Mercury concentrations in lentic fish populations related to ecosystem and watershed characteristics

Spatial and temporal variability of mercury in Upper and Lower Red Lake Walleye

Mercury is a global pollutant that is released into our environment by natural and anthropogenic processes resulting in extensive studies of mercury cycling in aquatic ecosystems, and the issuance of human-health-based fish-consumption advisories. We examined total mercury concentrations in Walleye Sander vitreus from Upper and Lower Red Lakes, located in north central Minnesota, between 2019 and 2020. Sampled Walleye (n = 265) ranged from 158 to 610 mm in total length from an age range of young-of-the year to 16 years. Mercury concentrations within the Walleye ranged from 0.030 mg/kg to 0.564 mg/kg (x̄ = 0.179 ± 0.105 mg/kg; x̄ = mean ± sd, all fish-mercury concentrations expressed on wet-weight basis). The best supported model for predicting mercury concentrations in Red Lake Walleye included the independent variables: length, age, sex, and lake basin. This model indicated that there was a significant difference in mercury concentrations between Upper and Lower Red Lake (x̄ = 0.215 ± 0.117 and 0.144 ± 0.077 mg/kg, respectively), and also suggests that individuals who rely on fish for subsistence should target Walleye that are ≤ 400 mm from Lower Red Lake. Observed differences in mercury concentrations could be linked to wetland area influences, fish growth rates, and physicochemical parameters between the two basins. Given that our results illustrated a significant difference in fish-mercury concentrations between basins, future pollutant monitoring efforts should treat Upper and Lower Red Lake as separate lakes and not assume that data from one basin can apply to the other.

Mercury Contamination of an Introduced Generalist Fish of Intermediate Trophic Level

Mercury contamination is a global issue because mercury concentrations in aquatic systems are influenced by both natural and anthropogenic pathways. Here, liver and muscle total mercury (THg) concentrations in black crappie Pomoxis nigromaculatus from three boreal lakes in southeastern Manitoba, Canada, were related to age, morphology and physiological traits to better understand the dynamics of mercury accumulation in an introduced generalist fish species. These THg concentrations were then compared to black crappie mercury concentrations in other Canadian water bodies and to mercury concentrations in other freshwater fishes in southeastern Manitoba. Age and size had strong positive correlations (P < 0.001, r ≥ 0.60) with muscle mercury concentrations. No evidence of acute point source contamination or physiological impairment in black crappie was found in the study area. Analysis of liver THg revealed the possible impacts of seasonal and ontogenetic differences in diet on exposure. Furthermore, THg analysis of liver and muscle tissue showed how generalist foraging may curb the progressively greater mercury exposure and resultant physiological consequences expected from ontogenetic diet shifts in black crappie. Although there appeared to be temporally varied levels of mercury exposure (i.e., liver THg) by sex, there was no sex effect observed in long-term mercury accumulation in the muscle. Black crappie bioaccumulated less mercury at age than primary piscivore species in the region. These results will help foster a better understanding of mercury biomagnification within a region impacted by legacy mercury.

Spatiotemporal changes in largemouth bass mercury concentrations from Connecticut waterbodies, 1995-2021

We evaluated spatiotemporal changes in the mean and variation in largemouth bass (Micropterus salmoides) mercury concentrations over three discrete time periods (1995, 2005-2006, and 2019-2021) across 56 Connecticut waterbodies. We detected largemouth bass raw mercury concentrations that exceeded the US Environmental Protection Agency (USEPA) Fish Tissue Residue Criterion (≥ 0.30 µg g^-1 ww) in 75.1%, 63.3%, and 47.7% of all fish sampled during 1995, 2005-2006, and 2019-2021, respectively. Total length (TL)-adjusted largemouth bass mercury concentrations declined across all ecoregions in Connecticut between subsequent sampling periods but increased between 2005-2006 and 2019-2021 in the Northwest Hills/Uplands ecoregion. The coefficient of variation (CV) of largemouth bass TL-adjusted mercury concentrations increased through time, increasing from 25.78% during 1995 to 36.47% during 2019-2021. The probability of a largemouth bass having a raw mercury concentration > 0.30 µg g^-1 ww increased with total length (TL), but the TL with a 50% probability varied across ecoregions and periods. The variation in largemouth bass mercury concentrations highlights the roles that changes to individual behaviors, food web structure, lake properties, and legacy mercury may play in shaping broad patterns and trends in mercury consumption risks.

