BEHAVIOUR OF HEAVY METALS IN SEWAGE-SLUDGE AMENDED SOIL
Sourav Bhattacharyyaand
Prof. P. K. ManiDEPARTMENT OF AGRICULTURAL CHEMISTRY AND SOIL
SCIENCEFACULTY OF AGRICULTURE
BIDHAN CHANDRA KRISHI VISWAVIDYALAYAMohanpur, Nadia, 741252, India
Essential heavy metal
Non essential heavy metal
Fe, Zn, Cu, Mn, Mo, Ni
Pb, Hg, Cd, Cr, Se
Heavy metals : Atomic no. > 20 Specific gravity > 5
Brady N.C. (2002)
Sewage : Sewage is water-carried waste, in solution or suspension, that is intended to be removed from a community.*
Sludge: A mixture of solid and water, produced during the treatment of waste water or sewage.*
*Central Pollution Control Board(1993)
Table 1. Agricultural use of sewage sludge in different countries:
Country Year Sludge production
(t/yr)
Agriculture(t/yr) % of total
Germany* 2007 2056486 1439540 70
Spain* 2006 1064972 692231 65
Sweden* 2006 210000 30000 14
UK* 2006 1544919 1050544 68
Austria* 2006 252800 38400 16
Italy* 2006 1070080 189554 18
USAa 1998 6900000 2800000 41*United Nations Human Settlement Program (2008)
In India production of sewage sludge is estimated to be around 1000-1300 tonnes/day.
Deshbhratar et al. (2001)
Table 2: The content of heavy metals in agricultural soils (mg/kg)
Country Cr Cu Pb Zn Ni Cd Hg Reference
Spain 63.48 107.65 213.93 427.80 34.75 1.42 -Zimakowska-Gnoinska et al.,2000
America - 95.00 23.00 - 57.00 0.78 - Han et al., 2002
Korea - 2.98 5.25 4.78 - 0.12 0.05 Kim and Kim,1999
Slovakia - 65.00 139.00 140.00 29.00 - - Wilcke, 2005
USA 48.5 48 55 88.5 29 13.5 - Jean-Philippeet al., 2012
India 1.23 2.62 2.82 4.65 0.14 0.05 Prajapati andMeravi, 2014
Iran 10.36 9.62 5.17 11.56 11.28 0.34 -
Sayyed andSayadi, 2011Zojaji et al.,2014
Samples Standards Fe Zn Cu Pb Cd Mn Cr
Water (mg L-1)
Indian Standard (Awashthi, 2000)
NA 5.0 0.05 0.10 0.01 0.1 0.05
WHO/FAO (2007) NA 2.0 0.20 5.0 0.01 0.2 0.10
European Union Standards (EU2002)
- - - - - - -
USEPA (2010) NA 2.00 1.00 .015 .005 .05 0.10Kabata-Pendias(2010) 0.80 NA NA NA NA NA NA
Soil(mg kg-1)
Indian Standard (Awashthi 2000)
NA 300-600 135-270 250-500 3-6 NA NA
WHO/FAO (2007) - - - - - -European Union Standards(EU2002)
NA 300 140 300 3.0 NA 150
USEPA (2010) NA 200 50 300 3.0 80 NAKabata-Pendias (2010) 1000 NA NA NA NA NA NA
Plant(mg kg-1)
Indian Standard (Awashthi, 2000)
NA 50.0 30.0 2.5 1.5 NA NA
WHO/FAO (2007) 450 60.0 40.0 5.0 0.2 500 5.0European Union Standards (EU2002)
NA 60 40 0.30 0.20 NA NA
USEPA (2010) - - - - - - -
Table 3. Guidelines for safe limits of some heavy metals in water, soil & plants
Behaviour of heavy metals in sewage sludge-amended soils and their impact on food composition The concentrations of heavy metals in sludge-amended soils. The bioavailability of these heavy metals to crops. Effects of soil properties on the bioavailability of heavy metals. Changes in bioavailability during the residual period. Differences between crop species and cultivars in the uptake and accumulation of heavy metals in edible organs. Movement of heavy metals in the soil profile and the potential risk of groundwater pollution.
Heavy metal availability in sewage sludge
amended soils
‘Available’ heavy metals - fraction of the total concentration of heavy metals in the soil, which is present in the soil solution or easily exchangeable from the soil exchange surfaces.
Total heavy metal (M)
M in soil solution
Exchangeable
M bound to carbonates
M bound to Fe & Al oxides
M bound to organic matter
Residual fraction
Readily available
Naoum et al. (2001)
=
+
+
+
+
+
Factors affecting heavy metal availability to plant
A)Soil properties
B)Plant factors
C)Soil-plant transfer coefficient
Soil properties
a) pH Availability of cationic
heavy metals decreases with increase in pH
pH
(Alloway and Jackson, 1991)
Whereas, availability of Mo and elements with anionic species increases with increasing soil pH
pH
(Smith, 1996)
b) Organic matter Application of organic matter reduces the mobility of metals in soil and thus lowers their availability to plants.
