microbiological activityand of the microbiological activity of heterotrophic microorganisms introduced withsludge. Organic nitrogen compounds are mineralised according to the samemineralisation pattern shown for organic carbon, since in most of the organic nitrogencompounds C-N are covalently bound. On the other hand, in organic compoundscontaining sulphur and phosphorus, S and P atoms are released by a simple enzymatichydrolysis without a specific organic matter mineralisation process.

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As stated above, if labelled materials are not used, it is still difficult to determine ifmineralisation products like CO2, NH4

+, SO4--, PO4

--- derive from the mineralisationof native organic matter or added organic material.

Organic matter stability and quality parameters

In the previous paragraphs, the key role played by organic matter in determining soilfertility in a broad sense was underlined. In order to manage in a sustainable way the hugeamount of sludges produced every year in modern society, the most advisable option is toclose the cycle of nutrients by applying residual organic material to soil. This option isnecessary, but not sufficient to reach the proposed aim. Indeed, it is indispensable thatapplication to the soil of organic materials be agronomically effective. To make a positivecontribution to the organic matter balance, the most important parameters to be evaluatedare the organic matter content and its stability. Two major tasks are then imperative inorder to evaluate the quality and optimise the use of organic residues in agriculture. Thefirst is to assess the actual stage of the "maturation" of organic amendmentsquantitatively, so as to improve the transformation processes and to be able to utilise theamendments at the proper time. The second is to distinguish qualitatively the organicmatter from different sources, so that unknown materials could be recognised.

The use of selective chromatographies on solid PVP has been suggested to separatehumified from nonhumified materials in the extracts from a range of sources includinganimal refuse (Sequi et al., 1986; Ciavatta et al., 1988). A scheme of the proposedprocedure is represented in Figure 1. The use of solid PVP is now officially required byItalian law for characterization of some organic amendments (peat, leonardite and humicextracts). The fractionation scheme of organic extracts is very simple, and identical fordifferent matrices (soils, organic fertilizers and amendments, etc.). The separation ofhumified from nonhumified (NH) materials is achieved by precipitation of humic acid(HA) at a low pH value and loading of the soluble fractions on columns packed withinsoluble PVP. Nonhumified materials (NH) are not retained on PVP; after washing with0.01N H2SO4, the fulvic acid (FA) fraction is eluted with 0.05N NaOH and added to thehumic acids. This procedure has been applied with good results on organic amendments,and also used to follow the maturation of organic matter in a range of waste materials.

Cumulative N mineralized afterMaterial Year 1 Year 2 Year 3

% % %Poultry manure 80 82 83Biosolids (anaerobis) 20 30 35Biosolids (aerobic) 15 25 30

Table 3: Cumulative mineralization of organic N in a variety of by products at several timesafter initial application.

From: Miller and Miller (1999) modified.

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Three parameters of humification have been proposed:

1 - humification index (HI)HI = NH/(HA+FA)i.e., the ratio between nonhumified (NH) and humified (HA+FA) compounds;

2 - degree of humification (DH)DH% = [(HA+FA)/TEC] • 100i.e., the percentage of humified compounds with respect to total extracted carbon(TEC);

Figure 1: Separation of humified (HA + FA) from non humified materials (NH) by means ofcolumns packed with insoluble PVP. Non humified fractions are not retained on PVP; afterwashing with 0.005 M H2SO4 the fulvic fraction is eluted with 0.05 NaOH and added to humicacids. After Ciavatta et al. (1990).

3 - humification rate (HR)HR% = [(HA+FA)/TOC] • 100i.e., the percentage of humified compounds with respect to total organic carbon(TOC) in the sample.

Although the above methods have been proven to be useful for evaluating theevolution and the stabilisation of organic matter from a quantitative point of view incomposting and in sludges aerobically treated (Govi et al., 1995; Ciavatta et al., 1988,De Nobili et al. 1989, Tittarelli et al., 1998), during the anaerobic digestion the valuesof DH, HR and HI appear not to follow a definite trend (Tables 4, 5, 6) (Govi et al.,1995; Collana Ambiente n. 10, 1997). Even if D.L. 99/92 individuates only the degreeof humification as chemical parameter for establishing the stability of organic matterin sludge, the use of biological essay of organic matter stability (phytotoxicity essay,respiration index, nitrogen mineralisation index) could be useful when chemicalparameters do not furnish unambiguous results.

Chemical methods reported above are able to evaluate organic matter stability from aquantitative point of view, but cannot distinguish qualitatively organic matterextracted from different sources.

A technique which is giving interesting results on the qualitative characterisation ofthe organic matter and, in addition, seems to be a fast and reliable technique tocharacterise the stage of maturation of organic matter is Isoelectric focusing (IEF). Itis based on the electrophoretic separation of amphoteric substances on a pH gradient

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Plants ALBA CUNEO ALESSANDRIAB E B E B E

Humidity % on such 97.9 70.9 98.2 83.4 95.8 66.9Organic matter % 59.4 40.4 65.7 63.2 66.0 54.8Org. C % 29.7 20.2 32.8 31.6 33.0 27.4Ash % 40.6 59.7 34.3 36.8 34.0 45.3pH % 6.6 8.3 6.4 8.2 6.1 8.4Total N % 4.9 3.2 0.8 5.0 2.5 4.4T.O.C. % 31.2 18.0 37.3 31.2 41.2 24.5C/N % 6.3 5.6 48.4 6.3 16.8 5.6Total P % 1.4 1.8 1.8Total K % 0.3 0.2 0.3T.E.C. % 21.3 11.0 21.0 19.3 28.0 13.3HA+FA % 15.5 8.8 15.4 13.7 20.5 9.1NH % 5.8 2.2 5.6 5.6 7.5 4.2DH % 72.8 80.4 73.5 71.1 73.3 68.2HR % 49.7 48.8 41.4 44.0 49.8 37.0HI 0.4 0.2 0.4 0.4 0.4 0.5

Table 4: Physico-chemical characteristics of sludges at the beginning (B) and the end (E) ofanaerobic treatment*.

