distribution of dissolved species and suspended particulate copper in an intertidal ecosystem...

(2006) 203–212www.elsevier.com/locate/marchem

Marine Chemistry 101

Distribution of dissolved species and suspended particulate copper inan intertidal ecosystem affected by copper mine tailings

in Northern Chile

Santiago Andrade a, James Moffett b, Juan A. Correa a,⁎

a Departamento de Ecología and Center for Advanced Studies in Ecology and Biodiversity, Facultad de Ciencias Biológicas,Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile

b Department of Chemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, USA

Received 16 June 2005; received in revised form 10 February 2006; accepted 2 March 2006Available online 17 April 2006

Abstract

The coastline near Chañaral in Northern Chile is one of the most highly Cu-contaminated zones in the world due to dischargesfrom mining activities for more than 60 years. The speciation of Cu has been studied to determine the importance of organiccomplexation in highly contaminated areas, and to assess the likely physiological impacts of Cu on marine organisms. DissolvedCu concentrations of up to 500 nM were measured, completely saturating organic ligands and leading to free Cu2+ concentrationsin excess of 10−8 M. These values are higher than those reported in any other marine environment, and because they occur over anextensive area, provide a unique opportunity to study the effects of Cu on marine ecosystems and to see how Cu behaves when itsspeciation is predominantly inorganic. We found strong gradients in free Cu2+ between Chañaral and adjacent areas with lower Cu,where speciation is dominated by organic complexation. There is also a significant increase in the partitioning of Cu ontosuspended particles in the contaminated areas, consistent with previous studies that showed that organic ligands stabilize Cu in thedissolved phase, whilst “excess” Cu is rapidly scavenged. Those high dissolved Cu concentrations persist in spite of solid phasepartitioning and advective processes along this open-ocean coastline, suggesting that Cu inputs into the system are still very large.Measurements were made using anodic stripping voltammetry with a thin mercury film coated with Nafion, which previousworkers have shown can mitigate ambiguity in the data arising from inadvertent reduction of organic complexes. Our findingssuggest that this is a useful methodology for contaminated systems.© 2006 Elsevier B.V. All rights reserved.

Keywords: ASV; Copper speciation; Particulate copper; Complexing capacity; Mining wastes; Northern Chile

1. Introduction

In most natural waters, Cu speciation is dominated byorganic ligands which significantly lower its biologicalavailability and toxicity, and are also thought to influence

⁎ Corresponding author. Tel.: +56 2 3542620; fax: +56 2 3542621.E-mail address: [email protected] (J.A. Correa).

0304-4203/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.marchem.2006.03.002

the residence time of Cu by influencing its partitioningonto settling particles (Coale and Bruland, 1988; Donat etal., 1994). Organic complexation has a profound effect onthese processes because free Cu2+ concentrations areoften 4–5 orders of magnitude lower than total dissolvedconcentrations (Croot et al., 2000). However, theconcentrations of the strongest ligands are often at ornear the ambient concentration of Cu, so small increasesin Cu can result in large increases in free Cu2+ (Gardner

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http://dx.doi.org/10.1016/j.marchem.2006.03.002

204 S. Andrade et al. / Marine Chemistry 101 (2006) 203–212

and Ravenscroft, 1991). Copper concentrations seldomexceed 50 nM in most coastal waters, even in urbanharbors (Donat et al., 1994;Moffett et al., 1997). Yet thereare several locations in the world where Cu mine wastedisposal has resulted in much higher concentrations overwide areas for prolonged periods of time. These includeEngland (Bryan and Langston, 1992), Canada (Mardsenand DeWreede, 2000; Grout and Levings, 2001; Mardsenet al., 2003), Australia (Stauber et al., 2000) and Chile(Castilla, 1996; Correa et al., 1999; Lancellotti and Stotz,2004). One such site is Chañaral Bay, in Northern Chile,where dissolved Cu concentrations in excess of 1 μMhave been reported in coastal waters (Correa et al., 1999).From Cu titration data in other waters, we anticipated thatmost of the Cu in this system would be inorganicallycomplexed, and would be expected to behave verydifferently than in other environments. However, there arealso reports of biological production of chelators inresponse to Cu stress (Moffett and Brand, 1996; Croot etal., 2000), so it was also possible that free Cu2+ would bemuch lower than predicted from titration data in otherplaces.

