Journal of Great Lakes Research 36 (2010) 100–112

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Journal of Great Lakes Research

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Temporal and spatial trends of organochlorines and mercury in fishes from theSt. Clair River/Lake St. Clair corridor, Canada

Sarah B. Gewurtz a,b,1, Satyendra P. Bhavsar b,⁎, Donald A. Jackson a,2, Rachael Fletcher b,3, Emily Awad b,4,Rusty Moody c,5, Eric J. Reiner c,6

a Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada M5S 3G5b Environmental Monitoring and Reporting Branch, Ontario Ministry of the Environment, 125 Resources Road, Toronto, Ontario, Canada M9P 3V6c Laboratory Services Branch, Ontario Ministry of the Environment, 125 Resources Road, Toronto, Ontario, Canada M9P 3V6

⁎ Corresponding author. Tel.: +1 416 327 5863.E-mail addresses: Sarah.Gewurtz@ontario.ca (S.B. Ge

Satyendra.Bhavsar@ontario.ca (S.P. Bhavsar), don.jacksoRachael.Fletcher@ontario.ca (R. Fletcher), Emily.Awad@Rusty.Moody@ontario.ca (R. Moody), Eric.Reiner@ontar

1 Tel.: +1 416 327 3171.2 Tel.: +1 416 978 0976.3 Tel.: +1 416 327 2935.4 Tel.: +1 416 327 4989.5 Tel.: +1 416 235 5863.6 Tel.: +1 416 235 5748.

0380-1330/$ – see front matter © 2009 Elsevier B.V. Adoi:10.1016/j.jglr.2009.12.008

a b s t r a c t

a r t i c l e i n f o

Article history:Received 10 April 2009Accepted 8 November 2009

Communicated by Erick R. Christensen

Index words:Sport fishYoung-of-the-year spottail shinerSt. Clair RiverLake St. ClairOrganochlorinesMercury

The temporal and spatial relationships of a suite of organochlorine contaminants and mercury wereexamined in various fish species of the St. Clair River/Lake St. Clair corridor, Canada, in order to evaluate theeffectiveness of remediation efforts and to assess the risk to human and wildlife fish consumers. In Lake St.Clair, fish tissue concentrations of mercury, polychlorinated biphenyls (PCBs), octachlorostyrene (OCS),hexachlorobenzene (HCB), and dichlorodiphenyltrichloroethane (DDT) decreased consistently from the1970s until the 1980s and 1990s, after which the rate of contaminant decline slowed or concentrationsstabilized. This trend was consistent in up to 13 species (both young-of-the-year and adult fishes)comprising different trophic positions and dietary habits, suggesting that the changes were reflective ofambient conditions rather than food web processes. Elevated concentrations of mercury, PCBs, OCS, HCB, andDDT were detected in St. Clair River young-of-the-year spottail shiner compared with fish from Lake Huron,indicating that non-atmospheric inputs of these chemicals, likely originating from sediment, remain in the St.Clair River. Current concentrations of mercury and PCBs, and mercury, PCBs, and DDT remain of concern tohuman and wildlife fish consumers, respectively. Given that contaminant decreases have generally stabilizedin fish, we suggest that further natural recovery of contaminants in St. Clair corridor fishes will be slow sincecontaminants will likely continue to be influenced by sediment levels.

wurtz),n@utoronto.ca (D.A. Jackson),ontario.ca (E. Awad),io.ca (E.J. Reiner).

ll rights reserved.

© 2009 Elsevier B.V. All rights reserved.

Introduction

The St. Clair River/Lake St. Clair system, together with the DetroitRiver, forms the connecting channel between Lake Huron and LakeErie in the Laurentian Great Lakes (Canada and the United States).This system is of great importance due to its use as a shipping channel,drinkingwater for a population of approximately 170,000, cooling andprocess water for industry, recreational activities, and sport andcommercial fisheries (at one time worth more than $1–2 million/year). Contamination in the St. Clair River and Lake St. Clair became ofinterest as early as the 1940s (UGLCCS, 1988). However, public and

government concern increased dramatically following the discoveryof elevated mercury concentrations in fish in 1969 (Fimreite et al.,1971), which led to a commercial fish ban in the 1970s. In 1985, the St.Clair River was identified as an Area of Concern due, in part, tocontaminated fish (St. Clair RAP Team, 2006).

In the 1970s and 1980s, numerous point and non-point sources tothis systemwere identified (King and Sherbin, 1986; Marsalek, 1986).However, industrial sources, especially petroleum refineries andchemical plants located in the upper 10 km of the St. Clair River, bySarnia, Ontario, were found to be mostly responsible for the loadingsof chemicals such as polychlorinated biphenyls (PCBs), hexachlor-obenzene (HCB), octachlorostyrene (OCS), and mercury (King andSherbin, 1986; Marsalek, 1986). Several remediation efforts havetaken place since contamination was first identified as a problem. Forexample, the chlor-alkali plant located in the upper St. Clair Riverclosed in the late 1960s/early 1970, there have been numerousupgrades to industrial and municipal facilities, and sediment has beendredged (target chemicals included mercury and chlorinated organiccompounds) in the upper St. Clair River in 1996 and 2002–2004(Richman and Milani, 2009; St. Clair RAP Team, 2006).

Fish contaminant concentrations provide important informationbecause of the potential risk they pose to humans as consumers of

101S.B. Gewurtz et al. / Journal of Great Lakes Research 36 (2010) 100–112

sport fish. Contaminant trends in fish are often reflective of ambientconditions, although they also depend on changes in the food web,especially in top predatory species (DeVault et al., 1996; French et al.,2006; Paterson et al., 2005). However, with due consideration of foodweb processes, fish concentrations can be used as valuable indicatorsof what is occurring in the ambient environment.