*Data expressed on dry matter basisFrom: Collana Ambiente n.10 (1997) modified.

128

Plants ASTI FOSSANOB E B E

Humidity % on such 99.64 93.66 99.66 87.01Organic matter % 69.53 74.64 67.55 72.91Org. C % 34.77 37.32 33.77 36.46Ash % 30.47 25.36 32.45 27.09pH % 7.3 7.2 7.15 8.1Total N % 5.84 6.46 5.99 2.48T.O.C. % 36.28 36.66 33.74 34.26C/N % 6.21 5.67 5.63 13.81Total P % 1.65 1.77Total K % 0.48 0.44T.E.C. % 21.95 25.56 23.7 25.91HA+FA % 12.01 16.52 12.33 18.07NH % 9.94 9.04 11.37 7.84DH % 54.72 64.63 52.03 69.74HR % 33.1 45.06 36.54 52.74HI 0.83 0.55 0.92 43

Table 5: Physico-chemical characteristics of sludges at the beginning (B) and the end (E) ofaerobic treatment*.

*Data expressed on dry matter basisFrom: Collana Ambiente n.10 (1997) Modified

Table 6: Total extracted carbon (TEC), humified carbon (HA+FA) and humificationparameters of the materials studied.

Sample TEC (%DM*) HA+FA (%DM*) HR (%) DH (%) HID1 7.1±0.3 a 3.3±0.6 a 12.2 46.5 1.15D2 5.4±0.5 b 2.1±0.3 b 8.1 40.0 1.57D3 5.7±0.6 b 2.6±0.3 b 10.8 46.0 1.19C1 8.9±0.6 a 5.1±0.3 a 19.8 56.5 0.78C2 8.3±0.7 a 5.2±0.4 a 24.6 62.9 0.60C3 5.8±0.5 b 3.9±0.3 b 18.3 66.7 0.49

*DM=Data expressed on dry matter basis. Data within each column followed by the sameletter are not significantly different at the P=0.05 probability level.

D1 = sample taken from anaerobic digesterD2 = sample taken from anaerobic digester and then stabilised anaerobicaly in thickening beds

without any treatment for 5 daysD3 = sample taken from anaerobic digester and then stabilised anaerobicaly in thickening beds

with the addition of polyelectrolites, followed by concentration through a filter press andthen stabilised for 20 days

C1 = sample taken from a raw mixture of sewage sludge and strawC2 = sample taken from the same mixture after 40 days C3 = sample taken from the same mixture after 80 days

From: Govi et al. (1995)

created by ampholites dissolved in the gel plate. The final result is that all themolecules of an unknown mixture are separated according to their isoelectric point ina gradient of pH. Isoelectric focusing was initially applied to aquatic humic substances(Gjessing and Gjerdhal, 1972) and on soil humic substances (Ceccanti and Nannipieri,1978). Afterwards, this technique was used for evaluating organic matter in fertilisersand soil conditioner (De Nobili et al., 1989; Govi et al., 1995) and for the detection ofcommercial fraud in fertilisers production (Alianiello et al., 1999). In figure 2 and 3are reported Isoelectric focusing profiles of different organic materials (peat, organicfertilisers, agro-industrial sludges). Even if some of them are extremely characteristicsand easily recognisable (i.e. peat), the technique has not been yet sufficientlydeveloped for identifying qualitatively different organic matrices.

129

Figure 2: Isoelectric focusing profiles of different organic materials.From: Alianiello et al. (1999) modified.

130

Conclusions

Sludges, for their organic matter and nutrients content, should be applied toagricultural soils. Land application of biosolids contributes to the sustainability ofmodern agricultural production system and must be considered as a resource foragriculture. Therefore, it is necessary that their use in agriculture is not realisedaccording to a disposal attitude, but in the framework of an efficient agronomic use ofavailable organic material.

The challenge is to define the best and safest quality parameters according to theagricultural use of sludge at an European level, keeping an eye on the needs ofEuropean agriculture as a whole.

Figure 3: Isoelectric focusing profiles of:A: Sludge from ice-cream production factory B: Sludge from citrus processing factoryFrom: Alianiello F. (personal communication).

References

Alianiello F., Dell’Orco S., Benedetti A. and Sequi P. (1999) Identification of primary substrates inorgano-mineral fertilisers by mean of Isoelectric Focusing. Commun. Soil Sci. Plant Anal. 30 (15 &16), 2169-2181.

Benedetti A. (1995) La sostanza organica e l’azoto dei fanghi di depurazione delle acque: effetto sullafertilità chimica e biologica. In Aspetti tecnico-economici, agronomici, pedologici, igienico-sanitari enormativi dei fanghi di depurazione civile. A cura di Ottavi C., Ottaviani M. e Figliolia A., RapportiISTISAN 95/38 (ISSN 1123-3117): 114-127.

Ceccanti B. and Nannipieri P. (1978) Concerning the reliability of Isoelectric focusing technique toseparate the soil humic substances. In: Recent developments in Chromatography and Electrophoresis.Eds. Frigerio A. and Renoz L.; vol. 10 Elsevier, Amsterdam, The Netherlands.