Factors related to fish mercury concentrations in Iowa lakes

Mercury contamination in aquatic ecosystems is a global concern due to the health risks of consuming contaminated fishes. Fish mercury concentrations are influenced by a range of biotic and abiotic factors that vary among regions, but these complex interactions are difficult to disentangle. We collected bluegill (Lepomis macrochirus), white and black crappie (Pomoxis annularis; P. nigromaculatus), largemouth bass (Micropterus salmoides), walleye (Sander vitreus), muskellunge (Esox masquinongy), and northern pike (E. lucius) from waterbodies throughout Iowa and analyzed them for mercury concentrations. We used land use, water chemistry, and fish characteristics to explain variation in mercury concentrations among and within systems. Mercury concentrations were generally low and undetectable (< 0.05 mg/kg) in 43% of fish analyzed. Detected mercury concentrations were highest in largemouth bass, muskellunge, northern pike, and walleye, lowest in black and white crappie and bluegill, and positively related to fish length and age. Mean lake depth, pH, watershed area to lake area ratio, and percent of watershed as open water were positively related to fish mercury concentrations whereas lake area and percent of watershed as agriculture, developed, forested, and grassland were negatively related to mercury concentrations. Additionally, mercury concentrations were higher in shallow natural lakes compared to other lake types. Our results indicate fish mercury concentrations are lower in Iowa lakes compared to other regions. Models we developed in this study can be used to identify other waterbodies that may have elevated mercury concentrations that can guide fish mercury monitoring programs.

Downstream Modification of Mercury in Diverse River Systems Underscores the Role of Local Conditions in Fish Bioaccumulation

Fish consumption advisories for mercury (Hg) are common in rivers, highlighting connections between landscape sources of Hg and downstream fluvial ecosystems. Though watershed conditions can influence concentrations of Hg in smaller streams, how Hg changes downstream through larger rivers and how these changes associate with Hg concentrations in fish is not well understood. Here we present a continuum of concentrations and yields of total mercury (THg) and methylmercury (MeHg) from small tributary systems draining diverse western Canadian headwater landscapes through to major transboundary rivers. We associate these downstream patterns with THg concentrations in tissues of resident fish in major rivers. Mean concentrations and yields of unfiltered THg from over 80 monitored tributaries and major rivers were highly variable in space ranging from 0.28 to 120 ng L−1 and 0.39 to 170 µg ha−1 d−1, respectively. Using spatial data and a hierarchical cluster analysis, we identified three broad categories of tributary catchment conditions. Linear mixed modeling analysis with water quality variables revealed significantly lower THg concentrations in tributaries draining cordillera-foothills (geometric mean: 0.76 ng L−1) regions relative to those draining forested (1.5 ng L−1) and agriculturalized landscapes (2.4 ng L−1), suggesting that sources and mobility of THg in soils and surface waters were different between landscapes. However, these concentration differences were not sustained downstream in major rivers as local sources and sinks of THg in river channels smoothed differences between landscape types. Extensive fish tissue monitoring in major rivers and ANCOVA analysis found that site-specific, river water THg and MeHg concentrations and local catchment conditions were stronger associates of THg concentrations in fish than broader trends in rivers within and across landscape classes. Consequently, site-specific, targeted monitoring of THg and MeHg concentrations in water and fish is a preferred study design when assessing regional-level patterns in fish tissue concentrations.

Use of occupancy modelling to identify sample sizes and waterbodies with fish exceeding mercury consumption advisory thresholds