A variety of sport fish species from the St. Clair system have beenmonitored since the1970s for a suite of toxic chemicals by the Sport FishContaminant Monitoring Program (SFCMP) of the Ontario Ministry ofthe Environment (OMOE), in partnership with the Ontario Ministry ofNatural Resources (OMNR) and Health Canada. The OMOE has alsomonitored contaminants in young-of-the-year spottail shiners (Notropishudsonius) in order to assess contamination on a more localized scale.Using data collected as part of these programs, Scheider et al. (1998)found that mercury concentrations in 45 cm walleye (Sander vitreus)from Lake St. Clair decreased between 1970 and 1994, although therewas some indication that concentrations may have been increasingbetween 1990 and 1994. Similarly, Weis (2004) analyzed temporaltrends of mercury in six sport fishes from Lake St. Clair between 1971and 1997. He found that although mercury concentrations generallydecreased over time, the largest decreases occurred in the early 1970s tothe mid-1980s. In the 1990s, concentrations either reached anapproximate asymptotic level or increased. In spottail shiners, concen-trations of PCBs and total-dichlorodiphenyltrichloroethane (total-DDT)decreased at various sites in the St. Clair region between 1978 and 1994(Scheider et al., 1998; Suns et al., 1993).

Although the studies discussed above provide some reporting oftrends in St. Clair River and Lake St. Clair fishes, they have only utilized asmall portion of the OMOE dataset. Furthermore, the previous reportscovered only earlier temporal periods and as various changes tocontaminant inputs and food webs have occurred more recently, thereis aneed to considermore recentdata (through to2007) inorder to assesscurrent conditions of this system and provide an accurate assessment.

Thefirst objective of this studywas to performa comprehensive dataanalysis of temporal and spatial trends in sport and smallfishes in the St.Clair River and Lake St. Clair. Fishes from southern Lake Huronwere alsoassessed for comparative purposes. The second objective was tocompare current concentrations of a suite of different chemicals in fishto consumption guidelines in order to assess whether contaminantconcentrations still pose a risk to human consumers of sport fishes.

Methods

Fish collection

Sport fishes have been collected as part of the on-going SFCMP insouthern Lake Huron, the St. Clair River, and Lake St. Clair since the1970s, primarily by using electrofishing boats. In southern LakeHuron, fishes were collected between Grand Bend (43.302°,−81.761°) and Point Edward, which is the southernmost point ofLake Huron (43.011°, −82.400°) (Fig. 1). In the St. Clair River, fisheswere collected from three locations: the Upper location incorporatedan area from Point Edward to just north of Ethyl Corporation (42.897°,−82.407°), theMiddle locationwas between Ethyl Corporation to justnorth of Lambton Generating Station (42.794°, −82.472°), and theLower location encompassed the area from the Lambton GeneratingStation to the mouth of Lake St. Clair (42.629°, −82.507° W). In LakeSt. Clair, fishes were collected from Mitchell's Bay (42.471°,−82.413°), St. Lukes Bay (42.412°, −82.425°), and Tremblay Creek(42.308°, −82.511°). For southern Lake Huron and Lake St. Clair,spatial variation among specific collection sites was not considered; inLakeHuron, this informationwas not reported and in Lake St. Clair, thisinformation was only reported in 1986, where significant differences(ANOVA, pb0.05) between locations were only present for OCS andHCB in common carp (Cyprinus carpio), mercury in channel catfish(Ictalurus punctatus), and OCS in walleye. However, it should be noted

that the smallfish species (i.e., black crappie (Pomoxis nigromaculatus),pumpkinseed (Lepomis gibbosus), rock bass (Ambloplites rupestris),and yellow perch (Perca flavescens)) have small home ranges andmaynot integrate exposure over these lakes, unlike larger fishes such aswalleye and common carp (Ferguson andDerksen, 1971;Minns, 1995;Stuart and Jones, 2006). In contrast, we considered trends separatelyfor each of the three sampling locations in the St. Clair River. Thisspatial treatment is similar to that in the Guide to Eating Ontario SportFish (OMOE, 2009). Upon collection, the length, weight, and gender ofeach fish were recorded, and a skinless, boneless fillet of the dorsalmuscle was removed and stored frozen at −20 °C until analysis. Allfishes were collected between the late summer to early fall.

Young-of-the-year spottail shiners were collected near-shore at 15sites in southern Lake Huron, the St. Clair River, and Lake St. Clair(Fig. 1), using a 0.6 cm mesh seine. The length of individual fish wasmeasured and the fish were grouped into 10-fish composites based ontheir length. The fish were stored in hexane-rinsed aluminum foil andfrozen at −20 °C until analysis.

Chemical analyses

All chemical analyses were performed at the OMOE, which isaccredited by the Canadian Association for Laboratory Accreditation.Although the chemical analyses were performed over a 30-yearperiod, the methods remained similar, and typically only thedetection limits changed (decreased) because of the use of moresensitive instruments. These analyses have been detailed previously(OMOE, 2006, 2007a,b) and are briefly described below.