Ciavatta C., Govi M., Vittori Antisari L. and Sequi P. (1990). Characterization of humifiedcompounds by extraction and fractionation on solid polyvinylpyrrolidone. J. Chromatogr. 509:141-146.

Ciavatta C., Vittori Antisari L. and Sequi P. (1988). A first approach to the characterization of thepresence of humified materials in organic fertilizers. Agrochimica 32:510-517.

Collana Ambiente n. 10 (1997) Impiego in agricoltura dei fanghi di depurazione. Regione Piemontepp.141.

Cochran R., Miller W., Morris L., (1997) Decomposition of pulp mill biosolids and effects on soilproperties. Agron. Abstr. p. 275.

Dakes G., Cheremisinoff P.N. (1977) Land application of municipal sludge - water and sewageWorks R. 38.

Decreto Legislativo 27 gennaio 1992 n. 99. Attuazione della direttiva 86/278/CEE concernente laprotezione dell’ambiente, in particolare del suolo, nell’utilizzazione dei fanghi di depurazione inagricoltura. Supplemento ordinario alla Gazzetta Ufficiale, Serie Generale n. 38.

Direttiva del Consiglio 86/278/CEE del 12 giugno 1986 “concernente la protezione dell’ambiente, inparticolare del suolo, nell’utilizzazione dei fanghi di depurazione in agricoltura. Gazzetta Ufficialedelle Comunità Europee del 4/7/86 Nr. L 181/6.

De Nobili M., Cercignani G., Leita L., Sequi P. (1986) Evaluation of organic matter stabilisation insewage sludge. Comm. Soil Sci. Plant Anal., 17, 1109-1119.

De Nobili M., Ciavatta C., Sequi P. (1989) Evaluation of organic matter stabilisation duringcomposting by means of humification parameters and analytical electrofocusing. In Proceedings ofthe international Symposium on compost: Production and Use. S. Michele all’Adige (Italy) 328-342.

Finck A. (1995) Management techniques of organic materials in sustainable agriculture. In: R. Dudaland R.N. Roy (Ed.). Integrated plant nutrition Systems, report of an expert consultation. Roma, Italy13-15 December 1993. FAO Fertilizer and Plant Nutrition Bullettin, 12:139-154.

Genevini P.L. and Mezzanotte V. (1987) Uso e riciclo delle biomasse in agricoltura. CUSL.

Gjessing E.T and Gjerdhal T. (1972) Electromobility of aquatic humus: fractionation by the use ofthe isoelectric focusing technique. In: Proceedings of the International Meeting of Humic Substance,Nieuwersluis, Wageningen, The Netherlands; 31-51.

Govi M., Ciavatta C., Gessa C. (1993) Evolution of organic matter in sewage sludge: a study basedon the use of humification parameters and analytical electrofocusing. Biores. Technol. 44, 175-180.

Govi M., Ciavatta C., Montecchio D., Sequi P. (1995) Evolution of organic matter duringstabilization of sewage sludge. Agr. Med. vol 125, 107-114.

Miller D.M. and Miller W.P. (1999) Land application of wastes. In Handbook of Soil Science, Editorin Chief, Malcolm E. Sumner 9: G217 - G245.

131

132

OCDE. 1992. Séminaire sur les technologies et pratiques d'une agriculture durable. ACTEURS ETFACTEURS DE CHANGEMENT. Compte rendu du Séminaire OCDE sur le technologies etpratiques d'une agriculture durable. 11-13 février 1992. OCDE/GD (92), 49: 1-19.

Parr J. F. and Hornick S. B. (1993) Utilization of municipal wastes. In Soil Microbial Ecology.Applications in Agricultural and Environmental Management. Edited by F. Blaine Metting, Jr. 19:545-559.

Sequi P. (1996) The role of composting in sustainable agriculture. In The Science of Composting. DeBertoldi M., Sequi P., Lemmes B., Papi T. (eds.) Glasgow UK, Blackie Academic & Professional,part I; 23-29.

Sequi P., De Nobili M., Leita L. and Cercignani.G. (1986). A new index of humification.Agrochimica 30:175-179.

Tate K.R., Spier T.W., Ross D.J., Parfitt R.L., Whale K.N., Cowling J.C. (1991) Temporal variationsin some plants and soil P pools in two pasture soils of different P fertility status. Plant Soil 132:219-232.

Tittarelli F., Dell’Abate M.T., Piazza P., Varallo G (1998) Effect of fly ash addition on organic matterstabilisation of composts. Proceedings of 16th World Congress of Soil Science, Symposium 40,Montpellier 20-26 August 1998.

Possitive effects of organic matter and nutrients on crops grown on sludge amended soils

José Mª GómezBeta Nutror, S.A.Federico Salmón 81°E-28016 Madrid

A glance on Earth

(Arthur Thompson, Natural Science professor at Aberdeen University, 1920)

“What we would think of an astronomer who kept to his spectroscope and neverenjoyed the splendour of the starry strewn sky?”

Overwhelming the Earth (From “State of the World 99”, Worldwatch Institute)

“Rapa Nui (Easter Island) was one of last places on Earth to be settled by humanbeings. First reached by Polynesians 1,500 years ago, this small island 3,200kilometers west of South America supported a sophisticated agricultural society bysixteenth century.