Identifying waterbodies where fish methylmercury concentrations are elevated is critical for development of consumption guidelines. However, mercury concentrations vary among waterbodies and fishes due to a suite of environmental conditions and detection of elevated mercury concentrations is imperfect, resulting in inaccurate consumption guidelines. Occupancy models may be a useful approach for addressing these issues but have not been used for these purposes. Our objectives were to use occupancy modeling to (1) estimate number of samples needed to detect mercury levels surpassing >0.30 mg/kg wet weight in fish at a waterbody (2) identify individual fish-level factors associated with detection probability, and (3) identify environmental-level factors linked to elevated mercury levels in fish at a waterbody. Mercury concentrations were estimated from >500 largemouth bass Micropterus salmoides and walleye Sander vitreus from 30 waterbodies throughout Iowa, USA to identify individuals with concentrations > or <0.30 mg/kg. Probability of detecting mercury concentrations >0.30 mg/kg varied between species and increased with fish length; consequently, more samples were needed to detect elevated mercury concentrations in small versus large fish. The probability of a waterbody having fish with elevated mercury levels increased with the percent grassland and declined with percent agriculture in the watershed, providing prioritization metrics for mercury surveillance programs. Our results demonstrate that occupancy models can be a valuable tool for mercury surveillance due to their ability to estimate necessary sample sizes and identify fish sizes and waterbodies with elevated mercury concentrations while accounting for imperfect detection probabilities.

Effects of Non-native Fish on Lacustrine Food Web Structure and Mercury Biomagnification along a Dissolved Organic Carbon Gradient

Although the introduction of non-native fish species has been shown to alter trophic ecology in aquatic ecosystems, there has been limited research on how invasive species alter methylmercury (MeHg) biomagnification in lacustrine food webs. We sampled surface water and biota from 8 lakes in Quebec, Canada, spanning a range of dissolved organic carbon (DOC) concentrations (2.9-8.4 mg/L); 4 lakes were inhabited by native brook trout (Salvelinus fontinalis), and the remaining lakes contained brook trout and a non-native fish, Allegheny pearl dace (Margariscus margarita). Periphyton, zooplankton, macroinvertebrates, and fish were analyzed for: 1) stable carbon (δ¹³ C) and nitrogen (δ¹⁵ N) isotope ratios to delineate food webs, and 2) total Hg (THg) or MeHg. Compared with the brook trout from reference lakes, fish from invaded lakes had higher length-standardized THg concentrations as well as a narrower dietary range and elevated trophic level, inferred from unadjusted δ¹³ C and δ¹⁵ N values, respectively. The rate of Hg biomagnification was similar across invaded and reference lakes, implying little effect of the invasive fish on the trophic transfer of MeHg. Despite differences in food web structure due to pearl dace invasion, DOC was the strongest predictor of brook trout THg levels for all lakes, suggesting that underlying environmental factors exerted a stronger influence on brook trout THg concentrations than the presence of a non-native forage fish. Environ Toxicol Chem 2020;39:2196-2207. © 2020 SETAC.

Climate and landscape conditions indirectly affect fish mercury levels by altering lake water chemistry and fish size

Mercury pollution is a global environmental problem that threatens ecosystems, and negatively impacts human health and well-being. Mercury accumulation in fish within freshwater lakes is a complex process that appears to be driven by factors such as individual fish biology and water chemistry at the lake-scale, whereas, climate, and land-use/land-cover conditions within lake catchments can be influential at relatively larger scales. Nevertheless, unravelling the intricate network of pathways that govern how lake-scale and large-scale factors interact to affect mercury levels in fish remains an important scientific challenge. Using structural equation models (SEMs) and multiple long-term databases we identified direct and indirect effects of lake-scale and larger-scale factors on mercury levels in Walleye and Northern Pike - two species that are valued in inland fisheries. At the lake-level, the most parsimonious path models contained direct effects of fish weight, DOC, and pH, as well as an indirect effect of DOC on fish mercury levels via fish weight. Interestingly, lakeshed-, climate-, and full-path models that combine the effects of both lakeshed and climate revealed indirect effects of surrounding landscape conditions and latitude via DOC, pH, and fish weight but no direct effects on fish mercury levels. These results are generally consistent across species and lakes, except for some differences between stratified and non-stratified lakes. Our findings imply that understanding climate and land-use driven alterations of water chemistry and fish biology will be critical to predicting and mitigating fish mercury bioaccumulation in the future.