Dioxin, furans, and dioxin-like PCBs

Seventeen 2,3,7,8-substituted polychlorinated dibenzo-p-dioxinsand dibenzofurans (PCDD/Fs) and 12 dioxin-like PCBs (dl-PCBs) wereanalyzed using the OMOE method DFPCB-E3418 (OMOE, 2007b).Homogenized samples were fortified with 13C12-labeled surrogatesfor each of the PCDD/Fs and dl-PCBs (Wellington Laboratories,Guelph, ON, Canada). Fish samples (5 g) were digested withhydrochloric acid and extracted with hexane. Sample extracts wereprocessed using a modified silica column, alumina column, and anAmoco PX21 carbon-activated silica column procedure whichresulted in 2 fractions for analysis: Fraction A (mono-ortho-PCBs[PCB 105, 114, 118, 123, 156, 157, 167, 189]), and Fraction B (PCDD/Fsand non-ortho-PCBs [PCB 77, 81, 126, 169]). Analysis was by gaschromatography-high resolution mass spectrometry (GC-HRMS) forfractions A and B separately on a Micromass Autospec HRMS (WatersCorporation, Manchester, UK), tuned to a resolving power of 10,000,coupled to a Hewlett-Packard HP6890 gas chromatograph (AgilentTechnologies, Santa Barbara, CA) equipped with a 40 m DB-5 column(0.18 mm i.d., 0.18 μm film thickness; J&W Scientific, Folsom, CA). Thetwo most abundant ions of the molecular ion cluster were monitoredfor both the native and 13C12-labeled species using selected ionmonitoring (SIM) and results were corrected for surrogate recoveries.Method blanks and matrix spikes were processed with every 10 fieldsamples. Method detection limits (MDL) ranged from 0.3 to 1.2 partsper trillion (ppt) for the tetra to hepta PCDD/Fs, 2 to 3 ppt for the octaPCDD/Fs, and 0.7 to 4.8 ppt for the DL-PCBs.

Percent lipid, total-PCB, and other organochlorines

Total-PCB, OCS, HCB, mirex, photomirex, DDT and metabolites,toxaphene, and chlordane were analyzed using OMOE method E3136(OMOE, 2007a). Fish tissue (5g) was spiked with decachlorobiphenyland 1,3,5-tribromobenzene, digested with hydrochloric acid, andextracted with hexane/dichloromethane. Lipid content was deter-mined gravimetrically. Extracts were then reduced in volume andadded to dry packed Florisil columns. Fraction 1 (20–25 mL hexane)

Fig. 1. Map of the St. Clair River/Lake St. Clair corridor. Black circles show the stations where spottail shiner were collected, where SG=Saugeen River, KC=Kincardine,GD=Goderich, AS=Ausable River, IW=Cape Ipperwash, SA=Sarnia Bay, SC=Suncor, TF=Talfourd Creek, ST=Stag Island, LT=Lambton Generating Station, CO=St. Clair cutoff,MB=Mitchell's Bay, TR=Thames River, PC=Pike Creek, and LR=Little River.

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included PCBs, OCS, HCB, mirex, and photomirex, and Fraction 2 (25%v/v dichloromethane in 20–25 mL hexane) contained DDT (andmetabolites), toxaphene, and chlordane. Both fractions were solventexchanged and reduced to 1 ml iso-octane.

Gas chromatography (GC) with electron capture detection (ECD)was used for analysis of PCBs (HP 6890 GC, Ni63 ECD, MDL=20 ng/gwet weight (ww)), OCS, HCB, mirex, and photomirex (HP 5890 GC,Ni63 ECD, MDL=1, 1, 5, and 4 ng/g ww, respectively), and DDT,toxaphene, and chlordane (HP 6890 Series Plus GC, dual columnmicroNi63 ECD, MDL=2, 50, and 2 ng/g ww, respectively). Calibration

curves were based on six concentrations encompassing the range oftissue concentrations and were accepted if correlation coefficientswere ≥0.985. Total-PCB was quantified using a 4:1 mixture ofAroclors 1254:1260 based on the 23 largest peaks, with a minimumof 11 peaks required for positive identification in samples containinglower amounts of total-PCB. This ratio of Aroclors best resembled thecongener patterns detected for most fish samples. Toxaphene wasquantified using 22 target peaks, which were chosen so that a cross-section of the toxaphene pattern was represented, all peaks could beidentified at the required instrument detection limit, and none of the

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peaks co-elutedwith any of the other compounds analyzed in Fraction2 by this method. Method blanks and matrix spikes were processedwith each set of 20–30 samples. The performance of this method ismonitored through laboratory intercalibration studies (the NorthernContaminants Program (NCP) and Quality Assurance of Informationfor Marine Environmental Monitoring in Europe (QUASIMEME)).

Mercury

Mercurywas analyzed in fishes using OMOEmethodHGBIO-E3057(OMOE, 2006). Fish tissue (0.2–0.4 g) was digested with 4:1concentrated sulfuric to nitric acid (v/v). The digestates were thendiluted with pure water, mixed, and transferred to culture tubes, andplaced in a Gilson autosampler for total mercury determination bycold vapour-flameless atomic absorption spectroscopy (gold-filmJerome Model 511 Hg Analyzer, MDL=0.01 μg/g ww). Calibrationcurves were based on five concentrations encompassing the range oftissue concentrations and were accepted if correlation coefficientswere ≥0.990.

Data analysis

For spatial and temporal trend analysis, we focused on total-PCB,mercury, OCS, HCB, and total-DDT (sum of p,p'-DDT, o,p'-DDT, p,p'-DDD, and p,p-DDE) because, unlike other compounds, data wereconsistently available since the late 1970s/early 1980s throughout thestudy area. Further, point sources of total-PCB, mercury, OCS, and HCBhave been detected in the St. Clair River (King and Sherbin, 1986;Marsalek, 1986) and DDT was a heavily used pesticide in this largelyagricultural area prior to being banned in the United States andCanada in 1972 (Myers et al., 2000; Wong et al., 1995). For allcontaminants, non-detect values were substitutedwith one half of thedetection limit, allowing consistency with previously publishedtemporal trend studies (Bhavsar et al., 2007; DeVault et al., 1996;Huestis et al., 1996; Suns et al., 1993).