Environmental Protection Capacity (EPC) factor = DxH2K Dx - thickness of the soil layer (cm) H - soil humus content K - constant depending on the humus quality.
Sludge + O.M Soil humus
EPC Heavy metal availability
Hargitai (1989)
Humic acids bind metals and reduce their availability to plants and thus, metal retention by the soil increases when sewage sludge is applied. Piccolo (1989)
C) Clays and hydrous oxides
Clays and hydrous oxides determine metal availability by -
2) Non-specific adsorption (exchange)
1) Specific adsorption to surface hydroxyl groups (Miller et al., 1987)
3) Co-precipitation (Martinez and McBride, 1998)
4) Precipitation as the discrete metal oxide or hydroxide (Martinez and McBride, 1998).
(Basta and Tabatabai, 1992)
d) Redox potential-
Flooded condition- SO4
2- → SO3 - → S2-
S2- + M2+ → MS
H2S precipitates with Cd in the form of CdS, which is an insoluble compound. Evans (1989)
Metals expected to precipitate as sulphides include Ag+, Ni2+, Zn2+, Hg2+ and Fe3+.
With high P contents, at neutral to alkaline pH, a precipitation of Cd3(PO4)2 takes place.
Increase in the Ca2+ concentration in the solution from 10-3 to 10-2 M, Cd concentration decreases by 67%.
Sulfur, inhibits the transport of Pb in the plants from roots to shoots and it was found that S-deficiency increased Pb movement to the tops.
e) Effects of other elements-
Jing and Logan (1992)
Alloway (1995)
Kabata-Pendias and Pendias(1992)
Antagonistic effect-
f) CaCO3 content-
At high pH and high pCO2 (partial pressure of CO2) values, calcite (CaCO3) sorbs Cd as CdCO3 and diminishes its availability.
Evans (1989)
Other metals likely to precipitate as carbonates at high pCO2 and pH values include: Fe2+, Zn2+ and Pb2+
Evans(1989)
Movement of metals within the profiles of sludged soil
Cd, Cr, Cu, Mo, Ni, Pb and Zn all moved from the surface to within the top 10 cm of the profile, but an average of 87% of metals (range 60-100%)remained in the upper 5 cm after application of sewage-sludge in grassland.
Applications of composted sewage sludge 150 and300 dry t ha-1 on a silt loam soil Zn and Cu concentrations increased down upto 75cm depth with most of the movement occurring in the first year.
In California, found that even after applications of sludges amounting to a maximum of 1800 dry t ha- 1 on a loam soil, Cd, Zn, Ni, and Co tended to remain in the zone of incorporation over a 9 year period.
Williams et al. (1987)
Evans, L.J (1989)
Darmody et al. (1993)
Table 5. Average heavy metal concentration at different depths in a sewage irrigated soil(mg kg-1)
Depth (cm)
Cd Cr Ni Cu Zn Pb As Hg
0-20 0.85 91.21 64.19 41.17 276.41 41.56 17.72 1.72
20-40 0.32 28.18 26.39 8.96 17.25 15.33 15.24 0.83
40-60 0.20 25.29 24.91 7.74 10.26 14.29 6.84 0.21
60-80 0.49 26.08 24.43 7.22 39.60 13.31 2.88 0.09
Wang et al, (2012)
g) Other factors-
Soil moisture
Soil temperature
Soil aeration
Table 5. Total heavy metals content (mg kg−1) in waste water irrigated soils of peri-urban Kolkata(0-20cm)
Parameters Zn Cu Pb Cd Ni
Mean 66.56 27.81 102.9 15.95 36.81
Median 67.42 26.39 106.02 16.72 37.33
Minimum 52.60 13.20 80.08 8.80 19.50
Maximum 84.35 47.40 121.78 18.08 55.40
SD 10.36 10.33 10.22 2.27 9.60
(Saha et al, 2015)
Parameters Unamended soil
6 kg m-2 SSA 9 kg m-2 SSA 12 kg m-2 SSA
pH (1:5) 8.18 8.06 8.09 7.85
EC (mScm-1) 0.24 0.29 0.32 0.39
Organic C (%) 0.77 1.41 1.52 1.74
Total N (%) 0.18 0.20 0.20 0.21
P (mg kg-1) 54.43 111.81 124.2 132.8
Cu (mg kg-1) 3.51 8.50 10.81 11.13
Mn (mg kg-1) 13.27 34.36 41.17 42.05
Zn (mg kg-1) 2.11 11.95 22.95 30.91
Cr (mg kg-1) 0.34 0.77 1.50 1.66
Cd (mg kg-1) 1.51 6.39 6.44 7.36
Ni (mg kg-1) 4.95 9.69 10.29 10.75
Pb (mg kg-1) 2.83 8.49 10.04 11.06
Singh & Agrawal (2010)