A global-scale assessment of fish mercury concentrations and the identification of biological hotspots

We present data on a rapid assessment of fish Hg concentrations from 40 different waterbodies in 26 countries that includes data on 451 fish of 92 species. Significant differences in fish Hg concentrations were observed across fish foraging guilds and in general, higher trophic level fish (i.e., piscivores and carnivores) showed the highest mean total Hg (THg) concentrations. However, elevated THg concentrations observed in a lower trophic level, detrivorous species highlights the importance of understanding Hg concentrations across a wide range of trophic levels, and also characterizing site-specific processes that influence methylmercury (MeHg) bioavailability. A linear mixed effects model was used to evaluate the effects of length, trophic level, sampling location, and taxonomy on THg concentrations. A positive, significant relationship between THg in fish and fish size, trophic level, and latitude of the sampling site was observed. A comparison of Hg concentrations across all sites identifies biological mercury hotspots, as well as sites with reduced Hg concentrations relative to our overall sampling population mean Hg concentration. Results from this study highlight the value of rapid assessments on the availability of methylmercury in the environment using fish as bioindicators and the need for expanded biomonitoring efforts in understudied regions of the world. This study also provides insights for the future design and implementation of large-scale Hg biomonitoring efforts intended to evaluate the effectiveness of future Hg reduction strategies instituted by the Minamata Convention on Mercury.

Temporal trends, lake-to-lake variation, and climate effects on Arctic char (Salvelinus alpinus) mercury concentrations from six High Arctic lakes in Nunavut, Canada

Climate warming and mercury (Hg) are concurrently influencing Arctic ecosystems, altering their functioning and threatening food security. Non-anadromous Arctic char (Salvelinus alpinus) in small lakes were used to biomonitor these two anthropogenic stressors, because this iconic Arctic species is a long-lived top predator in relatively simple food webs, and yet population characteristics vary greatly, reflecting differences between lake systems. Mercury concentrations in six landlocked Arctic char populations on Cornwallis Island, Nunavut have been monitored as early as 1989, providing a novel dataset to examine differences in muscle [Hg] among char populations, temporal trends, and the relationship between climate patterns and Arctic char [Hg]. We found significant lake-to-lake differences in length-adjusted Arctic char muscle [Hg], which varied by up to 9-fold. Arctic char muscle [Hg] was significantly correlated to dissolved and particulate organic carbon concentrations in water; neither watershed area or vegetation cover explained differences. Three lakes exhibited significant temporal declines in length-adjusted [Hg] in Arctic char; the other three lakes had no significant trends. Though precipitation, temperature, wind speed, and sea ice duration were tested, no single climate variable was significantly correlated to length-adjusted [Hg] across populations. However, Arctic char Hg in Resolute Lake exhibited a significant correlation with sea ice duration, which is likely closely linked to lake ice duration, and which may impact Hg processing in lakes. Additionally, Arctic char [Hg] in Amituk Lake was significantly correlated to snow fall, which may be linked to Hg deposition. The lack of consistent temporal trends in neighboring char populations indicates that currently, within lake processes are the strongest drivers of [Hg] in char in the study lakes and potentially in other Arctic lakes, and that the influence of climate change will likely vary from lake to lake.

Factors influencing fish mercury concentrations in Iowa rivers

Fish mercury concentrations have received considerable attention due to human health implications. Fish mercury concentrations are variable within and among systems due to a suite of biotic and abiotic influences that vary among regions and are difficult to predict. Understanding factors associated with variability in fish mercury concentrations would help guide consumption advisories. Mercury concentrations in channel catfish (Ictalurus punctatus, n = 205), flathead catfish (Pylodictis olivaris, n = 123), northern pike (Esox lucius, n = 60), smallmouth bass (Micropterus dolomieu, n = 176), and walleye (Sander vitreus, n = 176) were assessed in ten Iowa rivers and relationships with land use, water chemistry, and fish characteristics were explored. Mercury concentrations were generally low (mean among all species = 0.17 mg/kg, n = 740) but higher in flathead catfish, northern pike, smallmouth bass, and walleye than channel catfish and were positively related to fish length, age, trophic position, and δ¹³C signatures. Phosphorus, sulfate, and percent open water and grassland were negatively related to fish mercury concentrations, whereas water hardness, nitrogen-ammonia, Human Threat Index, and percent wetland and forest were positively related to fish mercury concentrations. Fish collected from the Paleozoic Plateau ecoregion in northeast Iowa had higher mercury concentrations than other ecoregions in Iowa. Combined, these factors explained 70% of the variation in fish mercury concentrations. This study provides a comprehensive analysis of abiotic and biotic factors influencing fish mercury concentrations in lotic ecosystems at the individual and system scale that will help guide fish consumption advisories.