In the St. Clair River, we focused on walleye, common carp, andyellow perch as representative sport fishes as these species werecollected and analyzed at multiple time points at all three sections ofthe river. In Lake St. Clair,we further assessed trends in channel catfish,northern pike (Esox lucius), smallmouth bass (Micropterus dolomieui),and white bass (Morone chrysops). Concentrations of mercury wereadditionally evaluated in black crappie, freshwater drum (Aplodinotusgrunniens), largemouth bass (Micropterus salmoides), pumpkinseed,and rock bass due to data availability.

Although concentrations of hydrophobic organic chemicals such asPCBs, OCS, HCB, and DDT partition preferentially into the lipid portionof organisms (Gobas and Morrison, 2000), we opted not to lipidnormalize (i.e., standardize) concentrations because guideline levelsare expressed on a wet weight basis and this better reflects levels towhich humans are exposed. Further, several recent trend studies oforganic contaminants in biota have also expressed data on a wetweight basis (Bhavsar et al., 2007; French et al., 2006; Hickey et al.,2006), which allows consistency with our results. However, becausechanges to lipid content have the potential to influence trend data(Bentzen et al., 1999), we also evaluated trends of PCBs, OCS, HCB, andDDT on a lipid weight basis.

Contaminant concentrations often increase with sport fish length(Miller, 1994; Somers and Jackson, 1993). Themost commonmethodsto account for the influence of fish size are based on linear regression(Scheider et al., 1998; Somers and Jackson, 1993). However, in orderto apply such analysis of covariance methods, there should be asignificant linear relationship between contaminant concentrationand length and the slopes of this regression should not differ amonggroups (Hebert and Keenleyside, 1995; Somers and Jackson, 1993). Inthis study, although in many instances concentrations were lowest inthe smallest sized fish and highest in the largest sized fish, the linear

relationship between the logarithm of concentration and fish lengthwas only consistently significant (ANOVA, pb0.05) for mercury (85%of all species/location/year combinations). In contrast, for total-PCB,OCS, HCB, and total-DDT the logarithm of concentration versus lengthrelationship was significant in less than 30% of the species/location/year combinations. In addition, for most chemical/species/locationcombinations, the slopes of the relationship between the logarithm ofconcentration and length differed (ANCOVA, pb0.05) among years.Therefore we opted to use fish of a limited size range similar to othercontaminant trend studies (Bhavsar et al., 2007; French et al., 2006).

We followed a consistent protocol to select size ranges to includein the analysis. For each chemical/species combination, we firstcalculated the grand mean length across years and locations. We thenselected a size range of 11 cm centered at the mean, to be consistentwith the size range chosen by Bhavsar et al. (2007), and determined ifthere were significant differences (ANOVA, pb0.05) in mean lengthamong years for the selected fish. If there were significant differences,unplannedmultiple comparisons were performed with the Tukey testto identify years showing significant differences. If most pair-wisecomparisons showed no significant differences in length, we kept asize range of 11 cm. Otherwise the size range was narrowed andsignificant differences in length were tested for the narrowed sizerange. Table A1 and Figs. A1–A4 show the length range selected foreach fish species and chemical, as well as the results of the ANOVA andTukey test used to test for significant differences among length in LakeSt. Clair.

In order to evaluate how this method of accounting for fish sizeinfluences the analysis, we also applied the regression-based ANCOVAapproach described by Hebert and Keenleyside (1995) for thespecies/chemicals/locations where chemical concentrations wereconsistently related to length and the slopes of the relationshipbetween the logarithm of concentration and length did not differamong years (ANCOVA, pN0.05) (Fig. A5). In all of these cases, the useof this method did not change the overall trends and there were nosignificant differences between the two lines (ANCOVA, pN0.05),assuming the common exponential decay model as discussed below.

For spottail shiners, there were no significant relationshipsbetween contaminant concentration and length for any chemical/location/year combination. Therefore, we did not incorporate theinfluence of length into our analysis of these fish.

Temporal trendswere evaluated using twomodels. First, we used thecommon first-order exponential decaymodel (Ct=C0 e

k2t), where C0 andCt are the concentrations initially and at time t (year), respectively, and k2is the apparent first-order rate constant, which allows direct comparisonof our results with those who have used a similar model in temporaltrend studies in the Great Lakes (DeVault et al., 1996; French et al., 2006;Huestis et al., 1996; Patersonet al., 2005). Thismodel is intrinsically linearwhen log-transformed and was estimated by ordinary least-squareslinear regression (lnCt=lnC0+ k2t). Second,we used afirst-ordermodelwith a non-zero asymptote (Ct=C0 e

k2t+ Ca), where Ca is the asymptoticor baseline contaminant concentration, and t is the year from the startof the contaminant decrease in the available record (Hickey et al.,2006). The model was estimated using a least-squares loss functionand fitted with the Levenberg–Marquardt Algorithm. Individualconcentration data for each time point were included to incorporatethe variability of each year in our regression analysis, as recommendedby Zar (1984), consistent with several previous studies (Stow et al.,1994; Stow et al., 2004). However, we also performed temporal trendanalysis using arithmetic means (DeVault et al., 1996; French et al.,2006), which led to similar results except that the r2 values weregenerally greater because the use of mean values does not incorporatevariability within years.

The young-of-the-year spottail shiners were used to assess spatialtrends because these fish have small home ranges (b1 km) and thuscan provide more site-specific contaminant information comparedwith sport fishes (Suns and Rees, 1978). Furthermore, they are less

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influenced by spatial differences in food web processes because theyare primarily planktivores and feed on a lower trophic level (Hartmanet al., 1992). Analyses were performed on data from 1999 onwards as

Fig. 2. Temporal trends of mercury (μg/g ww) in fishes from Lake St. Clair. Only fis

this time period is assumed to represent current conditions. For mostchemical/location combinations, there were no significant increasingor decreasing trends from 1999 onwards. Exceptions to this trend (i.e.,

h of a limited size range were included in this figure, as discussed in the text.