We characterized Cu speciation in waters collectedfrom Chañaral in order to distinguish between thesepossibilities, and to determine accurate estimates of freeCu2+ to compliment an ongoing study of Cu effects onmacroalgae and invertebrates in the area. Previous workhad demonstrated significant declines in biologicaldiversity within the site and free Cu2+ estimates are

Fig. 1. Study area and location of the sampling sites (bullets). The current discopen arrow. Dashed lines show the artificial beaches formed by accumulated

required to facilitate comparisons with other studiesand to design quantitative laboratory experiments.Particulate copper was also measured, to determinethe effect of speciation on partitioning and scavengingprocesses.

1.1. Study site

For over 60 years the coastal zone of Chañaral Bay(26° 15′ S; 69° 34′ W), in Northern Chile, has beenimpacted by mining activities from the El Salvador mine(Castilla and Nealler, 1978; Castilla, 1983). The mine is80 km inland, and from 1938 to 1975, ca. 150 milliontons of untreated tailings of the mine were dischargedinto the coast, forming large tailings deposits (Castillaand Nealler, 1978; Castilla, 1983). In 1975, the tailingsdischarge was channeled to a new dumping point atCaleta Palito, 10 km north of Chañaral Bay. From 1976to 1989, a further 130 million tons of untreated minetailings were discharged there, forming a tailings beachat La Lancha, at ca. 6 km north from Caleta Palito. Since1990, only tailings-free wastewater has been dumped atCaleta Palito at a rate of 200–250 l s−1.

Elevated copper concentrations in coastal seawaterhave been accompanied by a decrease in intertidal bio-logical diversity, particularly algal richness (Medina etal., 2005). Although concentrations of dissolved copperhave been measured for this system in the last decade(Correa et al., 1999; Stauber et al., 2005), concentrations

harge point of the copper mine tailing (Caleta Palito) is indicated by antailings.

Table 1Location of sampling stations and parameters recorded in and around Chañaral Bay

Site Code Latitude Longitude T (°C) Salinity pH DO (mmol l−1) SPM (mg l−1)

Caleta Zenteno Z 26°51.082′S 70°48.550′W 15.7±2.2 33.3±1.0 7.97±0.08 0.54±0.01 6.3±1.6Torres del Inca TI 26°36.221′S 70°42.113′W 16.1±1.1 34.2±0.6 8.06±0.06 0.54±0.04 8.9±3.2Caleuche C 26°23.123′S 70°39.949′W 17.1±1.8 33.9±0.9 8.10±0.06 0.53±0.03 7.7±2.3Puerto Chañaral Ch 26°21.117′S 70°38.015′W 17.5±2.3 33.5±0.7 8.08±0.05 0.55±0.03 10.8±3.9Punta Achurra A 26°18.433′S 70°39.834′W 15.9±1.1 33.6±0.6 8.04±0.05 0.56±0.02 7.2±2.8El Faro F 26°18.167′S 70°40.181′W 15.6±0.9 33.8±0.5 8.06±0.14 0.55±0.04 9.4±2.5Palito 1 P 1 26°16.704′S 70°40.001′W 15.8±1.2 33.9±0.4 8.13±0.13 0.53±0.04 14.5±8.5Palito 2 P 2 26°15.798′S 74°40.632′W 16.3±1.0 33.7±0.5 8.01±0.12 0.56±0.06 6.9±1.7La Lancha L 26°13.197′S 70°39.825′W 15.9±2.1 33.5±1.1 8.04±0.06 0.57±0.05 12.9±9.4Pan de Azúcar PAz 26°08.204′S 70°39.248′W 16.4±2.2 33.9±0.6 8.05±0.10 0.54±0.03 10.3±5.6Guanillo G 25°53.774′S 70°41.552′W 16.0±1.5 33.9±0.5 8.00±0.08 0.53±0.03 8.1±2.6Canal Palito (effluent) P 26°18.010S 70°37.743′W 19.3±3.5 66.7±2.2 7.79±0.07 0.49±0.05 42.8±19.1

Mean values±standard deviation of temperature (T), salinity, pH, dissolved oxygen (DO) and suspended particulate matter concentration (SPM).

205S. Andrade et al. / Marine Chemistry 101 (2006) 203–212

and distributions of particulate copper in this intertidalecosystem is unknown.