Table 6. Effect of sewage sludge on nutrient and heavy metal content in soil
Heavy metal accumulation
in soils and plants
Plant factorsa) Plant speciesMetal High accumulations Low accumulations
Cd Spinach, Lettuce, Celery, Cabbage
Potato, Maize, French bean, Peas
Pb Rye grass, Celery, Kale Some barley cultivars, Potato, Maize
Cu Sugar beet, Certain barley cultivars,
Cabbage, Onion,Leek
Ni Sugar beet, Rye grass, Turnip Maize, Leek, Barley, onion
Zn Spinach, Sugar beet, Beetroot Potato, Leek, Tomato, Onion
McCutcheon & Schnoor (2003)
Table 8. Accumulation of heavy metals (mg kg−1) in crops grown in sewage-irrigated soils
Crops Zn Cu Pb Cd Ni
Sesame (n=10) 24.4 7.9 66.3 13.5 23.8
Chilli (n=6) 32.4 11.2 65.5 11.8 15.4
Okra (n=9) 34.2 9.0 73.3 13.0 19.3
Jute (n=10) 30.7 4.8 68.4 12.7 16.9
Brinjal (n=6) 35.5 6.9 76.4 12.6 23.5
Poi (n=10) 37.5 6.8 79.9 13.1 19.1
Amaranthus (n=4) 33.9 4.8 84.8 13.3 26.6
Colocasia (n=4) 39.3 21.3 91.9 16.8 21.1
Cowpea (n=6) 37.1 4.9 84.1 12.9 21.4
Cauliflower (n=6) 37.3 3.8 70.7 11.6 13.4 All values are mean values Saha et al. (2015)
Other plant factors:b) Cultivars
15 cultivars of potato varied widely in Cd concentrations on the same soil with ranges of 9-39 μgkg-1 on one site and 29-56 μgkg-1 at others.
McLaughlin et al. (1994) c) Genotype
The differences between plant genotypes in term of Cd uptake have also been reported.
Hocking & McLaughlin (2000)
Soil-Plant Transfer Coefficient
Transfer Coefficient (TC)= ----------------[M]plant
[M]soil
[M]plant- concentration of an metal in the test plant tissues
[M]soil- total concentration of the same metal in the soil
where this plant is grown
Table 9. Transfer coefficient (TC) of metals from soil to plants in waste water-irrigated soils of peri-urban Kolkata
Metal Sesame Chilli Okra Brinjal Cauliflower
Zn 0.26–0.70 0.38–0.56 0.28–0.77 0.48–0.65 0.46–0.83
Cu 0.19–0.93 0.15–0.66 0.16–0.69 0.16–0.30 0.07–0.24
Pb 0.44–0.87 0.50–0.77 0.57–1.05 0.59–0.97 0.56–0.71
Cd 0.72–0.94 0.46–0.97 0.52–1.03 0.68–0.83 0.51–0.82
Ni 0.50–1.25 0.22–0.63 0.19–0.93 0.40–0.73 0.22–0.67
Saha et al. (2015)
Effect of sewage sludge amendment on microorganisms activity
A 50% reduction in nitrogen fixation is obesrved in a soil following sewage sludge application. McGrath et al. (1988)
Application of sludge containing low concentration of heavy metals improved soil microbial activities.
Elevated metal concentration have been shown to reduce soil microbial biomass levels, inhibit nitrogen fixation and reduce enzyme activities.
High levels of sludge application (200 t ha–1) significantly reduced the functional diversity of soil community.
Powlson (2002)
Akmal (2005)
Banerjee et al. (1997)
Changes in the availability of heavy metals to crops during the residual period
Any changes which are observed in the bioavailability of metals through time could be due to combinations of several factors-
soil physical properties changes in soil pH Presence of amount of organic matter the reactivity of soil minerals (hydrous oxides of Fe and Mn)
Two types of reversion occurred- Reduction in the formation of soluble ligands due to microbial action. Slow reaction of metals with minerals in solid-solution reactions. Chang et al. (1987)
Changes in the availability of heavy metals to crops during the residual period (contd.)
The metals remained available for uptake, giving anomalously high concentrations of metals in plant organs for many years after application. Chaney et al. (1988)
Availability remained roughly the same.Chang et al. (1982)
Heavy metal concentration decreases after the last sludge application. Hinesly et al. (1979)
McGrath (1987) points out that 9 out of 11 papers showed availability to remain more or less constant over several years.