Does forest harvest increase the mercury concentrations in fish? Evidence from Swedish lakes

A number of studies have evaluated the effects of forest harvest on mercury (Hg) concentrations and exports in surface waters, but few studies have tested the effect from forest harvest on the change in fish Hg concentrations over the course of several years after harvest. To address this question, mercury (Hg) concentrations in perch (Perca fluviatilis) muscle tissue from five lakes were analyzed for two years before (2010-2011) and three years after (2013-2015) forest harvest conducted in 2012. Fish Hg concentrations in the clear-cut catchments (n=1373 fish specimens) were related to temporal changes of fish Hg in reference lakes (n=1099 fish specimen) from 19 lakes in the Swedish National Environmental Monitoring Programme. Small (length<100mm) and large perch (length≥100mm) were analyzed separately, due to changing feeding habitats of fish over growing size. There was considerable year-to-year and lake-to-lake variation in fish Hg concentrations (-14%-121%) after forest harvest in the clearcut lakes, according to our first statistical model that count for fish Hg changes. While the effect ascribed to forest harvest varied between years, after three years (in 2015), a significant increase of 26% (p<0.0001) in Hg concentrations of large fish was identified in our second statistical model that pooled all 5 clearcut lakes. The large fish Hg concentrations in the 19 reference lakes also varied, and in 2015 had decreased by 7% (p=0.03) relative to the concentrations in 2010-2011. The majority of the annual changes in fish Hg concentrations in the clearcut lakes after harvest were in the lower range of earlier predictions for high-latitude lakes extrapolated primarily from the effects of forest harvest operations on Hg concentrations in water. Since the risk of forest harvest impacts on Hg extends to fish and not just surface water concentrations, there is even more reason to consider Hg effects in forestry planning, alongside other ecosystem effects.

Heavy metals and minerals contents in pikeperch (Sander lucioperca), carp (Cyprinus carpio) and flathead grey mullet (Mugil cephalus) from Sidi Salem Reservoir (Tunisia): health risk assessment related to fish consumption

The aim of this study was to investigate heavy metals and selected minerals contents in filets of pikeperch (Sander lucioperca), carp (Cyprinus carpio) and flathead grey mullet (Mugil cephalus), the major fish species produced in Sidi-Salem reservoir; the largest Tunisian freshwater ecosystem. Concentrations of Ca, Mg, Fe, Zn, Cd, Pb and Hg were determined by inductively coupled plasma-optical emission spectrometry, while concentrations of Na and P were determined by flame photometry and spectrophotometry, respectively. Results concerning heavy metals are considered quantitatively reliable for Hg and Cd but must be taken with precautions concerning Pb levels as the LOD (limit of detection) of the analytical process was higher than acceptable limit. They showed greater accumulations of both Hg and Cd in filets of pikeperch than in filets of carp and mullet, but none of the values exceeded the normative maximum levels (0.500 and 0.050 mg kg^-1 w.w., respectively). Considering provisional intakes, target hazard quotient and hazard index, estimated for a fish portion per week, consumption of any of the species did not appear to be potentially hazardous for the health as they were far below threshold values. A fish portion would provide substantial amounts (>15% of daily requirements) in essential mineral nutrients (P, Mg and Fe) and thus should be considered an interesting contribution to a healthy diet. It is strongly advocated to authorities including freshwater fish in the official national annual control survey of contaminants in fishery products, which in addition to guaranteeing security of consumers, would also allow diversifying valorisation opportunities and thus increase the economic value of this fish production.