2. Experimental

2.1. Sample collection

Duplicate seawater samples were collected monthly,fromApril 2003 to January 2004, at eleven localities overa 150-km coastline around Chañaral (Fig. 1). Among thesampling stations (Table 1), Caleta Zenteno (Z), Torres delInca (TI), Pan de Azúcar (PAz) and Guanillo (G), wereconsidered reference sites because they are locatedoutside the reach of the mine tailings. Caleuche (C),Punta Achurra (A) and Puerto Chañaral (Ch) are close tothe old discharge site, where the largest artificial coppertailings beach is currently located. El Faro (F), Palito 1(P1) and Palito 2 (P2), are located within Caleta Palito,where wastes are currently discharged. La Lancha (L) islocated at the north end of Caleta Palito, close to thesecond artificial tailings beach. Samples of the channeledtailings were also included in the study.

Samples were collected near the surface (0.1–0.5 m)with a low density polyethylene (LDPE) bottle securedto a plexiglass holder attached to the end of a 3-m polesampler. Samples were filtered after collection throughacid-washed 0.45 μmMillipore membrane filters, with apolycarbonate filter unit. Samples were stored at 4 °Cuntil analysis.

Membrane filters with retained suspended particulatematter (SPM) were oven-dried at 45±5 °C to constantweight and stored at 4 °C until determinations of coppercontent in the particulate matter.

Temperature, pH, salinity and dissolved oxygen weremeasured in situ using a multisensor device (WTWGmbH, Germany).

2.2. Characterization of copper speciation

Dissolved copper speciation was characterized byanodic stripping voltammetry (ASV) using a Nafioncoated thin mercury film rotating glassy carbon diskelectrode (NCTMF-RGCDE). ASV applied to Cuspeciation in seawater has been described in detailelsewhere (Coale and Bruland, 1988; Scarano et al.,1992; Donat et al., 1994; van Elteren and Woroniecka,2003; Hurst and Bruland, 2005). Seawater is titratedwith copper, and the oxidation current of copperdeposited in the NCTMF-RGCDE is determined as afunction of added copper. During the ASV depositionstep, Cu2+ is reduced to elemental Cu0 at the surface ofthe thin mercury film, forming an amalgam. After thedeposition period, the potential on the mercury electrodeis ramped positive, and the current resulting fromoxidation of the amalgamated copper is measured.

The metal fraction detected by this technique,designated ASV-labile copper (Cu′), is either directlyelectroactive (hydrated Cu2+) or bound to inorganic andorganic complexes (e.g. CuCO3, CuCO3OH

−, CuOH+,Cu–Gly) whose dissociation kinetics, relative to theirresidence times in the electrode diffusion layer are sorapid, that they are kinetically labile and detected aselectro-active species. There are concerns that strongorganic complexes may be reduced and contribute to theCu′ signal, even at relatively modest overpotentials.This confounds attempts to assign a thermodynamicdefinition to Cu′ and may include complexes that are notparticularly bioavailable either. To minimize thisinterference, Hoyer and Jensen (1994) developed aprocedure to coat the thin mercury film with Nafion, asemipermeable coating that significantly impedes thediffusion of some organic complexes to the mercuryfilm. Recently, Hurst and Bruland (2005) have extended


this approach to seawater, and we have adopted theirprotocols here.

Concentrations of labile copper fraction are calcu-lated from:

Cu V¼ ip=S ð1Þ

where Cu′ is the concentration in the labile fraction (i.e.the sum of the concentrations of hydrated Cu2+ and ofinorganically complexed copper), ip is the ASV peakcurrent, S is the sensitivity of the inorganic copperresponse. Sensitivity is given by the slope of the analyticalresponse — signal/metal concentration — during asample titration at copper concentrations exceeding thecopper-complexing organic ligand concentration.

Concentrations of organic copper complexes are calcu-lated from:

CuL ¼ CuT−Cu V ð2Þ

where CuL is the concentration of copper complexedwith natural organic ligand (L), and CuT is the totaldissolved copper concentration. Using these values, theoriginal concentrations of Cu′ and CuL present in thesample can be then calculated.

The titration curve data are linearly transformedaccording to the methods described by Ruzic (1982),van den Berg (1982) and Coale and Bruland (1988),using the Eq. (3), derived from appropriate mass balanceand conditional stability constant relationships:

Cu V=CuL ¼ Cu V=Lþ 1=ðK VCuL;Cu VLÞ ð3Þ

where L is the copper complexing organic ligandconcentration and K′CuL,Cu′ is the conditional stabilityconstant, with respect to Cu′, of the natural coppercomplexes. These two parameters, i.e. conditionalstability constants of naturally occurring organic ligandsand the concentrations of these ligands, determine thecomplexing capacity of the water sample.

