INTERCOMPARTMENT • RESEARCH ARTICLE

Physicochemical and ecotoxicological evaluation of estuarinewater quality during a dredging operation

Sandro R. Urban & Albertina X. R. Corrêa &

Carlos A. F. Schettini & Paulo R. Schwingel &Rafael M. Sperb & Claudemir M. Radetski

Received: 21 February 2009 /Accepted: 23 October 2009 /Published online: 13 November 2009# Springer-Verlag 2009

AbstractPurpose Most of the information concerning the effects ofcontaminated sediments on estuarine organisms deals withthe impacts of bed forming sediments. The ecotoxicologicalpotential at the time of a dredging operation is moredifficult to assess, and few studies have dealt specificallywith resuspended contaminated sediments. The aim of thisstudy was to determine whether release of contaminantsthrough sediment resuspension during a dredging operationin the Itajaí-açu estuary (Brazil) changed the water qualityclassification and had an ecotoxicological impact on thenear-field water column during the critical moment of thisoperation.Materials and methods Waters from two sites (control anddredged sites) were analyzed for physicochemical parame-ters before, during, and after a dredging operation. Inparallel, a short-term, sensitive battery of biotests (bacteria,algae, and daphnids) was performed with water samplesbefore and during this operation according to the ISObioassay protocols.

Results and discussion No short-term toxicity was ob-served with waters collected before or during the dredgingoperation. The results showed that desorption of contami-nants from suspended particles of sediments with a lowlevel of contamination during a dredging operation loweredthe water quality in the near-field water column but that thisdid not promote significant acute toxicity effects on theorganisms tested.Conclusions More detailed studies are needed (e.g., thequestion of the reliability of biotests under turbulent,particle-rich conditions) to fully understand this complexissue regarding water column ecotoxicity during the wholedredging operation and to support decisions on themanagement of dredging activities.

Keywords Dredging . Ecotoxicology . Environmentalimpact . Estuaries . Metals . PAHs .Water quality

1 Introduction

In coastal areas, estuaries have been recognized as being ofparticular ecological and economic importance (USEPA1999, 2000), but waters and sediments in estuarine areasare subject to multiple anthropogenic or naturally occurringstress factors such as physical, chemical, and microbiolog-ical agents originating from agricultural and urban runoff,municipal sewage, industrial wastewater, and navigationtraffic (Rörig 2005; Darbra et al. 2009; Viers et al. 2009).

In terms of their physicochemical characteristics, estuar-ies are not steady-state systems, which make the spatial andtemporal assessment of their quality an interesting chal-lenge (Förstner 2004). Additional complexity derives fromsediment dredging operations (Gustavson et al. 2008),

Responsible editor: Susanne Heise.

S. R. Urban :A. X. R. Corrêa : C. A. F. Schettini :P. R. Schwingel : R. M. Sperb :C. M. Radetski (*)Centro de Ciências Tecnológicas da Terra e do Mar,Universidade do Vale do Itajaí,Rua Uruguai, 458,Itajaí, Santa Catarina 88302-202, Brazile-mail: radetski@univali.br

Present Address:C. A. F. SchettiniInstituto de Ciências do Mar–LABOMAR,Universidade Federal do Ceará–UFC,Fotaleza, Ceará, Brazil

J Soils Sediments (2010) 10:65–76DOI 10.1007/s11368-009-0156-z

which are necessary to open new harbor terminals or for themaintenance of navigable waterways. This operation causessediment resuspension, which is defined by Hayes andEngler (1986) as sediment particles suspended in the watercolumn during the dredging operation that do not rapidlysettle out of the water column.

According to Collins (1995), regardless of the type ofdredging operation, there are three sediment features thatinfluence the magnitude and distribution of resuspendedsediment in the near-field water column: (a) the physicalcharacter of the sediments being dredged (quantified bygrain size and distribution and specific gravity—relative tothe overlying waters); (b) the condition of the in situsediments as reflected by in situ bulk density, void ratio,and other similar physical measurements; and (c) thephysicochemical characteristics of the sediment or theoverlying waters (e.g., salinity), which might affectthe cohesiveness and consequently the flocculation andsettling of sediment particles. Eggleton and Thomas(2004) present a broad review of the factors affecting therelease and bioavailability of contaminants during sedi-ment disturbance events and recently, a German initiativestarted the Floodsearch project, which aims to combinemethodologies of hydraulic engineering and ecotoxicol-ogy in a new interdisciplinary approach to assess the risksassociated with the remobilization of particulate-boundcontaminants often observed after severe flood events(Wölz et al. 2009).

Although the contaminant contents in sediments are siteand time dependent, generally, metals such as copper, lead,mercury, or zinc and organic compounds such as pesticides,PCBs, and PAHs are the major contaminant constituents(Long 2002). The physical and biological impacts ofdredging operations, which are often related to postdredg-ing activities, are not necessarily directly related to thechemical contamination levels (Wilber and Clarke 2001).Most of the information concerning the effects of contam-inated sediments on estuarine organisms deals with theimpacts of bed forming sediments. The ecotoxicologicalpotential of dredged contaminated sediments is moredifficult to assess and few studies have dealt specificallywith resuspended contaminated sediments (Bonnet et al.2000).

Thus, the purpose of this study was to assess the waterquality and potential ecotoxicological effects of contam-inants resolubilized through sediment resuspension as aresult of a mechanical dredging. To achieve our goals,physicochemical analysis of water was carried out beforeand during a dredging operation. Also, a battery ofbiotests composed of test species belonging to the threetrophic levels of aquatic food chains, i.e., producers(algae), primary consumers (daphnids), and decomposers(bacteria), was performed to assess the ecotoxicological

profile of estuarine waters before and during a dredgingoperation.