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mercury at the St. Clair cutoff and Pike Creek, total-PCB at LambtonGenerating Station and Thames River, OCS at the St. Clair cutoff, andtotal-DDT at Lambton Generating Station, the St. Clair cutoff,Mitchell's Bay, and Thames River) appeared to be due to short-termchanges in concentrations rather than reflective of long-term trends.The assumptions of ANOVA were not met (e.g., the variances weresignificantly heterogeneous (Bartlett's test for homogeneity ofvariances, pb0.05) and the data did not fit normal distributions(Kolmogorov–Smirnov, pb0.05)). Therefore the non-parametricKruskal–Wallis test was used to test for significant differencesamong sites, with unplanned multiple comparisons performed onmean ranks of all pairs of groups (Siegel and Castellan, 1988). Allstatistical analyses were performed using STATISTICA 7.0 (StatSoft,Inc., Tulsa, OK).

Walleye, yellow perch, and common carp were used as represen-tative sport fishes to assess the current state of contamination withrespect to human consumption guidelines. Walleye and yellow perchare the most commonly eaten sport fishes found in the St. Clair River(Dawson, 2000). Although common carp is not commonly eaten, theywere also assessed because they contained elevated concentrations oforganochlorines, due in part to their high lipid content. Further,common carp is the only species where PCDD/Fs and DL-PCBs weremeasured in multiple individuals and locations in the St. Clair River/Lake St. Clair system. The guidelines that we selected are those used toprovide sport fish consumption advice in Ontario, and are derivedfrom health protection guidelines developed by Health Canada(OMOE, 2009). We considered all major chemicals, i.e., mercury,total-PCB, OCS, HCB, total-DDT, mirex, photomirex, toxaphene,chlordane, and PCDD/F and DL-PCB. There were no significant(pN0.05) increasing or decreasing trends from 1999 onwards forany chemical/species/location combination and thus this period wasassumed to represent current conditions. The consumption guidelinevalues for PCDD/Fs and DL-PCBs were based on 2,3,7,8-tetrachlor-odibenzo-p-dioxin toxic equivalent (TEQ) concentrations, whichwerecalculated by summing the multiplication of congener specificconcentrations with their respective 2005 mammalian WorldHealth Organization toxic equivalency factors (TEFs) (Van den Berget al., 2006). All fish sizes were included in the comparison toconsumption guidelines.

Contaminant concentrations in young-of-the-year spottail shiners(data from 1999 onwards) were compared with wildlife protectionguidelines in order to assess whether their contaminant burden posesa risk to their wildlife consumers. The guideline levels that we usedwere the most stringent of three guideline levels: the aquatic lifeguidelines published in the Great LakesWater Quality Agreement (IJC,1994), the Canadian Tissue Residue Guidelines for the Protection ofWildlife Consumers of Aquatic Biota (CCME, 1999), and the fish fleshcriteria for the protection of piscivorous wildlife published by the NewYork State Department of Environmental Conservation (Newell et al.,1987). Chemicals for which guideline levels were available weremercury, total-PCB, OCS, HCB, total-DDT, chlordane, hexachlorocyclo-hexane (HCH; sum of α-, β-, γ-isomers), and mirex.

Results and discussion

Temporal trends

Sport fishesTemporal trends of mercury, total-PCB, OCS, HCB, and total-DDT in

the St. Clair River are shown in Figs. A6–A10, where there was asignificant decrease in concentrations in only 30% of the cases whenthe exponential decaymodel was fit to the data. The application of thefirst-order model with a non-zero asymptote to the St. Clair River dataresulted in non-significant estimations for all parameters, likely due tolack of data.

In order to determine if the lack of consistent temporal trends inthe St. Clair River was an artifact resulting from limited datacollection, we also evaluated temporal trends in Lake St. Clair. Dueto easier fish collection, the dataset for Lake St. Clair is morecomprehensive than that of the St. Clair River. The St. Clair Rivercontributes 98% of the water flow into Lake St. Clair, is a major sourceof pollutants (Gewurtz et al., 2007; Kauss and Hamdy, 1985; Raesideet al., 2009; UGLCCS, 1988), and thus may be representative ofconditions in the St. Clair River.

Mercury concentrations in all fish species from Lake St. Clairdecreased significantly (pb0.05) from the late 1970s until 2007, whenthe common exponential decay model was fit to the data during thisperiod of time (Fig. 2, Fig. A11, and Table A2). However, examinationof plots where mercury concentrations have been log-transformed(Fig. A11) shows that after the mid-1980s, the rate of contaminantdecline appears to have decreased. This result corresponds to whatwas previously found for mercury in yellow perch and common carpin Lake St. Clair and yellow perch from Lake Erie using data collectedup until 1997 (Weis, 2004). Similarly, the exponential decay modelwith non-zero asymptote had significant k2 values for all speciesexcept for freshwater drum (Table A3). The asymptote value wasstatistically significant for all species except common carp andpumpkinseed and exceeded the first level of fish consumptionrestriction for children and women of child-bearing age in Ontario(0.26 μg/g ww) in all other species except for black crappie (TableA3). Given the asymptote represents an irreducible or baselineconcentration and that this temporal trend analysis excluded thelargest and most contaminated individuals, these results indicate thatit will be difficult to reduce mercury levels below this first guidelinelevel if current trends continue.