2.3. Equipment and instrumentation

Samples were measured at room temperature (25 °C)in a class 100 laminar flow hood, using an Eco ChemieμAutolab 2 connected to an Eco Chemie rotating diskelectrode. The electrode consists of a 60-ml borosilicatesample cup, a rotating glassy-carbon disk workingelectrode (RGCDE) onto which a thin mercury film(TMF) is deposited, a platinum wire counter electrode,

and a Ag/saturated AgCl, saturated KCl reference elec-trode. Samples were deoxygenated with oxygen-freenitrogen.

Total dissolved copper concentration was determinedby ASV after acidified (pHb2) aliquots (15–20 ml)were UV-irradiated by a Metrohm 705 UV digester for90 min.

Concentrations of copper in suspended particulatematter samples were determined by inductively coupledplasma atomic mass spectroscopy in a Perkin ElmerELAN 6100 ICP-MS with an auto sampler AS90,preceded by acid digestion in a microwave MilestoneMLS 1200 Mega.

2.4. Reagents

Thin mercury films were plated onto the RGCDEfrom solutions composed of 50 ml Milli-Q water, 200 μlof 3 M KCl (Merck), and 100 μl of 7000 ppm of Hg2+

solution (Merck). Copper standard solutions wereprepared by dilution of 1000 μg ml−1 atomic absorptionstandard solutions (Baker Analyzed) with Milli-Qwater. A Nafion solution in low weight alcohols(Aldrich) was diluted with methanol to prepare anappropriate solution (5%) and then form the Nafioncoatings. N,N-dimethylacetamide (Aldrich) was used ascasting solvent. Filters with SPM samples were digestedwith suprapur nitric acid (Merck) and hydrogenperoxide p.a. (Merck).

2.5. Dissolved copper determinations

Prior to sample analysis, the RGCDE was po-lished with 0.05 μm alumina at a rotation rate of a fewhundred rpm followed by a thorough rinse with diluteQ-HCl.

Nafion coating of working electrode was achievedby applying 15 μl of Nafion solution and 10 μl ofcasting solvent on the glassy carbon disc. The solventswere dried by heat gun while the electrode was rota-ted at 100 rpm (Hoyer and Jensen, 1994). The thinmercury film was deposited on the Nafion coatedelectrode by immersing it into 50 ml of Milli-Q watercontaining 200 μl of a saturated solution of ultrapureKCl and 100 μl of a 7000 μg ml−1 of Hg2+ solution.The rotation rate of the NCRGCDE was set at5000 rpm, and its potential was kept at −1.2 V withrespect to the Ag/sat. AgCl, sat. KCl reference electrodefor 15 min. The solution was purged with nitrogenduring the processes, when depositing the mercuryfilm. After the deposition period, the TMF-RGCDErotation ceased, and the TMF formation solution was

Fig. 2. Spatial distribution of particulate copper; mean±standard deviation of nine samplings (duplicate) from each site (n=18). Site codes as in Table 1.

Table 2Calculated concentrations of free copper ions in nM

Sites Cu2+

Caleta Zenteno 0.09Torres del Inca 0.10Caleuche 3.04Puerto Chañaral 15.51Punta Achurra 2.45El Faro 2.11Palito 1 4.86Palito 2 5.12La Lancha 17.78Pan de Azucar 0.44Guanillo 0.17


allowed to become quiescent for 30 s. The TMF-RGCDE potential was then ramped positive at 10 mVs− l (50 mV pulse amplitude, 5 pulses s−1) to strip anydeposited metals off the TMF.

The TMF-RGCDE and the cell cup were immersedwith a de-oxygenated aliquot of the sample, and then afresh, deoxygenated sample aliquot (20 ml) was moun-ted into the system. Copper in the sample was depositedinto the TMF-RGCDE for a 3 min deposition step at −0.65 Vand 5000 rpm. Rotation of the NCTMF-RGCDEwas then stopped, the sample allowed to become quie-scent for 5 s, after which the potential was rampedpositive in the square wave model with the oxidationcurrent recorded as described above. The NCTMF-RGCDE potential was kept at −0.15 V for 1 min whilerotating, in order to strip off residual metals from theNCTMF completely.