2 Material and methods

2.1 Estuary characteristics

The rio Itajaí-açu estuary is located in the south of Brazilat 26.9°S and 48.66°W in the state of Santa Catarina. Theestuary comprises the terminal portion of the rio Itajaí-açu, which drains a basin area of 15,500 km2 encompass-ing 47 municipalities, including a major industrial area insouthern Brazil. The estuary flows over a coastal plain andits morphology resembles a deltaic front estuary accordingto Fairbridge’s physiographic classification (Fairbridge1980). The estuarine width is almost constant, around200 m. The bathymetry ranges from 5 to 9 m with absenceof sand banks, shallows, and tidal flats. The average annualdischarge of the rio Itajaí-açu is 228 m3s−1, with historicalminimum and maximum values of 17 and 5,390 m3s−1,respectively (Schettini 2002). The river discharge is lowmost of the time, under 150 m3s−1, with sparse dischargepeaks produced by rain events in the basin. Significantchanges in the estuarine structure can be observed when thedischarge flow is higher than 500 m3s−1 (Schettini 2002).

The regional tidal regime is microtidal semidiurnal,ranging from 0.4 to 1.2 m during neap and spring tideperiods, respectively (Schettini 2002). The physicalsetting of (a) a small tidal range, (b) a highly variableriver discharge regime, and (c) a deep and uniformchannel morphology results in a highly stratified estuarinestructure (Schettini et al. 2005). A two-layered structureseparated by a halocline is observed most of the time,being stronger during neap tide periods. The salt intrusionduring low discharge periods extends up to 30 km fromthe mouth, and all salt is flushed out when the riverdischarge exceeds around 1,000 m3s−1. The formersituation usually lasts from a few weeks to a couple ofmonths; while the latter usually lasts from a few hours to afew days.

The dredging operation used as the “field laboratory” forthis assessment was performed at nearly 8 km from theestuary mouth, comprising an extension of nearly 250 m ofmargin and 30 m width. Although the volume of dredgedmaterial is relatively small (37,500 m3), it is one of severaldredging operations along the Itajaí-açu estuary. Theoperation lasted for approximately 2 months, and the goalsof the dredging were to increase the water depth near a pierfor ship mooring and to raise the land level on an adjacentland area using the dredged material. The dredger used wasa small hopper dredge with a storage capacity of less than300 m3.

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2.2 Collection, storage, and manipulation of waterand sediments

Three collection events at each of the two sites studied(upper estuary 26°51′56.37″ S 48°41′26.40″ W and dredg-ing zone 26°52′42.86″ S 48°41′25.89″ W) were carried outconsecutively for 3 days, and the grab water sample fromeach event was collected with a Van Dorn bottle (adapted tohigh volume) sampler, while sediments were collected witha small Van Veen grab sampler. The Van Dorn bottle wasattached to the dredger apparatus, which ensure samplingnear the maximum turbidity area during dredging operation.The Itajaí-açu estuary is affected mainly by semidiurnaltides, and samples were taken each day at the low waterphase, at the same time, with similar meteorologicalconditions. The distance between the different collectionpoints was approximately 80 m. The upper estuary site(number 1) was used as the control, and the dredging site(number 2) was the disturbed site. It is important to notethat water was sampled when the turbidity was at themaximal level (during the dredging operation). Water andsediment samples were stored in a refrigerator (−18°C) insealed, completely filled, polyethylene buckets until manip-ulation. To carry out the bioassays, a composite sample(approximately 50:50% mixture) of deeper and superficialwater was filtered (Millipore FG filters, 0.45µm pore size)prior to toxicological testing. All procedures of collection,storage, and manipulation for the toxicological analysiswere based on USEPA methodologies (USEPA 2001).

2.3 Suspended sediments

The distribution of the water column suspended sedimentconcentrations was assessed in situ before, during, and afterthe dredging operation. The probe was lowered into thewater column performing readings at 0.5 m intervals. Anequation to convert the probe readings to suspendedsediment concentrations was obtained through pairs ofprobe readings, and values of suspended sediment concen-tration were determined through analysis of water samples.Water samples (surface and deeper water) were taken toquantify the concentration of suspended sediments by agravimetric method: filtration of a known volume (approx-imately 20 l) through a preweighed filter. The water and(re)suspended solids collected from this filtration providesufficient samples for all parameters investigated (USEPA1998).

2.4 Chemical analysis of water and sediment samples

Water samples were filtered prior to chemical analysis(Millipore FG filters, 0.45µm pore size). For the sedimentanalysis, approximately 30 g of each subsample for PAH