Scheider et al. (1998) and Weis (2004) found that in Lake St. Clairwalleye and smallmouth bass, mercury concentrations increased from1990 to 1997 (following exponential decreases in the 1970s and1980s). However, when data up until 2007 were included in theanalysis, this increase appeared to be part of a cyclical pattern thatpeaked in the late 1990s (Fig. A11). Such cyclical patterns in fishcontaminant concentrations have been previously detected in otherlakes and species. For example, in Lake Ontario coho and chinooksalmon, upward and downward oscillations in mercury concentra-tions (as well as PCBs, mirex, and DDT) were observed from the early1980s onward and were attributed to the combined influences ofsalmonine stocking and nutrient abatement programs, climatic cycles,and related food web processes (French et al., 2006).

In contrast to walleye and smallmouth bass, mercury concentra-tions in common carp, channel catfish, and black crappie from LakeSt. Clair showed some evidence of increasing trends from the mid-1990s onwards. Monson (2009) found that from the mid-1990s until2006, mercury concentrations generally increased in northern pikeand walleye from Minnesota inland lakes, which may have beenassociated with increasing global emissions and climate change.However, for common carp, channel catfish, and black crappie in LakeSt. Clair, it is difficult to distinguish such possible long-term increasesfrom normal short-term oscillations, with the data available. Inaddition, if such recent increases were reflective of the ambientenvironment, it would likely have been observed in more than 3 of 12species examined.

Similar to mercury, total-PCB, OCS, HCB, and total-DDT decreasedsignificantly (pb0.05) over time when the common exponentialdecay model was fit to the data (Table A2, Figs. 3 and 4, and Figs. A12and A13). Note that the exponential model for HCB was applied todata starting in 1981 due to increases between 1976 and 1981. Theapplication of the exponential model with non-zero asymptoteresulted in non-significant estimations for all parameters likelybecause of the relatively high scatter in the datasets. This scattermay be due to the more complex extraction and cleanup proceduresand the greater proportion of data below the detection limits for the

Fig. 3. Temporal trends of total-polychlorinated biphenyl (PCB, ng/g ww) and octachlorostyrene (OCS, ng/g ww) in fishes from Lake St. Clair. The graph for white bass is not shownbut information for this species is found in Fig. A12. Only fish of a limited size range were included in this figure, as discussed in the text.

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organochlorines compared with mercury. When data were expressedon a lipid weight basis, the overall trends did not change (Figs. A14and A15 and Table A2). Similar to mercury in Lake St. Clair and PCBs inother Great Lake systems (Bhavsar et al., 2007; Hickey et al., 2006),the rate of concentration decline of all four contaminants appears tohave slowed after the early- or mid-1990s (Figs. A12 and A13).

Several hypotheses have been put forward to explain contaminantpatterns in fishes of the Great Lakes. The initial rapid declines from the

beginning of data collection for mercury (1976), total-PCB (1976),OCS (1981), and total-DDT (1976) and from the early-1980s for HCB,until the mid-1980s for mercury and the 1990s for total-PCB, OCS,HCB, and total-DDT were likely in response to control of point sourcecontamination. The chlor-alkali plant located in the upper St. ClairRiver, which was themajor source of mercury to the St. Clair River andLake St. Clair, was decommissioned in the late 1960s/early 1970(UGLCCS, 1988) and the production of both PCBs and DDTwas banned

Fig. 4. Temporal trends of hexachlorobenzene (HCB, ng/g ww) and total-dichlorodiphenyltrichloroethane (DDT, ng/g ww) in fishes from Lake St. Clair. The graph for white bass isnot shown but information for this species is found in Fig. A13. Only fish of a limited size range were included in this figure, as discussed in the text.

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in North America and discharges of PCBs restricted in the Sarnia areain the 1970s (Kauss and Hamdy, 1985; OMOE, 1979; Rapaport andEisenreich, 1988). Although direct discharges of OCS to the St. ClairRiver was only terminated in 1993 (St. Clair RAP Team, 2006), itsphase out from the chlorine industry began in the 1970s (Kaminskyand Hites, 1984). Releases of HCB decreased by 50% between 1988 and2001 in Ontario (Environment Canada, 2000). The apparent slowing

of the rate of decrease or stabilizing of concentrations in the mid-1980s (for mercury) or mid-1990s (total-PCB, OCS, HCB, total-DDT)could be due to a variety of processes. For example, the relativeimportance of contaminated sediment or the atmosphere as sourcesof contamination, which are relatively difficult to control, is likelyincreasing compared with fresh emissions (Gobas et al., 1995). It hasalso been hypothesized that changes to food web processes are

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responsible for the stabilization of concentrations (DeVault et al.,1996). However, the fact that for each chemical, the apparentstabilization occurred in multiple fish species of different trophicpositions having a variety of feeding habits, suggests that thedecreasing rate of contaminant decline is more reflective of ambientconditions compared to changes in food web processes.

Temporal patterns of DDT isomers provide additional informationon changes in sources for this contaminant. Common carp andchannel catfish were used to assess the relative proportion of DDT andmetabolites to total-DDT since these compounds were consistentlydetected above the detection limit and thus calculations were lessinfluenced by non-detect values compared with other species. In bothcommon carp and channel catfish, the proportion of the metabolitep,p'-DDE increased between 1976 and the mid-1980s at the expenseof other isomers (Fig. 5). This metabolite also dominated the isomerdistribution, particularly after 1984, where its contribution to total-DDT ranged from 53 to 86%. This provides further evidence of a switchfrom fresh sources of technical DDT to more weather sources such assediment or the atmosphere. In contrast to fish, the metabolite p,p'-DDD was the dominant isomer in Lake St. Clair surficial sediment,with p,p'-DDE contributing, on average, only 30% to total-DDT(Gewurtz et al., 2007). However, p,p'-DDE is more hydrophobic(log Kow=7.0) and hence more bioaccumulative than p,p'-DDD(log Kow=6.2) (Kwong et al., 2008; Shen and Wania, 2005).