The sample was spiked with a standard copper solu-tion and the added copper was allowed to equilibratewith the sample for 10 min with the NCTMF-RGCDErotating to enhance mixing, but with no potential ap-plied. After the equilibration, the deposition/ stripping/recording cycle was repeated.

Total dissolved copper in the seawater samples wasdetermined using the methods and procedures describedabove, with slight modifications. 10 ml acidifiedsamples were UV-irradiated for 90 min with a Metrohm705 UV digester neutralized with 0.5 M Q-ammoniasolution, and buffered to pH 8.3. Accuracy was checkedagainst the reference material TMDA 62, provided byThe National Water Research Institute, Canada.

2.6. Copper determinations in suspended particulatematter

Copper in samples of SPM digested with aconcentrated nitric acid (6 ml) and hydrogen peroxide(1 ml) mixture was determined by ICP-MS. Accuracywas checked against high purity reference material(NIST-CRM 1648) provided by the National Institute ofScience and Technology, USA.

2.7. Calculations and data analysis

From the measurements of the Cu oxidation peakheight at each Cu concentration added, a titration plot ofpeak current vs. total Cu concentration was constructedand the concentrations of labile copper (Cu′) and

Fig. 3. ASV-labile copper and Cu complexed with natural ligands, as a fraction of total dissolved copper concentration; and concentration of coppercomplexing ligand. Mean±standard deviation, n=18.

Fig. 4. Representative titration curves of seawater samples obtained byanodic stripping voltammetry, showing oxidation current as a functionof added copper. (A) Torres del Inca, (B) Palito 2 and (C) PuertoChañaral.


organically complexed copper (CuL) were calculated forevery total copper concentration used (Eqs. (1) and (2)).

Free Cu2+ activities were obtained by dividing ASV-labile Cu concentrations by the inorganic side reactioncoefficient for copper (αCu′), been of αCu′=21 for thesalinity and pH of the sample (van den Berg, 1984).

Titration data were linearized by plotting Cu′ /CuLvs. Cu′ (Eq. (3)). Estimates of ligand (L) concentrationsand the conditional stability constant of the corres-ponding copper complexes (K′CuL,Cu′) were obtainedfrom the slope and intercept of the linear least squaresregression of the linearization plot. However, when thetitration curve is straight, we assume there is no excessligand. In this case, total ligand concentration was equalto the total Cu concentration minus the ASV labile Cuconcentration.

The partition coefficient between suspended partic-ulate copper and total dissolved copper (Kd) were cal-culated as follows:

Kd ¼ Cs=Cw ð4Þ

where Kd is in l kg−1, Cs is the copper particulate con-centration (mol kg−1) and Cw is the dissolved copperconcentration (mol l−1).

Significance of the differences in dissolved and parti-culate copper concentrations between sites were as-sessed considering all seawater samples taken duringthe study period using a one-way (between subjects)ANOVA. A post hoc Tukey's multiple comparison test

Table 3Partitioning coefficients (log Kd) calculated for all studied sites,obtained from dividing the average of copper particulate concentration(mol kg−1) by the average value of total dissolved copper (mol l−1)(n=18)

Sites Log Kd

Caleta Zenteno 3.08Torres del Inca 3.63Caleuche 4.47Puerto Chañaral 4.37Punta Achurra 4.67El Faro 4.71Palito 1 4.26Palito 2 4.76La Lancha 4.50Pan de Azucar 3.83Guanillo 3.12


was applied to identify the pairs of sites where signifi-cant differences existed (Zar, 1999).

3. Results

3.1. Environmental parameters

A summary of in situ mean values of temperature,salinity, pH, SPM and dissolved oxygen recordedalong the studied coastline, including those at thechanneled effluent, is shown in Table 1. Concentrationsof SPM were variable among sites, with highest valuesin Palito 1, La Lancha and Puerto Chañaral. In the firstcase (P1) the levels of suspended matter reflect theclose distance from the discharge point, whereas highvalues at La Lancha and Puerto Chañaral seem to be

Fig. 5. Relationship between partitioning coefficients (log Kd) and dissolved c

influenced by the proximity of the artificial tailingbeaches (Fig. 1).

The chemistry of the wastewater in Canal Palito hadvery different properties than the receiving seawater(Table 1). However the effluent does not modify thedistribution of the hydrological parameters determinedin the surrounding seawater.