analysis was spiked with the USEPA cocktail of 16standard PAHs as internal standards and homogenized withanhydrous sodium sulfate dried at 150°C for 12 h using amortar and pestle until a free floating powder was obtained.The same procedure was used for the PCB analysis, whereanother sediment subsample was spiked with congenernumbers 28, 52, 101, 118, 138, 153, and 180. Eachhomogenate was shaken with 60 ml carbon disulfide asthe extractor solvent (analytical grade) in a tightly closedbrown glass bottle (250 ml) on a mechanical shakerovernight. The supernatant was decanted, and the extractionwas repeated successively with 2×30 ml carbon disulfide.All fractions were combined and concentrated to approxi-mately 2 ml using rotary evaporation at a pressure of760 mmHg and clean-up with column chromatography. AVarian GC 3400 instrument equipped with a DB-WAXcolumn (60 m×0.25 mm, i.d., 0.25µm film thickness) wasused to perform the analysis according to the USEPAprotocols (USEPA 1996). The injector temperature was280°C (splitless). Chromatographic conditions included aninitial oven temperature of 50°C, with a 2 h 50 min isothermand a program rate of 7°C/min and a final oven temperatureof 240°C with an isotherm of 8 min. The gas carrier was N2,with a column flow of 1 ml min−1, and detection was basedon flame ionization. Six solutions (2, 5, 10, 20, 50, and100 ng ml−1) of the 16 USEPA PAH standards were usedfor the calibration of the equipment. The quantification wasperformed by the external standard method and detectionlimits were 2.0 ng l−1 for water and 0.2 ng g−1dw forsediments, with spiked recoveries of PAHs between 77–113%. All of the samples taken were analyzed in triplicate,and the relative standard deviation was less than 20%.

Determination of chemical and biological oxygen de-mand (COD and BOD), nutrients, and metals, as well ascolimetric analysis were carried out according to astandardized method (APHA et al. 1995).

For metal (and As) determination, approximately 30 g ofeach subsample was extracted in hot acid conditions(HNO3+HF+HCl). For As and Hg, hydride generationand the cold vapor techniques were used, and both elementswere quantified using atomic absorption spectrometry. Theconcentrations of Cd, Pb, Cu, Ni, Zn, and Cr weredetermined using flame or furnace atomic absorptionspectrometry, depending on the metal content. For theanalytical quality control of metals in total sediments, thereagent blank and the international standard referencematerials (US National Institute of Standards and Technol-ogy, SRM 1646a) were tested before analysis, and thedetection lines for the samples were: Cd (0.001), Pb(0.065), Cu (0.030), Cr (0.027), Ni (0.022), and Zn(0.040) in milligrams per kilogram. The mean certifiedvalues for Cd, Pb, Cu, Cr, Ni, and Zn were 0.19, 18.7,10.72, 27.96, 29.6, and 45.0. The mean recovery values

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(with standard deviation in parenthesis) for the referencematerial were 0.15 (0.02) for Cd, 16.1 (1.3) for Pb, 10.01(0.98) for Cu, 22.9 (1.5) for Cr, 27.0 (2.0) for Ni, and 49.0(2.1) for Zn. Water trace metals were determined fromcalibration curves using known standards (CASS-4, Na-tional Research Council of Canada), and the detectionlimits were defined as the concentration value, whichnumerically equals three times the standard deviation often replicate blank measurements as follows: 3µg l−1 forCd, 4µg l−1 for Cu, 5µg l−1 for Zn and Pb, and 20µg l−1 forNi and Cr. All analyses were carried out on replicatesamples, and the coefficient of variation was lower than15%.

2.5 Ecotoxicity tests

2.5.1 Lumistox test

The bacterial (Vibrio fischeri) luminescence inhibition(i.e., Lumistox, Dr. Bruno Lange, Düsseldorf, Germany)test was conducted according to ISO 11384-3 (1996)guidelines at 15±1°C on filtered water samples withsalinity adjustment to 35 parts per thousand at pH7. Theexposure time was 30 min. The lyophilized bacterialreagent was obtained from Deutsche Sammlung vonMikroorganismen und Zellkulturen (DSM number 7151,Braunschweig, Germany). Each of the five sampledilutions (and the control) was performed in triplicate.

2.5.2 Algal growth inhibition test

The algal species used was Skeletonema costatum. Algaltests for each water sample were conducted according toISO 8692 (1989a) guidelines with three replicates perconcentration (or control) of filtered water samples withsalinity adjustment to 31 parts per thousand at pH8.1.Potassium dichromate was used as a positive control. Thecell density of the mixture was adjusted to 10,000 cells permilliliter by dilution with ISO freshwater algal test medium.The test flasks were incubated on a shaker (100 rpm) withcontinuous illumination of 70 mE m−2s−1 (cool-whitefluorescent lamps) at 23±2°C. After 72 h of incubation,the inhibitory effect based on fluorescent activity wasmeasured at 685 nm with a Shimadzu RF-551 (Kyoto,Japan) spectrofluorimeter.

2.5.3 Daphnia magna immobilization test

The 48-h immobilization test with D. magna was per-formed in accordance with the ISO 6341 (1989b) standardat 25±2°C using 20 individuals per replicate (less than 24 hold) in 50 ml glass beakers with 40 ml of test medium.Three replicates per dilution were performed for each water

sample in order to evaluate the variability of the procedure.Each test consisted of five river water dilutions and acontrol group with salinity adjustment to six parts perthousand at pH7.8. Potassium dichromate was used as apositive control.

2.6 Statistics

Statistical analysis was carried out on a microcomputerusing TOXSTAT 3.0 software. Responses were presentedas the mean (X) of assessed endpoints with the coefficientof variation (CV), which was calculated by dividing thestandard deviation by the mean value of the response,multiplied by 100. The William’s test (α≤0.05) was used toobtain the lowest observed effect concentration (LOEC)after applying Shapiro–Wilk’s test for normality andHartley’s test for homogeneity of variance. For daphnids,Fisher’s exact test was used (α≤0.05).