Changes in the availability of heavy metals to crops during the residual period(contd.)
Table 10. Concentration of heavy metals (mg kg-1) in leaves of Chinese cabbage grown in soil amended with various content of sewage sludge
Heavy metal
Control 5% a 10% a 15% a 20% a 25% a Limits b
As 2.1 5.8 5.9 7.4 10 7.9 0.05
Cd 0.14 0.15 0.25 0.25 0.41 0.24 0.2
Cr 0.7 2.4 3.1 3.2 5.5 5.8 0.5
Pb 0.08 0.17 0.24 0.27 0.19 0.22 9
Ni 1.2 0.6± 1.6 1.6 2.1 3.1 10
Cu 2.6 4.7 5.6±1.1 4.2±0.8 3.6 4.2 20 Zn 43.4 63.3 65.9 78.9 72.5 69.5 100
a Percentages of sewage sludge in soilb Maximum permissible limits of metal contaminants (CEPA)
wang et al. (2008)
Table 11. Concentrations of heavy metals in vegetable edible parts (mg kg-1)
Vegetable Type
Vegetable Species
Pb (mg kg-
1)Cd (mg kg-
1)Cu (mg kg-
1)Zn (mg kg-
1)Root (n=3) Carrot 0.23 0.02 0.22 1.59
Sweet potato 0.61 0.13 0.01 4.67
Solanaceous (n=3)
Brinjal 0.42 0.28 0.93 2.78
Tomato 0.07 0.02 0.46 1.41
Leafy (n=8) Cabbage 0.67 0.03 0.31 9.92
Spinach 0.97 0.51 0.96 20.81
Lettuce 1.16 0.46 0.77 11.79
Legume (n=2)
Asparagrass bean
0.70 0.01 1.99 6.68
Kidney bean 0.03 0.01 1.31 5.66
Zhou et al., 2016
Cumulative accumulation of heavy metals (Cd, Cr, Ni) in edible parts of vegetables (mg kg−1 dry weight) grown in treated sewage water irrigated soils
Ghosh et al., (2011)
Table 12. Yield parameters of mung bean plants grown at different Sewage Sludge amended rates(SSA)
Treatment No. of pods/plant Yield (g m-2) Harvest index (g g-1)
Unamended soil 24.0 102.88 0.346kg m-2 SSA 28.67 143.34 0.409kg m-2 SSA 36.67 180.78 0.4112kg m-2 SSA 33.3 164.50 0.42
Table13 . Heavy metal concentrations in seed of mung bean at different sewage-sludge amendment rates(SSA)Treatment Cu Mn Zn Cr Cd Ni PbUnamended soil
0.48 1.43 11.58 0.32 0.23 0.43 0.42
6kg m-2 SSA 0.77 1.92 20.58 0.83 0.80 1.47 1.889kg m-2 SSA 1.65 2.18 20.62 1.18 1.35 2.85 2.6212kg m-2 SSA 2.22 2.82 22.07 1.47 1.62 5.67 3.47
Singh and Agrawal (2008)
Singh and Agrawal (2008)
Way outs
A) Prevention of heavy metal contamination
B) Management of contaminated soil
Prevention of heavy metal contamination
i) Reducing heavy metal content of sewage sludge-
Acid thermal hydrolysis
Alkaline thermal hydrolysis
Table14. Concentration (mg kg-1 dry solid) of heavy metals in the sludge cake after subjected to hydrolysis
Heavy metals Untreated Acid thermal hydrolysis
Alkaline thermal hydrolysis
Cd 2.05 0.83 2.17Cr 25.5 15.4 14.7Cu 183 189 45Pb 158 148 57Ni 12.7 2.1 13.2Zn 2144 370 1712
Dewil et al. (2006)Order of metal removal from sewage sludge - Acid thermal hydrolysis : Zn = Ni > Cd > Cr >Pb> Cu > Hg Alkali thermal hydrolysis : Cu >Pb> Cr > Zn > Cd = Hg =Ni
Management of contaminated soil
Increasing the soil pH to 6.5 or higher
Draining wet soils
Applying phosphate
Careful selection of plants
Application of organic matter
ConclusionsHeavy metal content of both sewage sludge and soil
should be considered during making decisions regarding sewage sludge use in agriculture.
Risks of heavy metal contamination of crops grown in sewage sludge amended soils can be minimized to some extent by altering various physico-chemical properties of the soil.
Use of sewage sludge should be avoided in crops that accumulate heavy metals in levels toxic to humans without themselves showing any toxicity symptoms.
For safe agricultural use of sewage sludge, regular monitoring of soil and crop edible parts for heavy metal accumulation is necessary.