3.2. Copper in the wastewater of Canal Palito

The average content of copper in the SPM of theeffluent was 9.28 μmol g−1. Mean concentration of totaldissolved copper determined in UV-irradiated wastewa-ter was 0.97 μM. The average concentrations of theASV-labile fraction and complexed fraction were 0.43and 0.45 μM respectively. The mean value of coppercomplexing capacity estimated by ASV measurementsin the samples from the canal was 0.66 μM.

3.3. Copper in coastal seawater

3.3.1. Particulate copperSpatial distribution of copper concentrations indicates

that particulate matter from the sites influenced by thetailings contains levels of the metal that exceed by farthose recorded at the non-impacted sites (Fig. 2).Concentrations varied among sites, ranging from 0.07 to0.48 μmol g−1 dry wt. at the reference sites, and from 4.3to 15.35 μmol g−1 dry wt. in sites affected by the tailings.

3.3.2. Copper speciationMean concentrations of total dissolved copper, ASV-

labile Cu, free Cu2+ and ligand concentration are shown

opper concentrations (total and ASV-labile copper) for all studied sites.


in Table 2 and Fig. 3. Total Cu concentrations span a ten-fold range in concentration, but free Cu2+ concentrationsspan a two hundred-fold range. This difference reflectssaturation of the ligands at the most contaminated sites.Ligand concentration data (Fig. 3) show significanttemporal variability, as the error bars represent thestandard deviation for 9 samples collected over thecourse of the study. However, while there is significanttemporal variability in ligand concentrations within eachsite, there do not appear to be significant differences inligand concentration between sites (F10,22 = 0.66;pN0.5). Thus the principal factor contributing to thelarge range in free Cu is the gradient in total Cu over arelatively uniform background ligand concentration. Ourdata provide no evidence for enhanced production ofligands in the contaminated areas or for any point sourcesassociated with the discharge or tailings.

Representative titration data are shown in Fig. 4. InFig. 4A, samples from a control site show little or noASV-labile Cu at zero added Cu and strong curvaturewith increasing Cu, reflecting a significant concentra-tion of excess ligand. In Fig. 4B, there is a significantlevel of ASV labile Cu in the initial sample, but alsosome excess ligand. In Fig. 4C, there is a very largeamount of ASV-labile Cu and no curvature, indicatingthe ligands are saturated.

3.3.3. Partition between dissolved and particulatefractions

Partition coefficients reported in Table 3 were gene-rally much higher in the contaminated sites relative tocontrol sites. The simplest explanation is that there is acompetition between dissolved and particulate Cubinding sites and Kd is higher in contaminated sitesbecause Cu is less tightly complexed in the dissolvedphase. A log–log plot of ASV-labile Cu versus Kd (Fig.5) reveals a linear relationship with a slope of about 1,consistent with this hypothesis. In contrast, totaldissolved Cu does not correlate with Kd very well(Fig. 5), reflecting the fact that organic complexationinhibits the partitioning. In both cases, however, the dataappear to plateau corresponding to log Kd of 4.5. Aconstant Kd implies that the relative affinity of Cubinding sites in the dissolved and particulate phases isno longer concentration dependent.

4. Discussion

Our results constitute some of the highest estimates offree Cu2+ ever reported in the literature. Strong organicligands, which are ubiquitous buffers of Cu elsewhere,are completely overwhelmed, particularly in those sites

closer to the tailings beaches. While weak organicligands may be influencing Cu in these contaminatedwaters, they must be quite weak to avoid detection andare unlikely to influence our conclusions.

In many contaminated waters around the world, thereare multiple sources of ligands associated with organicmatter in sewage, agricultural runoff, and nutrient-induced eutrophic conditions and, as a consequence,free Cu2+ is still relatively low. In Chañaral bay andsurroundings there are few sources of organic matterexcept for the moderately productive waters associatedwith coastal upwelling (Blanco et al., 2001). This isprobably the most important determinant contributing tothe pronounced ecosystem effects we have encountered.

In the most contaminated sites, more than 50% oftotal Cu is present as ASV-labile Cu. Similar findingswere reported for the copper-mine impacted MacquarieHarbour in Tasmania, Australia, where ASV-labilefraction varied between 50% and 74% of dissolvedcopper (Stauber et al., 2000). Also, in the impacted area,particulate copper represents 25% of the total copperpresent in the medium. These findings suggest that thereare interesting parallels between these systems that meritjoint studies.