3 Results and discussion

3.1 Suspended sediment distribution

Regarding the objective of this assessment, it is importantto remark that the suspended sediment concentration canvary from tens to thousands of milligrams per liter inresponse to river discharge variations (Schettini andCarvalho 1998). On the other hand, such concentrationvariations are also observed in response to dredgingactivities. Tables 1 and 4 show the results of measuredsuspended particulate matter before and during the dredgingoperation. In terms of time scale, river discharge peaks lastfor hours or days when the suspended sediment concentra-tion can rise to several hundreds of milligrams per liter.Dredging operations usually last for several weeks or acouple of months. In terms of spatial scale, river dischargepeaks affect the entire estuary, while dredging operationeffects are observed locally, in the order of hundreds ofmeters from the dredged site (Schettini and Carvalho 1998).The high variability of river discharges and high levels ofsuspended sediment concentration that follow river dis-charge peaks make it difficult to assess the direct impacts ofdredging and evaluate its deleterious effects on theenvironment.

3.2 Physicochemical and ecotoxicological estuarine aspectsbefore dredging operation

Dredging is a physical operation that changes the physical,chemical, and biological composition of the dredged site.During the dredging operation, an amount of sediment isresuspended in the water column allowing contaminants to

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become partially resolubilized. According to the literaturedata, resolubilization is mainly due to the release of porewater containing dissolved chemicals, desorption fromsediment particles, and loss of particulate-bound contami-nants (Förstner 1987; Förstner and Salomons 2008). Thus,to understand the magnitude of physicochemical changes inthe water quality during a dredging operation, it isnecessary to know the background values of both the waterand sediment at the sites before dredging, which are shownin Tables 1 and 2.

Before dredging, water contaminant levels at site number1 were slightly greater than at site number 2. In general,organic parameters (except oil and grease and nitrite) werehigher in deeper than surface waters at both sites, which canbe explained by sedimentation process that settled thesecontaminants in the estuarine region. High organic contentin surface and deeper waters may originate from diffuseurban untreated sewage and fishing industry wastewaterdischarges. Data for the BOD5/COD mean ratios, rangedfrom 0.31 (site number 1) to 0.36 (site number 2) showingthat natural depuration by aquatic microorganisms could bethe causative agent of dissolved oxygen water depletion(minimum of 4.7 mg l−1 at site number 1 and 3.6 mg l−1 atsite number 2). No Cd, Pb, pesticides, PAHs, or PCBcompounds were detected at the two sites. Metal resolubi-lization from sediments and urban effluent discharges couldbe the reason for the higher concentrations of Cu, Ni, andZn in the deeper waters of site number 2 when compared tothe surface water concentrations at the same site. Moderateor high chemical concentrations of contaminants in watercan cause adverse effects in terms of public health andaquatic biota through direct toxicity and/or bioaccumula-

tion. To avoid these problems, most federal governmentshave established chemical water quality criteria, which areintended to protect aquatic life and human uses of naturalwater bodies. Thus, according to the Brazilian water qualitystandards (CONAMA 2005), water resources are dividedaccording to the preponderant uses into five classes.However, the river analyzed in this study is not classifiedby the state environmental agency, but Table 1 shows thatwater from the Itajaí-açu estuary belongs to class 3 (poorquality) due to the metal (Cu and Zn), organic, andmicrobiological contents. For the metals, the legal limitsfor class 2 are 8µg l−1 for Cu and 0.12 mg l−1 for Zn, whileorganic carbon content must be limited to 5 mg l−1.Coliforms were detected at the two sites examined abovethe limits set by the Brazilian legislation (i.e.,<2.5×103

MPN 100 ml−1).Sediment physicochemical data (see Table 2) showed

that the grain size distribution is predominantly muddy atboth sites. We must emphasize that the three selected pointsin the same site for sample collection have very similarphysicochemical characteristics. Thus, sediment granulo-metric values (%) for site 1 were: clay, 48, 40, and 44; silt,45, 53, and 46; and sand, 7, 7, and 10; and for site 2 were:clay, 50, 48, and 42; silt, 48, 51, and 57; and sand, 2, 1, and1. Organic matter content (%) were: site 1, 2.2, 2.3, and 2.5and for site 2, f1.2, 1.9, and 2.1 while carbonate content(%) were: site 1, 4.7, 5.0, and 5.7 and for site 2, 4.0, 5.1,and 5.2. The values showed in Table 2 for thesecomponents are mean values with CV≤15%. Thus, thisintrasite homogeneity ensures that a small number ofsamples are representative of the entire site, and this canbe verified by the relatively low coefficients of variation

Parameter (unit) Site 1 (Control) Site 2

Surface water Deeper water Surface water Deeper water

SPM (mg l−1) – 299.5 – 530.8

Oil and grease (mg l−1) 1.6–3.4 ND–2.6 2.0–6.6 ND–3.4

COD (mg l−1) 22–61 53–93 38–53 67–94

BOD5 (mg l−1) 6–21 21–38 11–17 26–32

DO (mg l−1) 5.7–7.2 4.7–5.9 4.1–4.6 3.6–4.4

PTotal (%) 0.13–0.15 0.07–0.19 0.02–0.05 0.08–0.16

Nitrate (mg l−1) 3.7–11.2 16.2–19.6 5.8–9.0 12.1–19.8

Nitrite (µg l−1) 49–81 23–50 44–61 20–49

Nkjeldahl (µg l−1) 33–71 17–79 27–66 33–83

Cadmium (mg l−1) ND ND ND ND

Copper (mg l−1) ND ND–0.050 ND ND–0.073

Lead (mg l−1) ND ND ND ND

Nickel (mg l−1) ND ND ND ND–0.05

Zinc (mg l−1) ND ND ND 0.06–0.16

Colimetrya (UFC ml−1) >25,491 >25,491 >25,491 >25,491

Table 1 Physicochemicaland microbiological composi-tion of water at site number1 (control) and site number 2 inthe Itajaí-açu estuary beforedredging