Easter Island has a semiarid climate, but it was ameliorated by a verdant forest thattrapped and held water. Its 7,000 people raised crops and chickens, caught fish, andlived in small villages. The Easter islanders legacy can be seen in massive 8-meter-high obsidian statues that were hauled across the island using tree trunks as rollers.

By the time European settlers reached Easter Island in the seventeenth century, thesestone statues, known as “ahu”, were the only remnants of a once impressivecivilization- one that had collapsed in just a few decades.

As reconstructed by archaeologists, the demise of this society was triggered by thedecimation of its limited resource base. As the Easter Island human populationexpanded, more and more land cleared for crops, while the remaining trees wereharvested for fuel and to move the “ahu” into place. The lack of wood made itimpossible to build fishing boats or houses, reducing an important source of proteinand forcing the people to move into caves. The loss of forests also led to soil erosion,further diminishing food supplies. As pressures grew, armed conflicts broke outarmong villages, slavery became common, and some even resorted to cannibalism tosurvive.

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As an isolated territory that could not turn elsewhere for sustenance once its ownresources ran out, Easter Island presents a particularly stark picture of what canhappen when a human economy expands in the face of limited resources.

For us, the key limits as we approach the twenty-first century are fresh water, forests,soils pre-desertic lands, oceanic fisheries, biological diversity and the globalatmosphere...”

A glance on Earth

All scientifical disciplines and methods are highly valuable if we want to understandthe Universe and life on Earth but its addition does not make the big picture:• Booming of demography,• Steep increase in Economy (in terms of Gross World Product),• Climatic change and rising temperature on Earth surface,• Scarcity of water, minerals and fossil resources,• Accelerated destroy of forests and losses of soil,• Decline of the biodiversity.

Today we have more accumulated knowledge and information than ever but at thesame time is more destruction happening now to human cultures and natural systems.

This does not mean that activities of most of people are destructive but the finaleffects of our economy driven way of life.

For us scientists, entrepreneurs or regulators involved in environment and wastemanagement our primary goal is to keep in mind the big picture and understand wherethe destructive effects come from.

Sludge in cycle of life on Earth

Life’s cycle on earth

Human and in general animal life upon the earth directly depends on vegetal life andcultivated plants to survive (through vegetal direct consumption or through animalsfeedstocks).

The vegetal production vitally depends on four factors:• Soils,• Mineral nutrients,• Water coming from rain or irrigation systems,• Energy coming from sun.

Demographic growth and western economic model (fossil fuel based, automobilecentered, throaway consumption ) seriously menace these vital resources:• Soil scarcity , soil losses through erosion, natural disasters and contamination

(Every 25 years 4% of total soil potentially productive will be lost because ofurbanization processes. Other problems specially important in Africa and Brazil

134

related to acid lixiviated soil, organic matter, Ca and nutrients leaching. Estimatedevolution of “Cultivated surface per capita rate” was from 0,23 has in 1950 to 0,12 hain 1988 and estimated 0,06 ha in 2025, with terrific differences between world regions).

• Water scarcity and contamination(36% agricultural production directly depends on or irrigation system, just whenneeding to cut back importants amounts of these water diverted from rivers and pumpedfrom underground for irrigation purposes to be dedicated to human consumption).

• Limitation and exhaustion of mineral resources and fossil energies(Used for fertilizers production and other industrial uses).There is an urgent need to replace the current economic model based on naturalresources depletion for one based on renewable energy and that reuse resources andrecycles materials.

A sustainable economy

A sustainable economy will respect the following principles:• The fish catch does not exceed sustainable yield of fisheries,• The water pumped for underground aquifers does not exceed aquifers recharge,• Soil erosion does not exceed the natural rate of new soil formation,• Tree cutting does not exceed the planting and natural rate of forests formation,• Carbon emissions does not exceed the capacity of naturally fixed CO2,• Not destroy plant and animal species,• Do not increase level of contamination in soil,water or air.

135

136

Sustainable agriculture will pay attention primarily to water and soil protection andconservation, avoiding soil erosion and degradation, and also care for the eco-effientuse of resources (water, energy, machinery, fertilizers and amendments and soillabours) in a frame of environmental respect.

In a sustainable society “Quality of nature” would be priorized over “Economy andQuality of life” in western way of thinking.

Sludge and sustainability

When proper sludge products quality attained and recycling is feasible manyobjectives connected with sustainability are accomplished:• Soil economy and recovery eliminating landfill disposal and contributing torangelands restoration,• Eccoeffient use of resources through promotion of soft technologies (Quality ofnature vs Quality of life),• Mineral nutrients savings through recycling and mineral fertilizers replacement,• Fossil fuel energy savings through mineral fertilizers replacement,• Nature’s protection through reduction of fertilizers production,• Erosion control and increase of soil fertility and productivity.

Sludge/biosolids generation Spain and EU-15 (1996-2000)Residuals (000 t/y) 1996 2000Sludge/biosolidsSpain 528 1.000UE-15 6.500 8.900ManureSpain 80.000UE-15 1.020.000 8.900Solid wasteSpain 6.600UE-15 60.000

Earth cultivated surface (000 Km2)Total Planet Surface 51.310.000.000Ocean, Water, Iced surface 14.900.000.000 (29%)Earth surface 37.410.000.000 (71%)Cultivated surface 5.131.000.000 (10%)Potentially future cult surface 4-8.000.000.000 (–)

137

Sludge: residue or natural resource?

The answer to the question of utilization of sludge in agriculture (or other soilapplications) may come from finding a balance between two opposite problems:• Contamination or pollution of soils and water bodies,• The exhaustion of natural, biological and mineral resources (the soil as a complex

resource minerals as phosphate rock and fossil energy materials).