Organic ligands are thought to stabilize Cu in solutionby competing with binding sites on settling particles (vanden Berg et al., 1987). Our data support this hypothesis,as Kd increases in samples where the free Cu2+ goes up.This process should lead to a negative feedback controlon Cu concentration as Cu in excess of the ligand israpidly scavenged. However, in the Chañaral systemthere are massive inputs of Cu from Caleta Palito andfrom resuspended contaminated sediments throughoutthe impacted area. The total copper currently dischargedat Caleta Palito was estimated at 550 kg yr−1, based onour data and a flow rate of 0.25 m3 s−1. However, wefound that the highest values of particulate and dissolvedcopper are from Puerto Chañaral and La Lancha, wherehigh Cu originates from re-suspended mine-derivedsediments. Previous studies also concluded that theseunderwater tailings deposits are currently the mainsource of copper (Lee et al., 2002; Lee and Correa, 2005;Ramírez et al., 2005).

Copper in SPM from sites under direct or indirectinfluence of the mine wastes was in agreement withprevious work at Chañaral (Ramírez et al., 2005) andslightly higher than other contaminated sites (Gonzálezand Ramírez, 1995; Achterberg et al., 2003; Ferrer et al.,2003). Particulate copper from the reference sites are inthe same range that those reported as the naturalbackground for coastal and estuarine regions, (González,1991; Waeles et al., 2005), CuT concentrations showed


the same spatial trend as particulate copper and are inagreement with previously data (Lee et al., 2002; Stauberet al., 2005). CuT concentrations at the control sitesremained well below the concentrations recorded at theimpacted area and within the range of historical values(Correa et al., 1999; Lee et al., 2002; Stauber et al.,2005). Nevertheless, they are five to ten-folds higherthan concentrations measured in many other pristinecoastal regions with no previous history of contamina-tion (Moffett et al., 1997; Croot et al., 2000; Batley,1995; Apte and Day, 1998). One possible explanation isthat there may be some residual inputs of Cu to these sitesfrom the Chañaral area, perhaps longshore transport oraeolian deposition. However, in spite of those compar-atively high levels of CuT at the local control sites, noeffect is apparent at the biodiversity level (Medina et al.,2005).

The concentrations of labile copper are in agreementwith previously data from Chañaral measured using thediffusion gel technique, anodic stripping voltammetry,cation exchange resin and copper-sensitive bioassays(Lee and Correa, 2005; Stauber et al., 2005). Coppercomplexing capacity determined for our study area (79–178 nM) is typical for estuaries (Apte et al., 1990;Gardner and Ravenscroft, 1991). While Cu-complexingligand concentrations varied little among the sites, theconditional stability constants (K′) had larger variations.Conditional stability constants were the strongest at thereference sites (i.e. log K′=10.3) and weaker at theimpacted area (log K′=9.2). The weakest copper-binding ligands were detected at sites closer to theartificial tailing beaches of Puerto Chañaral and LaLancha (log K′=6.8). Differences in K reflect the naturaldiversity of ligands in the sample, but also illustrate thedifficulties in comparing titration data compiled at verydifferent Cu concentrations. At the most impacted sites,it is basically impossible to derive binding constant datafor ligands at concentrations well below the ambient Cu.

Chañaral has proven to be a valuable naturallaboratory to study the effects of a single stressor, inthis case Cu, on marine communities (Lee et al., 2002;Stauber et al., 2005). As we seek to apply these findingsto environments with multiple stressors, like urbanharbors, it is important to develop robust, quantitativerelationships between Cu and specific physiologicaleffects. Speciation data presented here are an integralpart of that effort.

Acknowledgements

This study is part of the research program FONDAP1501 0001 funded by CONICYT, to the Center for

Advanced Studies in Ecology and Biodiversity(CASEB) Program 7. Additional support provided bythe International Copper Association to JAC is alsoappreciated. JWM was supported by the Woods HoleOceanographic Institution. We also deeply appreciatethe assistance provided by Sylvain Faugeron, CarolinaCamus and Loretto Contreras during long and exhaus-ting days in the field. Our recognition also goes toMatías Medina, who was a key person in programmingthe field trips, help in the field and advice with statisticalanalyses.

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distribution of dissolved species and suspended particulate copper in an intertidal ecosystem...

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