Young-of-the-year spottail shinerFig. 6 shows the temporal trends of mercury, total-PCB, OCS, HCB,

and total-DDT in young-of-the-year spottail shiner at LambtonGenerating Station in the St. Clair River. Temporal trends at fouradditional sites in Lake St. Clair (St. Clair cutoff, Mitchell's Bay, ThamesRiver, and Pike Creek), where fish were consistently collected over

Fig. 5. Dichlorodiphenyltrichloroethane (DDT) isomer patterns (mean±standard errorof the mean) in (a) common carp and (b) channel catfish from Lake St. Clair. Only fish ofa limited size range were included in this figure, as discussed in the text.

Fig. 6. Temporal trends of mercury, total-polychlorinated biphenyl (PCB), octachlor-ostyrene (OCS), hexachlorobenzene (HCB), and total-dichlorodiphenyltrichloroethane(DDT) in spottail shiner at the Lambton Generating Station in the St. Clair River.The p-values are for the fit of the common first-order exponential decay model(lnCt=lnC0+k2t). The p-value denotedwith an asterisk (⁎) indicates a significant increaseover time, whereas all other p-values indicate that concentrations decreased over time.

multiple time points, are shown in Figs. A16–A18. Similar to adultsport fishes, mercury, total-PCB, OCS, and HCB decreased significantly(pb0.05) over time at most locations when the common exponentialdecay model was fit to the data (Table A4). An exception occurred for

Fig. 7. Spatial trends of mercury (μg/g ww), total-polychlorinated biphenyl (PCB,ng/gww), octachlorostyrene (OCS, ng/gww), hexachlorobenzene (HCB, ng/gww), andtotal-dichlorodiphenyltrichloroethane (DDT, ng/g ww) in young-of-the-year spottailshiner at 15 sites in southern Lake Huron, the St. Clair River, and Lake St. Clair. Thedashed and solid lines indicate the detection limits and wildlife protection guidelinelevels, respectively.

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mercury at the Lambton Generating Station, where concentrationsincreased with time; however, concentrations at this site were onlymeasured in fish collected after 1990. The overall trends remained thesame when total-PCB, OCS, HCB, and total-DDT data were expressedon a lipid weight basis (Figs. A19 and A20 and Table A4). Inspection ofplots where contaminant concentrations have been log-transformed(Figs. A16–A18) shows that after around themid-1980s tomid-1990s,the rate of contaminant decline generally slowed. Given that thisslowing is similar to what was observed in sport fishes, it providesfurther evidence that it was more reflective of changes to ambientconditions rather than food web processes.

The exponential decay model with non-zero asymptote was alsofit to mercury data in spottail shiners (the total-PCB, OCS, HCB, andtotal-DDT data resulted in non-significant parameter estimations),where the k2 values were significant only at Mitchell's Bay andThames River (Table A5). The asymptote values of 0.033, 0.030, and0.037 μg/g ww were statistically significant at Mitchell Bay, ThamesRiver, and Pike Creek, respectively. At Pike Creek, the asymptote valuealso exceeded the Canadian Tissue Residue Guideline of 0.033 μg/gww for methylmercury (CCME, 1999) (total mercury consists ofgreater than 95% methylmercury in fish (Bloom, 1992)). It should benoted, however, that this guideline value is within the rangeconsidered “trace” at the OMOE laboratory. The asymptote values atall three locations were well below the International Joint Commis-sion guideline of 0.5 μg/g ww for mercury (IJC, 1994).

Spatial trends

We first evaluated spatial trends of young-of-the-year spottailshiners on a system-wide basis by combining all sites within LakeHuron, the St. Clair River, and Lake St. Clair, respectively. For allchemicals, concentrations in the St. Clair River were significantlyhigher (Kruskal–Wallis, pb0.001) than those from Lake Huron.Mercury, total-PCB, OCS, and HCB concentrations in the St. ClairRiver were also significantly higher (Kruskal–Wallis, pb0.001) than inLake St. Clair; however, there was no significant difference in total-DDT between these two systems. Spatial contaminant trends inshiners at each of the 15 sites evaluated are shown in Fig. 7. Therewere significant differences in chemicals among sites (Tables A6–A10,Kruskal–Wallis, pb0.001), with concentrations at sites in the St. ClairRiver generally greater than concentrations in Lake Huron. The resultswere similar when the data were expressed on a lipid weight basis,except for DDT, where there were less significant differences betweensites (Fig. A21). These results provide evidence that non-atmosphericinputs of these chemicals, likely from previously contaminatedsediment, remain in the St. Clair River. Similarly, Richman and Milani(2009) found elevated concentrations of mercury, OCS, and HCB insediment from the upper St. Clair River compared to upstreamreference sites. Concentrations of mercury and PCBs in suspendedsediment and water were also greater in the lower portions of the St.Clair River compared with upstream reference locations (St. Clair RAPTeam, 2006).

Concentrations of mercury, total-PCB, OCS, and HCB in LakeSt. Clair were not significantly different from Lake Huron on asystem-wide basis (Kruskal–Wallis, pN0.05). In addition, concentra-tions at individual sites in Lake St. Clair were similar to Lake Huron,especially for OCS and HCB (Fig. 7). However, these results were likelyinfluenced by the relatively high frequency of non-detect measure-ments in Lake St. Clair. In addition, because the spottail shiners havenear-shore habitats, fish from Lake St. Clair may be less exposed tocontaminants originating from the St. Clair River, compared withother species. This is because the predominant flow of water, alongwith suspended particles and their associated contaminant burden,moves adjacent to the navigational channel running through thecenter of the lake from the St. Clair River to the Detroit River, andrarely mixes with near-shore water masses (Leach, 1980). Further,

several recent studies using mussels, sediment, and suspendedsediment have found that the St. Clair River is a major source ofpollutants to Lake St. Clair, and in some cases (i.e., mercury, OCS, andHCB) to the Detroit River (Drouillard et al., 2006; Gewurtz et al., 2007;Raeside et al., 2009; Szalinska et al., 2006).