We must look at chemical fertilizers as limited resources coming from limited mineralores (phosphate, potash) or fuel and energy consuming processes (N, P, etc).

At that point that for example U.S. Department of Agriculture has recomended tofarmers in USA a policy of phosphates storage in soil, in prevision of a shortage of Psupply in some decades, following at the same time a strategy looking for control ofphosphate mines worldwide.

Agriculture in general is blamed for being the first cause of some importantenvironmental problems, many of them caused by poor quality or unproper use ofmanures, agrichemicals, fertilizers or recycled urban organics:• N and P contamination and eutrophication of water bodies (rivers, lakes and marine

areas),• Residues of pesticides in soils, water bodies and foods.

Because its nature and properties sludge could be considered a natural resource if abroad range of industrial pollutants are prevented to reach urban wastewater.

World yearly primary productionDry material production 1015 g/yearTotal primary prodution on the land area of the Earth of which: 117.5 = 100 per centPlant cultivation 9.1 = 7.7 per centGrassland 20.0 = 17.0 per centForests 79.9 = 68.0 per cent

Cultivated surface per capita (ha)World Region 1964 1984 1989World 0.44 0.33 0.28Noth America 1.05 0.90 0.86South America 0.49 0.45 0.41West Europe 0.31 0.25 0.24East Europe and CIS 0.84 0.71 0.67Africa 0.74 0.35 0.31Middle East 0.53 0.35 0.30Far East 0.30 0.20 0.14ACP 0.17 0.10 0.08

World Comision (1987), FAO (1992a).

138

Hundreds million sludge tons have been recycled and soil applied, obviously in developedcountries and agricultures, due to users acceptance and perception of advantages overtraditional mineral fertilizers application, mainly in arid areas and climates.

As already demonstrated in many cities and operations clean sludges could be producedmaking negligible water, soil o crops contamination of any kind. As any otheragricultural input, the respect of good application practices will close the loop ofsludges/biosolids beneficial use.

Post-treated sludges as “Lime stabized”, “Composted” or “Thermally dried” sludgesradically improve the sludge recycling conditions, naturally minimizing at a time itsrisks and inconvenients:• Reducing the undesirable impact of wet sludge high dosage common application

practices in short radios from Waste Water Treatment Plants (WWTPs),• Adjusting dry matter and nutrients applied to agronomical rates,• Reducing the volume to be managed by 1/3 to 1/5,• Improving dry content, aspect, reducing odour and insects attraction,• Making possible primary stocking, trucking, indoor storage, biological enhacement,

blending, bagging and soil application in safe and commercial conditions,• Reaching safe standards of microbiological quality,• Attaining marketable conditions and quality.

If sludge has convenient control, chemical quality and adequate post-treatment sludge by-products are ready to be considered as a resource (no matter if called organic or alkalineamendment, compost or organic-mineral fertilizer), able to comply with fertilizers or soilprotection quality standards and more environmentally friendly that the majority ofelaborated products (mineral fertilizers, peat moss, etc) from a life´s cycle perspective.

There is a need to promote sludge quality and post treatment and open a legislativeand political road to safe sludge recycling. Otherwise there would not be motivationfor sludge producers to improve and comply and no reward for water quality policies,with a negative environmental impact. Public administration, WWTPs operators,recyclers, farmers and society in its ensamble would benefit of a possitive simplifiedway of solving this problem.

Current sludge aplication practices

Sludge land application practices/Dosis (t/ha)

Type of sludge Application objective Wet dosis Dry matterLiquid (4% d.m.) Organic amendment 450-1000 18-40 Dewatered (25% d.m.) Organic amendment 50-100 12,5-25Composted/Lime es (65% d.m.) Org-min-alk amendm 4-8 2,6-5,2Thermal dried (90% d.m.) Org-min fertilizer 2-5 1,8-4,5

139

Nutrients effects on crops

Illustrating the need for sharp adjusted nutrients supply to the cultivated plants toobtain optimum economic, environmental and productive conditions.

P and K species in cultivated soils

Illustrating the very high levels of P and K in Spanish cultivated soils in nonabsorbable species for plants and the need for the enhancement of microbiologicaland fertility conditions for optimum economic, environmental and productiveconditions.

Sensitive areas to water pollution in EU

Illustrating the wide EU areas with ground or coastal water declared sensitive to N, P,or organic pollution.

Table: Beneficial and negative effects of sludge use.

Sludge/biosolids application – Beneficial effectsBeneficial effect ConditionsAgronomical Agronomical- Organic matter rise in soils - Significant in higher doses (direct land

application)- Humus generation (Isohumic - Idemcoefficient = 0.2)

- Increase water retention capacity - Idem- Soil structure improvement - Idem- pH correction thanks to Ca Mg content - In sandy low textured soils- Supply of slow release nitrogen - Balanced mineral-organic-alkaline

supplies- Supply of phosphorus - Avoiding low pH soils, very rainy climates,

P in groundwater- Supply of microelements (Fe, S, Zn....) - Appropiate at compost agronomical rates- Increase of crops yields: economic profits - Compost at agronomic economical ratesEnvironmental- Substitution of mineral fertilizers- Mineral nutrients recycling (Importance of P)- Slow release nutrients- Avoiding costly landfilling or incineration disposal options

140

Biosolids application – Negative effectsNegative effect Conditions- Nitrogen/Nitrates contamination of - Repeated biosolids application many yearsgroundwaters High Nitrogen content in crops on the same land(mainly forages) - Biosolids applications over agronomic rates

- Liquid or dewatered biosolids applications≤4-25% d.m.