Mercury concentrations in fish from three major lakes in north Mississippi: Spatial and temporal differences and human health risk assessment

The goal of this study was to compare total mercury (Hg) concentrations in fish muscle tissue and assess consumption health risks of fish collected from three north Mississippi lakes (Sardis, Enid, and Grenada) that are extensively used for fishing and recreation. Largemouth bass (LMB; n = 64), channel catfish (CC; n = 72), and white crappie (WC; n = 100), which represent a range of trophic levels, were collected during spring 2013 and 2014. Creel data estimated that anglers harvested approximately 370,000 kg of WC, 27,000 kg of CC, and 15,000 kg of LMB from the lakes annually. Median Hg wet weight concentrations were highest in LMB (443 ng/g), followed by CC (211 ng/g) and WC (192 ng/g). Fish-Hg concentrations were lower than those reported in fish >10 years ago. There were significant differences between lakes consistent across species. Grenada length-normalized fish-Hg concentrations were higher than those from Enid and Sardis. Because existing consumption advisories for CC are length based, the lack of relationship between length and Hg concentration indicated that the recommendations may not be sufficiently protective. Further, five different risk assessment paradigms yielded hazard quotient (HQ) values suggesting that existing fish consumption advisories may be insufficient to protect adults and especially children from exposure to Hg.

Effects of habitat on mercury concentrations in fish: a case study of Nile perch (Lates niloticus) in Lake Nabugabo, Uganda

This study focused on variation in fish mercury (Hg) concentrations in 185 Nile perch (Lates niloticus) samples collected across four different habitat types in Lake Nabugabo, Uganda, a tropical lake located proximate to Lake Victoria. We quantified the stomach contents of Nile perch using the % index of relative importance, as well as, nitrogen and carbon isotopic concentrations to assess the role of diet and trophic level on Hg concentrations. In each habitat, we also evaluated a suite of chemical and physical characteristics that are commonly associated with variation in Hg bioavailability in temperate systems. Using linear mixed models and ANOVA, we demonstrate that habitat of capture is an important predictor of Hg concentrations in Nile perch from Lake Nabugabo and that the relationship between habitat and Hg is size and diet dependent. Nile perch diet as well as dissolved oxygen concentration and pH were also correlated with observed differences in fish Hg. Overall, Hg concentrations in Nile perch were all well below the WHO/FAO recommended guideline of 500 ng/g (mean 13.6 ± 0.4 ng/g wet weight; range 4.9 and 29.3 ng/g wet weight). This work contributes to a growing awareness of intra-lake divergence in Nile perch, as well as, divergence in Hg concentrations between varying aquatic habitat types, particularly wetlands.

Species-specific mercury bioaccumulation in a diverse fish community

Mercury bioaccumulation models developed for fish provide insight into the sources and transfer of Hg within ecosystems. Mercury concentrations were assessed for 16 fish species of the western reach of Lake Diefenbaker, Saskatchewan, Canada. For top predators (northern pike, Esox Lucius; walleye, Sander vitreum), Hg concentrations were positively correlated to δ(15)N, and δ(15)N to fish age, suggesting that throughout life these fish fed on organisms with increasingly higher trophic values and Hg concentrations. However, fish mass and/or age were the principal parameters related to Hg concentrations for most species. For 9 common species combined, individual variation in Hg concentration was explained in declining order of importance by fish mass, trophic position (δ(15)N), and fish age. Delta (15)N value was not the leading variable related to Hg concentration for the assemblage, probably because of the longevity of lower--trophic-level species (3 species ≥ 20 yr), substantial overlap in Hg concentration and δ(15)N values for large-bodied fish up to 3000 g, and complex relationships between Hg concentration and δ(15)N among species. These results suggest that the quantity of food (and Hg) consumed each year and converted to fish mass, the quantity of Hg bioaccumulated over years and decades, and trophic position were significant determinants of Hg concentration in Lake Diefenbaker fish.

Bioaccumulation and biomagnification of mercury in African lakes: the importance of trophic status

Despite the global prevalence of both mercury (Hg) contamination and anthropogenic eutrophication, relatively little is known about the behavior of Hg in eutrophic and hypereutrophic systems or the effects of lake trophic status on Hg uptake and trophodynamics. In the current study we explore Hg trophodynamics at 8 tropical East African study sites ranging from mesotrophic to hypereutrophic, in order to assess the influence of lake trophic status on Hg uptake and biomagnification. Comprehensive water, plankton and fish samples were collected for analysis of total mercury (THg) and stable carbon and nitrogen isotopic ratios. We found evidence that uptake of THg into phytoplankton tended to be lower in higher productivity systems. THg concentrations in fish were generally low, and THg trophic magnification factors (TMFs; representing the average increase in contaminant concentrations from one trophic level to the next) ranged from 1.9 to 5.6. Furthermore TMFs were significantly lower in hypereutrophic lakes than in meso- and eutrophic lakes, and were negatively related to chlorophyll a concentrations both across our study lakes, and across African lakes for which literature data were available. These observations suggest that THg concentrations were strongly influenced by trophic status, with year-round high phytoplankton and fish growth rates reducing the potential for high THg in fish in these productive tropical lakes.