Data shown are lowest andhighest parameter concentra-tions sampled at three differenttimes in three different points ofthe same site (n=9)

SPM suspended particulate mat-ter, COD chemical oxygen de-mand, BOD biochemical oxygendemand, DO dissolved oxygen,PTotal total phosphorus, NKjeldahl

Kjeldahl nitrogen, ND notdetecteda Fecal coliforms

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found in the ecotoxicity assessed endpoints. Overall, sitenumber 1 is less contaminated than site number 2. At theformer site, we found a very low contamination by PAHcompounds and a low level of contamination by metals(and As). Thus, when this sediment contamination iscompared to the Brazilian legislation standards for disposalof sediment after dredging (CONAMA 2004), low levels ofcontamination are indicated (i.e., low probability ofsignificant environmental impact if this sediment is dredgedand disposed of in oceanic waters).

Although the physicochemical analysis provides an insightinto the level of contamination, it is well-recognized that thechemical analysis of total metal concentrations in sedimentgives very little information pertaining to the bioavailableforms of the various inorganic compounds (Tessier et al.1979). According to Calace et al. (2006), metal bioavailabilitycould be considered as a dynamic characteristic, which isvery complex, being dependent on physical, chemical, andbiological factors. On the other hand, biological testsprovided an integrated assessment of sediment quality orwater column effects (Ahlf et al. 2002). Thus, organismresponse was used to integrate the entire suite of potentiallyharmful effects of the water column contaminants accordingto the recommendations of Chapman et al. (1998), whostated that the only accurate way of determining metalbioavailability is to perform bioassays. The short-termtoxicity of contaminants to the aquatic food web (bacteria,algae, and daphnids) was used to assess water qualitybecause these tests are simple, reliable, and relatively

inexpensive. An additional reason to use a battery of biotestsis the different sensitivity of the organisms tested. Sinceestuarine water show salinity variation, two marine and onefreshwater test systems were chosen to assess waterecotoxicity. In this sense, it is more simple and easy toincrease water sample salinity and perform marine tests thaneliminate water sample salinity to perform freshwater test.

Table 3 shows data from the battery of ecotoxicologicaltests carried out with estuarine filtered water samples beforethe dredging operation.

Before the dredging operation, no acute toxicity wasobserved toward the organisms tested, and thus, it is clearthat contaminants present in the suspended sediments werenot released at levels toxic to the tested species.

3.3 Physicochemical and ecotoxicological estuarine aspectsduring dredging operation

When we consider the water quality during the dredgingoperation (Table 4), the parameters measured at site number1 are in the same order of magnitude as those measuredbefore the dredging operation. However, the water qualityof site number 2 changed during the dredging operationleading to water quality deterioration in terms of bothorganic and inorganic components. Thus, according to theBrazilian water quality guidelines, the water quality duringthe dredging operation at site number 2 was classified aspoor (class 3), but the concentrations of metals (Cu and Zn)and As showed an increase at site number 2 during the

Parameter (unit) Site 1 Site 2

Clay/silt/sanda (%) 44/48/8 47/52/1

Organic carbona (%) 2.3 1.7

Carbonatea (%) 5.1 4.8

Nitrogen (%) 0.71–0.73 0.36–0.62

Phosphorus (%) 0.05–0.08 0.05–0.08

Anthracene (µg kg−1) ND–1.3 ND

Benzo(a)fluoranthene (µg kg−1) ND ND–5.6

Benzo(k)phenanthrene (µg kg−1) ND 21.3–27.3

Benzo(a)pyrene (µg kg−1) ND 7.2–12.8

Crisene (µg kg−1) ND 10.3–18.5

Fluoranthene (µg kg−1) ND 18.5–22.7

Naphthalene (µg kg−1) ND ND–1.8

Phenanthrene (µg kg−1) ND ND–4.1

Arsenic (mg kg−1) 3.7–6.3 4.5–6.9

Chromium (mg kg−1) 26.8–32.1 42.0–48.6

Copper (mg kg−1) 25.7–35.2 24.8–40.3

Lead (mg kg−1) 15.7–19.4 21.5–25.7

Mercury (mg kg−1) ND ND

Nickel (mg kg−1) 16.6–28.6 19.6–32.6

Zinc (mg kg−1) 43.6–72.2 63.6–71.2

Table 2 Physicochemical com-position (dry weight basis)of superficial sediments fromthe two sites of the Itajaí-açuestuary before dredging

Data shown are minimum andmaximum parameter concentra-tions for samples collected atthree different times in threedifferent points of the same site(n=9)

ND not detectedaMean values (see text)

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dredging operation. Values of Cu and Zn reached 0.16 and0.36 mg l−1 for which the maximum permissible limits are0.008 and 0.12 mg l−1, respectively, while the Asconcentration reached 0.13 mg l−1 for which the establishedlimit is 0.069 mg l−1. Likewise, the dredging operationincreased the dissolved organic matter in the superficial anddeeper waters (e.g., there was a 2.5-fold increase in themean carbon content). These increases could be attributedto the resolubilization caused by the dredging operation.The effects of dredging on the water contaminant concen-trations was firstly, due to mechanical disturbance of thebed caused by the material suction and secondly, because of

the overflow. Once in the water, the mixture of finesediments and water sinks quickly to the bottom since itsdensity is considerably higher than that of the surroundingwater. Part of the material stays close to the bottom andgradually settles forming the bed. Another part is entrainedinto the surrounding water becoming a true suspension,which will be advected by currents.