- When agronomical rate applications, selection of adequate application periodaccording to climatic, vegetative conditionsof the culture

- Rise in heavy metals concentrations in soils - When high cumulative doses, soil high levels- Metals uptake by crops - When high cumulative doses, soil high

levels, pH <6- Increase in salts, conductivity - Specially in dry climates, drougth conditions

normally no problematic if biosolids areapplied at agronomical rates

- Adding human or animal pathogens - Untreated, not controlled sludges, unproperculture or period

- Excess quantities of some nutrients could be - Determination of agronomic rate foradded (N, P) and nutrient imbalances in the biosolids application programs, balancingsoil may occur. nutrients additions with nutrients extractions

of the soil- Limiting P levels (Bray P1 test available≤150 mg/Kg)

Type of sludge Objective Mode of application Dosis (t/ha)(% dry matter) Wet basis Dry basisLiquid Soil reclamation Whole surface application 150-1000 6-40(Range 2-6%; Average 4%) Forest plantation Whole surface application 150-1000 6-40

Organic amendment Whole surface application 6-40Dewatered(Range 18-35%; Average 25%) Soil reclamation Whole surface application 50-150 12,5-37,5

Organic amendment Whole surface application 12,5-37,5Composted Forest plantation Application in plantation 4-12 2,6-7,8(Range 60-75%; Average 65%) Gardening holes 20-40 13-26

Organic amendment Whole surface or localized 4-8 2,6-5,2Thermally dried Forest plantation Application in plantation 3-8 2,7-7,2(Range 85-95% ; Average 90%) Gardening holes 10-15 9-13,5

Organic mineral fertilizer Whole surface or localized 2-5 1,8-4,5

Table: Usual Biosolids/sludge land application practices

141

Sludge application agronomic trials

Water Environment Research Foundation Report on Biosolids long termapplication programs in USA

• Long term biosolids application programs, operating 9 to 23 years.• Land application programs with cumulative loadings equivalent to more than 600

years of continous annual agronomic rates (3-10 t dm/ha year), have shown verylittle or no impact on soil and plant systems and water resources.

• Some increases in metals (Cd and Zn especially) were found in plant tissues in someexperiences.

• Accumulation of metals in the soil was observed only in first 25 cm of topsoil.• Increased nitrate concentrations could be detected in groundwater near some

biosolids application sites in humid climates (similar to levels below manured orminerally fertilized fields).

• In Yuma (Arizona) 26% reduction in the irrigation requeriments of crops grown onbiosolids amended soils.

• High nitrate nitrogen concentrations have been observed in forages where biosolidsloadings were excessive, even being toxic to animals fed with it (As also was foundin other experiences with animal manures). Low ligth intensity and droughtconditions increase the concentration of nitrate nitrogen in plants.

• Detailed data in the following Tables.

142

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143

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a to

tal

CIT INIA field trials in SPAIN

(CIT INIA-Ayuntamiento de Madrid-SUFISA, Manuel Bigeriego, Ingrid Walter yMiguel Angel Porcel)

• Trials on corn, tomato, pepper, tobacco and vineyards

• Period of trials: 1990-today

• Program objective: Evaluate biosolids compost agronomic quality consideringagronomical and economical results in comparaison to traditional mineral fertilizerspractices in different cultures all over Spain.

• Full scale of trials with minimum plots size of 1 ha with repeated treatments everyyear.

• Trials planning following the scheme:– 1. Tradicional mineral fertilization.– 2. Only biosolids compost application.– 3. Biosolids compost (4-12 t/ha) + nitrogen in cover.– 4. control plot, no fertilization.

• Resultsa) Best results with Plot 3, biosolids compost combined with nitrogen in cover.

a1) Corn: with treatment 3, grain production always increases over treatment 1 by 3,8%, 6,2%, 7,2%, 7,4%, 14,4%, y 18,4%.

a2) Tomato: with treatment 3, production increases between 6,5% and 9,7% overtreatment 1.

a3) Pepper: with treatment 3, production increases of 9,9% in fruits and 23,6%in vegetative parts, over treatment 1

a4) Tobacco: with treatment 3, production increases between 15 and 230% overtreatment 1.

b) Extension of vegetative cycles in almost all cultures and conditions.

c) Remarkable increase in productions on crops grown on biosolids compost whensoils are poorer, sandy or extremely alkaline (like tobacco or vineyards).

d) Increased productions and improved vegetative crops behaviour due to biosolidscompost side effects (slow release of nutrients, organic matter, biologicalactivity, Fe, S, Mg supplies, etc).

Sludge applied on pastures grown on acidic poor soils in Sydney (Australia)

(D.L. Michalk, I.H. Curtis, J. Seaman, C.M. Langford and G.J. Osborne New SouthWales Agricutural Office)

• Sludge composition 32 ppm Cd156 ppm Ni872 ppm Cu

• Soil characteristics Poor soils, light texture, sheep pastures, pH= 4.7

144

145

• Trials 1. Control, 2.5 T/ha lime plus 650 kg/ha superphosphate2. N viro 7.5 T/ha3. Biosolids 30 T/ha4. 60 T/ha5. 120 T/ha

• Results

- Metals increases in pastures in different speciesZn............25 to 200 mg/kgCd ...0.1-0.5 to 0.5-2.0 mg/kgNi.....0.5-2.0 to 4.0-10 mg/kg

- Animal productionsNo milk quality variations between sheep milk in different plots.Ni increases 0,15 mg/kg to 0,45 – 1,0 mg/kg in sheeps liver, kidney, muscles, in 60and 90 t/ha biosolids amended plots.