Spatial trends and factors affecting mercury bioaccumulation in freshwater fishes of Washington State, USA

Twenty-four lakes in Washington State, United States, were sampled for largemouth and smallmouth bass as well as water chemistry parameters during 2005 to 2009 to evaluate trends in mercury (Hg) concentrations. We analyzed spatial patterns in bass Hg levels across a gradient of land and climate types, lake chemistry parameters, and physical watershed characteristics to identify factors influencing Hg bioaccumulation. Across the state, bass Hg levels followed rainfall patterns and were statistically greater on the coastal west side of the state and lowest in the drier eastern region. Lake and watershed variables with the strongest correlations to Hg bioaccumulation in bass were annual watershed precipitation (+) and lake alkalinity (-). Principal component analysis (PCA) explaining 50.3 % of the variance in the dataset indicated that wet, forested landscapes were more likely to contain lakes with greater fish Hg levels than alkaline lakes in drier agriculture-dominated or open space areas. The PCA did not show wetland abundance and lake DOC levels as variables influencing bass Hg levels, but these were generally associated with small, shallow lakes containing greater chlorophyll levels. The effect of in-lake productivity may have counteracted the role of wetlands in Hg bioaccumulation among this study's lakes.

Nationwide monitoring of mercury in wild and farmed fish from fresh and coastal waters of Korea

Mercury (Hg) concentrations were monitored in wild and cultured fish collected from fresh and coastal waters in the Korean peninsula from April 2006 to August 2008 nationwide. Total Hg concentrations were reported for 5043 fish samples, including 78 species from 133 locations. Significant interspecies variation was noted in the Hg levels. The average Hg concentration in each fish species ranged from 6.31 μg kg(-1) for mullet (Mugil cephalus) to 200 μg kg(-1) for mandarin fish (Siniperca scherzeri). Among the species collected, the maximum concentration of Hg, 1720 μg kg(-1), was measured in an Amur catfish (Silurus asotus). Only wild freshwater fish exceeded the WHO ingestion standard. Wild freshwater piscivorous fish samples from a large artificial upstream lake contained the highest Hg levels. Hg concentrations were compared between fish groups categorized as wild and farmed fish from freshwater and coastal waters. Although the wild freshwater fish had similar size ranges, their Hg concentrations were higher than those of the other groups. Compared to the feed of farmed marine and freshwater fishes, the prey of wild freshwater fish had a higher Hg concentration, and the total Hg concentrations in freshwater and associated sediment samples were higher than those in coastal water and associated sediment samples. In the freshwater environment, piscivorous fish bioaccumulated two times more Hg than carnivorous and omnivorous fish and four times more than planktivorous fish. The difference in Hg concentrations among trophic groups might have been due to differences in the size of fish, in addition to the variations among different trophic groups. These data will be useful for developing the fish consumption advisory as a management measure to reduce Hg exposure.

Do fish growth rates correlate with PCB body burdens?

We evaluated whether growth rates of six fish species correlated with PCB concentrations in a moderately-to-heavily polluted freshwater ecosystem. Using a large dataset (n = 984 individuals), and after accounting for growth effects related to fish age, habitat, sex, and lipids, growth correlated significantly, but positively with lipid-corrected PCB concentrations for 4 of 6 species. Remaining species showed no correlations between growth and PCBs. Comparisons with regional, lentic growth averages for four species confirmed growth was on par and in three of four cases higher than regional averages in the PCB-polluted ecosystem. We conclude that for these species, at the range of concentrations examined, these PCBs do not exert negative impacts on growth. Rather, factors often cited as influential to growth were also driving growth trends in this study. Future studies that evaluate whether pollution affects growth must account for major growth drivers prior to attributing growth differentials to pollution alone.