In this regard, during dredging operations, resolubiliza-tion of metals and organic compounds from the sediments,even in highly contaminated areas, has been reported to beminimal (Ludwing and Sherrard 1988; EVS 1997). Never-theless, other authors have shown that dredging operations

Table 3 Ecotoxicity results of waters from the control (number 1) and dredged (number 2) sites before dredging of site number 2

Organism test and assessed endpoint Filtered estuarine water (%) Measured endpoint

Site 0.0 6.25 12.5 25.0 50.0 80.0a 100.0 LOEC

Vibrio fischeri luminescence variation Control X 3,224 3,264 3,352 3,184 3,171 3,130 NT >80%CV 9.4 8.4 8.1 8.0 6.0 12.9

Dredged X 3,241 3,142 3,097 3,085 2,971 3,087 NT >80%CV 6.5 11.4 9.6 13.2 10.2 15.3

Skeletonema costatum growth rate Control X 1.068 1.055 1.066 1.044 1.061 1.099 NT >80%CV 10.0 12.8 12.7 11.2 13.4 10.5

Dredged X 0.903 0.913 0.944 1.066 0.964 1.069 NT >80%CV 8.8 11.4 7.3 12.1 12.6 10.8

Daphnia magna lethality Control 0 0 0 0 0 0 0 −Dredged 0 0 0 0 0 0 0 −

Composite sample was collected from the deeper and superficial estuarine water (approximately 50:50% mixture). Data presented are mean of theassessed endpoint and percent coefficient of variation (n=3)

NT not tested, LOEC lowest observed effect concentrationa Highest water proportion tested without color correction for the algal test

Parameter (unit) Site 1 Site 2

Surface water Deeper water Surface water Deeper water

SPM (mg l−1) 184.6 256.9 85,458 109,213

Oil and grease (mg l−1) 5.5–7.5 2.6–3.1 6.1–7.2 3.8–4.0

COD (mg l−1) 22–32 44–55 52–71 109–157

BOD5 (mg l−1) 4–6 12–17 11–20 35–48

DO (mg l−1) 4.6–5.6 4.0–4.6 3.0–3.8 2.5–2.9

PTotal (%) 0.04–0.06 0.03–0.05 0.13–0.15 0.09–0.29

Nitrate (mg l−1) 3.7–5.1 17.5–19.6 7.8–15.4 17.5–26.7

Nitrite (µg l−1) 60–80 20–30 40–61 28–58

Nkjeldahl (µg l−1) 7.9–12.9 7.4–8.2 8.9–11.7 7.1–10.6

Arsenic (mg l−1) ND ND 0.09 0.13

Cadmium (mg l−1) ND ND ND ND

Copper (mg l−1) ND 0.008–0.060 0.01–0.03 0.04–0.16

Lead (mg l−1) ND ND 0.03–0.05 0.04–0.07

Nickel (mg l−1) ND ND ND 0.03–0.07

Zinc (mg l−1) ND 0.06–0.09 0.04–0.09 0.07–0.36

Colimetrya (UFC ml−1) >25,495 >25,495 >25,495 >25,495

Table 4 Physicochemical andmicrobiological composition ofwater at site number 1 (control)and site number 2 (dredged) inthe Itajaí-açu estuary duringdredging of site number 2

Data shown are lowest andhighest parameter concentra-tions sampled at three differenttimes in three different points ofthe same site (n=9)

SPM suspended particulatematter, COD chemical oxygendemand, BOD biochemical oxy-gen demand, DO dissolved ox-ygen, PTotal total phosphorus,NKjeldahl Kjeldahl nitrogen, NDnot detecteda Fecal coliforms

J Soils Sediments (2010) 10:65–76 71

may affect the aquatic biota due to chemical and physicalchanges in the environment (Fredette and French 2004;Cotou et al. 2005; Wilber et al. 2007). The length of timethat sediments are resuspended plays a key role indetermining the chemical impact on the water column(Tomson et al. 2003) and the vast majority of resuspendedsediment settles close to the dredged area within 1 h andonly a small fraction takes longer to resettle (Van Oostrumand Vroege 1994).

To determine whether contaminant release during thedredging operation can cause acute environmental impact,the same battery of toxicity tests was used previously toassess water toxicity, i.e., before the dredging operation.Some physicochemical characteristics of the water at thetime of the collection of samples for use in the battery ofbiotests during the dredging operation are shown in Table 5.

It can be seen in Table 5 that the deeper water has ahigher salinity and lower dissolved oxygen content thanthe surface water, probably, due to the slight salineintrusion and organic matter remobilization resulting fromthe dredging, with its subsequent biodegradation bymicroorganisms.

The results of the ecotoxicity tests during the dredgingoperation are shown in Table 6.