- Metals leaching in soilsZn, Cu, Cd leachate down under 30 cm topsoil layer due to sandy acidic soil.No ground water contamination detected in any plot.

- Agronomic results60 t/ha maximizes benefits from organic matter and nutrients on soils and pastures,and minimizes environemental pollution and spoilage of livestock products.

Eleven years of biosolids application to dryland winter wheat in Colorado (USA)

(Adams County, Colorado USA; K.A. Barbarick, J.A. Ippolito, D.G. Westfald, and R.Jepson. Colorado Agricultural Experiment Station; Colorado State University)

• Soil and cultivation characteristics.Loamy soil, pH 6.5-7.8Arid dryland, Cultivation: Red winter wheat

• Five years of repeated application.1.Control no fertilizer2. 67 kg/ha mineral N3. Biosolids 6.7 t/ha (50% dm)4. 26.8 t/ha (50% dm)

• Agronomical and environmental results- Better grain yields with 67 kg/ha mineral nitrogen and 6.7 t/ha applications.- Five applications of 26.8 t/ha biosolids resulted in significantly higher NO3-N

concentrations at 10 to 125 cm soil layers than the 67 kg/ha N plot resulting in aNO3- N leachate and groundwater contamination increased risk. No problem at a6.7 t/ha agronomic rate application.

- Light increase in Cu, Ni, major increase in Zn concentrations in grain,proportionals to biosolids increased dosages. WERF Long Term BiosolidsApplication Programs.

146

The effect of selected biosolids and N rates on harvest soil nitrate-N, 1991-92, West Bennett B plots.

The effect of selected biosolids and N rates on harvest soil nitrate-N, 1991-92, East Bennett B plots.

147

The effect of selected biosolids and N rates on harvest soil nitrate-N, 1991-92, West Bennett A plots.

The effect of selected biosolids and N rates on harvest soil nitrate-N, 1991-92, East Bennett A plots.

148

Problem analysis: cadmium in sludge and soils

Different sources of heavy metals added to soils in Europe

Main sources of cadmium added to soils in Europe

Illustrating the importance of Atmospheric deposition as the main Cd source added tosoils in Europe, followed by agrichemicals.

Overall Cd added to soils in Spain if all sludge were soil applied would be very low (0.26g/ha/y in 15 million ha), but considering compost addition with 4 ppm Cd applied at a 5t/ha rate would be near 14 g/ha/y in receiving soils (200,000 ha).

% Sources of heavy metalsMetal Atmospheric deposition Agrichemicals SludgeAs 92 6 2Cd 36-74 10-50 5-12Hg 30 34 6Pb 85-95 11-0.1 4-6Zn 71 10 19

Source: Hansen & Tjell 1979, Hutton&Simon 1986, and 1991.

Source heavy metals added to soils in Europe

Main sources of Cd added to soils in Europe

Additions Sources(g/ha/y)3,5 Fertilizers3,2 (1850-1950) Atmosferic deposition in Great Britain (Rothamsted Agricultural Station)14 (1970-1990)0,26 1 million t sludge 4 ppm applied to 15 million ha14,0 1.4 million t compost 4 ppm Cd applied to a rate of 5 t/haLimit legislation E.U.150 Soil addition limit in 86/278/EEC

Cd increase in soils after biosolids compost application

Soil post-applic. [Cd] ppm: 4 t/ha 8 t/ha20 years 1.10 1.2050 years 1.23 1.46100years 1.45 1.90200years 1.91 2.82

[Cd]= 4 ppm in compost [Cd]= 1 ppm in soil pre-applicationAnnual application 4 t/ha or 8 t/ha Topsoil layer 25 cm, soil density = 1.4 t/m3

149

Cd soil addition limit in 86/278 Directive seems to be very high and non protective forsoils (150 g/ha/y).

If wanting real soil protection against heavy metals contamination in European soils,prevention of atmospheric deposition (mainly due to coal burning) and a globalapproach to all sources seems to be needed.

Cadmium increase in soils after biosolids compost application

Illustrating the low relevance of Cd increase in soils if 4 ppm Cd compost applied atagronomical rates repeatedly for different series of years.

The following does not considering Cd extractions by plants or washing to deeper soillayers and no other sources of Cd added to soils as atmospheric deposition oragrichemicals.

Steps to assure a positive sludge/biosolids agricultural use

Sludge products quality

1. Insure a stable and high physical, chemical, biological sludge products quality(sludge, biosolids, compost, granules, etc).

2. Implement a full Quality Control Program to guarantee sludge products quality.

Soil characteristics3. Previous consideration of soil characteristics, pH and texture (other analysis not

needed) to select type of sludge product applied and design application conditions.

Other environmental conditions4. When designing sludge products application, take into consideration other

environmental conditions: climatic conditions like rain, nearness of groundwateror water courses, topography of the site, etc.

Good practices of sludge products application5. Assure the right use of sludge products through sustainable agricultural practices:

- Guaranteeing the adequate microbiological sludge product quality to the type ofcultivation and harvested part of it.

- Limiting dry matter dose according to a proper fertilization plan that balancesnutrient addition and extractions in soil system.

6. Assure the right use of sludge products through sustainable environmental practices:- Adapting the type of sludge product applied to natural conditions.- Limiting dry matter dose and subsequently total quantity of contaminants and

nutrients added to soil, in order to preserve the balance of nutrients and health ofsoils and preventing groundwater pollution.