Comparison to guideline levels

For sport fishes, all size ranges were used to assess the currentstate of contamination with respect to human consumption guide-lines, as discussed above. However, fish sampling often targeted the

Fig. 8. Mercury (μg/g ww) and total-polychlorinated biphenyl (PCB, ng/g ww) concentrations versus length in walleye, yellow perch, and common carp in Lake Huron, the St. ClairRiver, and Lake St. Clair in relation to sport fish consumption guidelines. Fish of all sizes from 1999 onwards were included in this figure.

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larger fish and thus the data do not represent a random sample of theSt. Clair fish populations.

Mercury concentrations in yellow perch and carp were generallybelow the first consumption limit guideline of 0.61 μg/g ww for thegeneral population and thus resulted in unrestricted fish consump-tion for all people except for children under 15 and women of child-bearing age (Fig. 8). For walleye, mercury concentrations were, forthe most part, below the first consumption limit guideline for thegeneral population in small fish (b45 cm). However, in larger fish(N60 cm), the first consumption limit guideline for the generalpopulation was exceeded in 82% of individuals and concentrationsapproached the total restriction guideline level for the generalpopulation (1.84 μg/g ww).

PCB concentrations in yellow perch and walleye of all sizes were,for the most part, below the first consumption limit guideline of 105ng/g ww for the sensitive and general populations (Fig. 8). However,PCBs were of more concern in common carp, with the totalrestriction guidelines for the sensitive (211 ng/g ww) and general(844 ng/g ww) populations exceeded in 42 and 16% of mid to large-sized fish (N50 cm), respectively.

Dioxin-like compounds were also of concern in common carpgreater than 50 cm, with 67 and 28% of individuals exceeding thetotal restriction guidelines for the sensitive (5.4 pg/g ww TEQ) andgeneral (21.6 ww TEQ) populations, respectively (Fig. A22). Onaverage, DL-PCBs contributed 69±4.0% (mean±standard error ofthe mean) to total TEQ, suggesting that these exceedances wererelated to a PCB, rather than a PCDD/F, problem.

No other chemical evaluated (i.e., OCS, HCB, total-DDT, mirex,photomirex, toxaphene, and chlordane) exceeded the consumptionlimit guidelines in the fishes evaluated (data are not shown),suggesting that they are no longer of concern to human sport fishconsumers.

The spottail shiners aremore representative of a random sample ofthe St. Clair population since they were all of the same age and theircontaminant burden did not vary with composite fish length. Thewildlife protection guideline for mercury was most often exceeded inthe spottail shiners with 56% of composite samples having concentra-tions greater than 0.033 μg/g ww (Fig. 7). However, as discussedabove, this guideline level is low (within the range considered as“trace” by the OMOE). The mercury concentration in all shinersamples was at least 80% less than the International Joint Commissionmercury guideline of 0.5 μg/g ww (IJC, 1994). The wildlife protectionguideline for total-DDT was also exceeded in a relatively largeproportion of samples (29%) (Fig. 7). The guidelines for total-PCBand OCS were less frequently exceeded in 9% and 1% of the samples,respectively.

No shiner sample exceeded the guideline levels for chlordane,HCB, and HCH. This corresponds to sport fish data and providesfurther evidence that these chemicals are of less concern in theSt. Clair River/Lake St. Clair corridor.

Conclusions

In conclusion, concentrations of mercury, total-PCB, OCS, HCB, andtotal-DDT in sport fishes and young-of-the-year spottail shiner havegenerally decreased since the 1970s in Lake St. Clair. However, therate of concentration decrease has slowed, or in some cases,concentrations have stabilized since the 1980s and 1990s, consistentwith previous reports elsewhere in the Laurentian Great Lakes. Thetemporal trends were generally consistent among multiple sport fishspecies and young-of-the-year spottail shiner, suggesting that thepatterns were reflective of ambient conditions rather than food webprocesses.

No consistent decrease was observed in St. Clair River sport fishes,unlike contaminant trends in Lake St. Clair, even though the former islikely a major source of contaminants to the latter. Furthermore, this

lack of consistent trend does not correspond to patterns observed atother locations throughout the Great Lakes. This inconsistencysuggests that the St. Clair River trends may be an artifact resultingfrom the low frequency of data collection due to difficulty in samplingfish from the river.

Evaluation of spatial trends in spottail shiner showed generallyelevated concentrations of mercury, total-PCB, OCS, HCB, and total-DDT in the St. Clair River compared with Lake Huron. These resultsprovide evidence that non-atmospheric inputs of these chemicals,likely from contaminated sediment (Richman and Milani, 2009),remain in the St. Clair River.

Despite observed contaminant decreases since the 1970s, mercuryand PCBs still pose a risk to human sport fish consumers, particularlythose eating larger sized walleye and carp. Mercury, PCBs, and DDTwere also of concern to wildlife consumers of the young-of-the-yearspottail shiner. Given that the rate of contaminant decline is slowing,our results suggest that natural recovery of contaminant concentra-tions to levels that would no longer be of concern to sport fishconsumers will be slow.

Acknowledgments

We thank Lisa Richman (OMOE) for constructive comments on anearlier version of this manuscript, Steve Petro (OMOE) for construc-tive input and sample collection, and staff of the Laboratory ServicesBranch at the OMOE for chemical analysis.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.jglr.2009.12.008.

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