Table 6 shows that neither the EC50 values nor theLOEC was observed when the three test organisms wereexposed to the filtered estuarine water. In natural waters,the resorption and/or complexation of contaminants by clayparticles and organic compounds coming from overflowand the large dilution factor could explain the unavailabilityof contaminants and consequent lack of toxicity response.Thus, it should be noted that metals (and As) in oxicsediments could be scavenged by the iron/manganeseoxyhydroxides and carbonates associated with solid-phasenatural organic matter or bound to the mineral particles insuspension. For the deeper anoxic sediments, the oxy-hydroxides dissolve, releasing the metals, but these in turncould be captured by sulfides formed by the reduction ofsulfate. At the transition zone between oxic and anoxicenvironments in the sediment, conditions may allow theformation and maintenance of sulfide phases. In thistransition zone, if neither oxyhydroxides nor sulfide phasesare present, many metals are solubilized; but there is thepresence of fine clay and/or organic matter from overflow,

Parameter (unit) Site 1 (Control site) Site 2 (Dredging site)

Surface water Deeper water Surface water Deeper water

Air T (°C) 23.7 23.7 23.7 23.7

Water T (°C) 22.0 22.1 22.2 22.2

Salinity (ppt) 2.8 4.1 3.0 5.2

pH 6.92 7.59 7.08 7.48

DO (mg l−1) 3.4 1.5 4.4 1.6

Turbidity (NTU) 62.1 293.6 66.1 776.2

Table 5 Physicochemical com-position of surface and deeperwater samples collected fromthe control and dredging sitesand environmental conditions atthe time of water sampling forecotoxicity tests. Data are meanvalues with CV≤15%

Table 6 Ecotoxicity results of waters from sites number 1 (control) and number 2 (dredged) during dredging operation at site number 2

Organism test and assessed endpoint Filtered estuarine water (%) Measured endpoint

Site 0.0 6.25 12.5 25.0 50.0 80.0a 100.0 LOEC

Vibrio fischeri luminescence variation Control X 3,115 3,068 3,032 3,050 3,061 3,043 NT >80%CV 8.6 7.2 7.9 9.9 10.2 7.5

Dredged X 3,210 2,946 3,111 3,095 3,043 3,033 NT >80%CV 7.8 11.8 12.9 11.7 8.5 10.1

Skeletonema costatum growth rate Control X 0.944 0.914 0.888 0.999 0.936 0.868 NT >80%CV 9.1 7.9 6.9 10.4 8.0 7.5

Dredged X 0.950 0.936 0.898 1.034 1.044 1.054 NT >80%CV 12.8 14.6 11.2 15.1 12.4 17.7

Daphnia magna lethality Control 0 0 0 0 0 0 0 −Dredged 0 0 0 0 0 0 0 −

Composite sample was collected from the deeper and superficial estuarine water (approximately 50:50% mixture). Data presented are mean ofassessed endpoint and percent coefficient of variation (n=3)

NT not tested, LOEC lowest observed effect concentrationa Highest water proportion tested without color correction for the algal test

72 J Soils Sediments (2010) 10:65–76

which could adsorb free contaminants. Thus, only a smallfraction of metal concentrations are resolubilized andbioavailable under normal conditions (EVS 1997; Maddocket al. 2007). For this reason the USEPA (2007) recommendthat assessment of the effects of aqueous metals on aquaticorganisms be based on dissolved metal concentrations.

In relation to metal ecotoxicity based on the literature,48 h LC50 values for D. magna of 93µg Cu l−1 and 7,290µg Ni l−1 have been reported (Khangarot and Ray 1989),and water column concentrations for these metals in adredging zone were found to be between 10.0–160.0µg Cu l−1 and 40.0–70.0µg Ni l−1 (see Table 1). For V.fischeri, 30 min EC50 values of 7.1µg Cu l−1 and 669µg Pb l−1 have been reported (Hsieha et al. 2004), and inour study, water column concentrations for these metals inthe dredging zone were between 10.0 and 160.0µg Cu l−1

and 30.0–70.0µg Pb l−1 (see Table 1). In the case of S.costatum, 72 h EC50 values of 45µg Cu l−1 and 142µg Zn l−1 have been found (Walsh et al. 1988), and in ourstudy, water column concentrations for these metals in thedredging zone were between 10.0 and 160.0µg Cu l−1 and20.0–200.0µg Zn l−1 (see Table 1). Overall, metal watercolumn concentrations could present some toxicity, but itshould be mentioned that toxicity values obtained for ametal solution are quite different from those for complexnatural mixtures. Furthermore, the presence of nutrients inthe water column can promote increases in organismproduction, counter-balancing toxic effects from dissolvedmetals (Rosa et al. 2001). In this regard, our results agree

with other toxicity studies where concentrations of metalsreleased during resuspension of moderately contaminatedsediments were not sufficient to be acutely toxic (Eggletonand Thomas 2004). Although we used short-term ecotox-icity endpoints, our results can be compared with otherexperimental designs carried out to assess the long-termeffects caused by disposal of dredged material in water.Bonnet et al. (2000) used D. magna and Hydra attenuatasurvival to assess the environmental impact of twomoderately contaminated freshwater suspension sedimentsunder flow-through conditions. After 96 h of exposure, theoverlying water of one of the sediment samples showed

Parameter (unit) Site 1 Site 2After dredging After dredging

Organic Carbon (%) 2.0–2.7 1.0–1.9

Carbonate (%) 4.2–5.2 4.2–4.5

Nitrogen (%) 0.68–0.72 0.48–0.56

Phosphorus (%) 0.04–0.06 0.04–0.07

Anthracene (µg kg−1) ND ND

Benzo(a)fluoranthene (µg kg−1) ND ND

Benzo(k)phenanthrene (µg kg−1) ND ND

Benzo(a)pyrene (µg kg−1) ND ND

Crisene (µg kg−1) ND ND

Fluoranthene (µg kg−1) ND ND

Naphthalene (µg kg−1) ND ND

Phenanthrene (µg kg−1) ND ND

Arsenic (mg kg−1) 4.3–5.0 2.7–3.9

Chromium (mg kg−1) 22.2–36.1 15.8–22.2

Copper (mg kg−1) 11.8–28.2 7.8–9.3

Lead (mg kg−1) 12.6–19.5 9.5–11.5

Mercury (mg kg−1) ND ND

Nickel (mg kg−1) 12.2–16.8 6.5–9.5

Zinc (mg kg−1) 63.5–77.2 25.3–48.8

Table 7 Physicochemical com-position (dry weight basis) ofsuperficial sediments from dif-ferent sites of the Itajaí-açuestuary after dredging operation