150

Information, control and enforcement

7. Need of a system of control and follow up of sludge products generation, treatmentand application realized by an independent third party, with the following purposes:• Information and recordkeeping

- Generation statistics and Quality data• Quality Control

- Survey and checking information on sludge quality.- Survey of sludge tratment facilities and processes.- Follow up of sludge products soil application.

• Enforcement- Developping legal and administrative tools for insure rules compliance and good

practices respect.- Providing human and material resources for real compliance.

Institutional and legislative aspects

8. Environmental public responsibles and institutions must assume their preeminentrole: from information to legislation, from quality and recycling promotion tocontrol and enforcement, paying special attention to administrative competencesdivision and relationships with their agricultural counterparts.

9. Possitive focus on sludge quality and recycling and integrated legislation withother residues, fertilizers and environmental preservation.

10. Implementation of a public acceptance, communication and information systemthat encourages sludge/biosolids recycling policy in the frame of:- Safe and higienic sludge management practices- Sustainable residues management policy- Sustainable materials resources recovery policy- Sustainable agricultural practices model- Suitable environmental conservation model

Conclusions

Weak points

• Pesticides, N, P in water bodies from diffuse sources• Heavy metals added to soils from atmosphere, agrichemicals and organic residuals

(solid waste, sludge, etc)• Organic contaminants to soils (need to evaluate source, quantity, impact and

evolution in soil)• Recyclable industrial sludges non regulated (dairy, paper mill, etc)• Non-recyclable mining sludges, mineral fertilizers industry non regulated (big

quantitities highly polluted).

151

Strong points

• Trend to improved sludge/biosolids quality• Increase in organics demand from agriculture in mediterranean area (also solid

waste compost or biosolids compost)• P, N, Ca, Fe, Mg, S, organic matter in sludges recycled• Need of organics for soil fertility, erosion control in mediterranean area• Increase in composting and stabilization capacity in EU• Dramatics improvements in biosolids compost quality last 10 years.

Proposals

Legislation

• Integrated legislation or at least common standards and certification system fororganics tratment, recycling and application (Urban and industrial sludge products,Solid waste compost, Manures, even mineral fertilizers) from environmental andagricultural perspective.

• Liquid or dewatered sludge direct land application restricted to Water content<72%, Dosis <25 t/ha and high chemical quality.

• Separative collection systems and sewers for domestic and industrial waters (whenindustrial effluents, pretreatment is not enough but separated sewers). Stormwatercontrol and treatment.

• Time progressive quality objectives and simplified self-control procedures inlegislation

Subsidies

• Digestion, Advanced dewatering, Composting, Thermal drying facilities• Action si source (clean sludges come from clean water coming from clean domestic

and industrial sources).

Water and Sludge quality promotion policy

• Clean industries and technologies promotion policies, industrial and domesticeffluents pollutants source control,

• Active sludges stabilization promotion policy: Digestion, Advanced mechanicaldewatering, Composting, Thermal drying,

• High quality sludge products simplified legislative procedures,• Communities and citizens involvement and participation programs.

Bibliography

“Document long term experience of Biosolids Land Application Programs: Final Report” Project 91-ISP- 4. Water Environment Research Foundation. Water Environment Federation, (USA) 1993.

“Effects of biosolids land application in arid and semi-arid environments” U.S.E.P.A. and ColoradoState University (U.S.A.) 1995.

152

“Environmental impact of agricultural practices and agrichemicals” Water Environment Federation,(U.S.A) 1993.

“Fertilizers and Environment International Symposium Proceedings”. Salamanca (Spain). KluwerAcademic Publishers.Amsterdam (Netherlands) 1994.

“Agricultura y Fertilizantes”. Norsk Hydro. Oslo (Noruega) 1990.

“Effect of Heavy Metal pollution on Plants”. Bingham, F.T. Vol. 1, Ed. Leep, N.W. Applied Science.London (U.K.) 1981.

“Composting Source Separated Organics”. BioCycle: Journal of Composting & Recycling. (USA) 1994.

“Long Term Experience of Biosolids Land Application Programs” Water Environment ResearchFoundation (USA ) 1993.

“Aplicación de abonos y enmiendas en una agricultura ecocompatible” Editorial Agrícola españolaS.A. (España) 1992.

“Units Of Expression For Wasterwater Management: Manual practice nº 6” Water EnvironmentFederation (USA) 1982.

“Environemental Impact of Agricultural Practices and Agrichemicals” Yoram Ecktein and AlexanderZaporzec. WEF (USA) 1.994

“Edafología para la agricultura y el medio ambiente” J. Porta. Mundiprensa (España) 1999.

“Efecto del compost de RSU sobre los suelos” Alfredo Polo (CSIC) “Jornadas Técnicas de laAsociación de Ciudades para el Reciclaje”. Jerez de la Frontera (España) 1998.

“Community legislation on Organic Wastes” “Jornadas Técnicas de la Asociación de Ciudades parael Reciclaje”. Jerez de la Frontera (España) 1998.

“Programa de Ensayos agronómicos con lodos de depuración del Instituto Nacional de InvestigadoresAgrarias” CIT INIA, Departamento de Fisiología Vegetal y Tecnología de los Alimentos (España),1990-1998.

“A New Economy for New Century: State of the world 1999” Lester R. Brown & Cristopher Flavin.Worldwatch Institute. Waashington, (USA) 1999.