Data shown are minimum andmaximum parameter concentra-tions for samples collected atthree different times in threedifferent points of the same site(n=9)

ND not detected

Table 8 Metal concentrations in the suspended particles at both,control (site number 1), and dredged (site number 2) sites afterdredging of site number 2

Parameter (unit) Site 1 Site 2

Arsenic (mg kg−1) 5.0±0.6 4.5±0.5

Cadmium (mg kg−1) ND ND

Chromium (mg kg−1) 28.1±1.7 36.6±1.5

Copper (mg kg−1) 26.1±2.0 30.0±1.6

Lead (mg kg−1) 15.1±3.2 13.5±0.9

Nickel (mg kg−1) 17.2±0.9 16.5±0.7

Zinc (mg kg−1) 82.1±3.3 73.1±3.4

The results are the mean values and standard deviation of triplicatesamples

ND not detected

J Soils Sediments (2010) 10:65–76 73

some toxicity toward H. attenuata, which was probably dueto the presence of ammonia and copper, whereas D. magnadid not reveal any toxicity response. This study, therefore,indicates a possible minor impact of dredging on theestuarine water column biota. Thus, the resuspension ofsediments with low level contamination resulted in nonmeasurable toxicity at the dredged site, probably due to themetal speciation since several studies have reported that themetal species were bound to strong binding sites of humiccompounds/black carbon and/or bound to or trapped incolloidal materials (Förstner and Wittmann 1981; Lu et al.1996; Klavins et al. 2000). Nevertheless, it has also beenreported that very high levels of resuspended sediments andturbidity do have the potential to affect aquatic organismsby changing the community composition of benthic macro-invertebrates where thin-layer dredged material was dis-posed of or the sediment was subjected to intense clamdredge-fishing (Wilber et al. 2007; Constantino et al. 2009).However, most of these impacts occur at resuspensionlevels, and durations that are not typically present duringsmall dredging operations or the effects are comparable tothe impact of surface waves on the bottom in wave-dominated environments.

3.4 Physicochemical estuarine aspects after dredgingoperation

Physical removal of contaminated sediment can cause anegative impact on benthic organisms, but for heavilycontaminated sites, we must bear in mind that a dredgingoperation could have positive benefits such as permanentremoval of contaminants from the aquatic system (Voie etal. 2002; Weston et al. 2002). In this regard, when sedimentquality is analyzed after dredging (Table 7), concentrationsof As, Cr, Pb, Ni, and Zn are clearly lower than thoseobserved before the dredging operation (see Table 2).

Data from site number 2 (Table 8) shows that concen-trations of Cu, Pb, Ni, and Zn in the suspended particlesafter the dredging operation are lower than sediment metalconcentrations before the dredging operation, but are in thesame order of magnitude as concentrations found in theestuarine sediments after dredging operation.

Overall, water and sediment concentrations of contam-inants at site number 1 were practically the same before,during, and after the dredging operation, while at sitenumber 2, these concentrations were lower after thedredging operation, with decreases of 31.5% for Zn,43.5% for As, 54.3% for Cr, 55.2% for Pb, 70.8% for Ni,and 76.9% for Cu. As elutriate analysis from particulatematerial in suspension showed the presence of metals afterthe dredging operation, it could be concluded that the lackof water toxicity is due to unavailability of these contam-inants to the aquatic biota.

4 Conclusions

The results of the chemical analysis showed that thesediments from the Itajaí-açu estuary had a low or moderatelevel of contamination. The resuspension events from thedredging operation caused a slight resolubilization ofcontaminants. Although this was sufficient to deterioratethe estuarine water quality, it was not sufficient to causetoxicological impacts when a battery of tests was carriedout with different species of aquatic organisms (bacteria,algae, and daphnids). Thus, the battery of biotests indicatedthat water samples collected from deeper and surface levelsat the critical moment of dredging-resuspension (i.e., whenresolubilization could occur at the maximal level) did notexert a significant acute toxicity effect. Thus, the samplingstrategy applied at the crucial moment of the dredgingoperation together with the battery of ecotoxicological testsimplemented in this study appears to be a useful tool fortoxicity assessment of contaminants released from resus-pended particles of contaminated sediments during dredg-ing operations. Nevertheless, it must be emphasized thatwater samples were collected during the least hydrochemi-cally stable situation of the dredging operation, and thismoment is not a representative of the broader hydrody-namic process that occurs in the estuary during thisoperation. Although the combination of bioassays andchemical analysis could aid the improvement of sedimentand water toxicity criteria, more detailed studies are needed(e.g., the question of the reliability of biotests underturbulent, particle-rich conditions) to fully understand thiscomplex issue regarding water column ecotoxicity duringthe whole dredging operation and to support decisions onthe management of dredging activities.

Acknowledgments The authors greatly acknowledge the fellowshipsupport of CNPq—Brazilian National Council for Scientific andTechnological Development (grants 300898/2007-0 for CM Radetskiand 306217/2007-4 for CAF Schettini).

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