Mercury Concentrations In Fish Research Articles

Fish Tissue Mercury in Lakes and the Moderating Effects of Selenium

Fish mercury concentrations result in fish consumption advisories. However, selenium : mercury molar ratios >1 are protective to wildlife and humans. Therefore, we sampled total selenium (TSe) and total mercury (THg) concentrations and molar ratios in sport fish from 50 Idaho (ID) lakes >20 ha and 67 northeastern USA (NE) lakes >1 ha. Sample lakes were selected at random, to obtain unbiased estimates of mean fish tissue levels, with known confidence limits, for target populations of 95 ID lakes >20 ha in surface area and 12,557 NE lakes >1 ha. Bass and salmonids presented the greatest potential mercury toxicity risk to consumers based on their higher mercury content, desirability as game fish, and widespread distributions. Fish tissue THg exceeded safe consumption criteria in an estimated 20–80% of the lakes in the two regions and TSe exceeded safe consumption thresholds in an estimated 0–20% of the lakes in the two regions. However, the Se : Hg molar ratio was >1 in an estimated 90–97% of fish tested from NE and ID lakes. Therefore, we concluded that Se levels in these systems are usually sufficient to limit disruption of selenoprotein activities by Hg, and that fish consumption advisories based on Hg alone are unnecessarily restrictive.

Mercury Biogeochemistry and Biomagnification in the Mediterranean Sea: Current Knowledge and Future Prospects in the Context of Climate Change

In the 1970s, the discovery of much higher mercury (Hg) concentrations in Mediterranean fish than in related species of the same size from the Atlantic Ocean raised serious concerns about the possible health effects of neurotoxic monomethylmercury (MMHg) on end consumers. After 50 years, the cycling and fluxes of the different chemical forms of the metal between air, land, and marine environments are still not well defined. However, current knowledge indicates that the anomalous Hg accumulation in Mediterranean organisms is mainly due to the re-mineralization of organic material, which favors the activity of methylating microorganisms and increases MMHg concentrations in low-oxygen waters. The compound is efficiently bio-concentrated by very small phytoplankton cells, which develop in Mediterranean oligotrophic and phosphorous-limited waters and are then transferred to grazing zooplankton. The enhanced bioavailability of MMHg together with the slow growth of organisms and more complex and longer Mediterranean food webs could be responsible for its anomalous accumulation in tuna and other long-lived predatory species. The Mediterranean Sea is a “hotspot” of climate change and has a rich biodiversity, and the increasing temperature, salinity, acidification, and stratification of seawater will likely reduce primary production and change the composition of plankton communities. These changes will likely affect the accumulation of MMHg at lower trophic levels and the biomagnification of its concentrations along the food web; however, changes are difficult to predict. The increased evasion of gaseous elemental mercury (Hg°) from warming surface waters and lower primary productivity could decrease the Hg availability for biotic (and possibly abiotic) methylation processes, but lower oxygen concentrations in deep waters, more complex food webs, and the reduced growth of top predators could increase their MMHg content. Despite uncertainties, in Mediterranean regions historically affected by Hg inputs from anthropogenic and geogenic sources, such as those in the northwestern Mediterranean and the northern Adriatic Sea, rising seawater levels, river flooding, and storms will likely favor the mobilization of Hg and organic matter and will likely maintain high Hg bioaccumulation rates for a long time. Long-term studies will, therefore, be necessary to evaluate the impact of climate change on continental Hg inputs in the Mediterranean basin, on air–sea exchanges, on possible changes in the composition of biotic communities, and on MMHg formation and its biomagnification along food webs. In this context, to safeguard the health of heavy consumers of local seafood, it appears necessary to develop information campaigns, promote initiatives for the consumption of marine organisms at lower trophic levels, and organize large-scale surveys of Hg accumulation in the hair or urine of the most exposed population groups.

Mercury (Hg) concentration in fish commercialized in the São Luís fish market (MA) and potential exposure of consumers.

Fish consumption is the main path of human exposure to Hg and may represent a risk to public health, even with low Hg concentrations in fish, if consumption rates are high. This study quantifies, for the first time, the Hg concentrations in nine most commercialized species in the São Luís (MA) fish market, where fish consumption is high, and estimates human exposure. Average Hg concentrations were highest in carnivorous species, yellow hake (Cynoscion acoupa) (0.296 mg kg-1), the Atlantic croaker (Micropogonias undulatus) (0.263 mg kg-1), whereas lowest concentrations were recorded in iliophagous Mullets (Mugil curema) (0.021 mg kg-1) and the Shorthead drum Larimus breviceps (0.025 mg kg-1). Significant correlations were observed between Hg concentrations and fish length in two species: the Coco-Sea catfish (Bagre bagre) and the Atlantic bumper (Chloroscombrus crysurus), but not in the other species, since they presented relatively uniform size of individuals and/or a small number of samples. Risk coefficients, despite the relatively low Hg concentrations, suggest that consumers should limit their consumption of Yellow hake and Atlantic croaker, as they can present some risk to human health (EDI > RfD and THQ > 1), depending on the frequency of their consumption and the consumer's body weight.

Mercury (Hg) concentration in fish commercialized in the São Luís fish market (MA) and potential exposure of consumers

Mercury (Hg) concentration in fish commercialized in the São Luís fish market (MA) and potential exposure of consumers

Influence of a hydroelectric dam on fish mercury contamination along the Sinnamary River (French Guiana)

The Petit Saut hydroelectric dam and the upstream and downstream areas of the Sinnamary River in French Guiana (Amazon basin) have been studied from 1993 to 2020. The nearly thirty-years-long study of the monitoring of total mercury concentration in fish and the physicochemical survey of the environment made it possible to demonstrate the impact of the flooding of the forest and the role of the hydroelectric dam on the methylation of mercury. Results show that the physicochemical modifications generated by the construction of the dam led to a significant production of methylmercury (MeHg) in the anoxic part of the reservoir and downstream of the river leading to a strong spatio-temporal impact of the dam. Seven species of fishes are studied and their mercury concentrations vary according to many parameters: fish diet, position in the water column, site, lake oxycline level and time.

Reservoir Stratification Modulates the Influence of Impoundments on Fish Mercury Concentrations along an Arid Land River System.

Impoundment is among the most common hydrologic alterations with impacts on aquatic ecosystems that can include effects on mercury (Hg) cycling. However, landscape-scale differences in Hg bioaccumulation between reservoirs and other habitats are not well characterized nor are the processes driving these differences. We examined total Hg (THg) concentrations of Smallmouth Bass (Micropterus dolomieu) collected from reservoir, tailrace, and free-flowing reaches along an 863 km segment of the Snake River, USA, a semiarid river with 22 impoundments along its course. Across three size-classes (putative 1-year-old, first reproductive, and harvestable sized fish), THg concentrations in reservoirs and tailraces averaged 76% higher than those in free-flowing segments. Among reservoirs, THg concentrations were highest in reservoirs with inconsistent stratification patterns, 47% higher than annually stratified, and 144% higher than unstratified reservoirs. Fish THg concentrations in tailraces immediately downstream of stratified reservoirs were higher than those below unstratified (38-130%) or inconsistently stratified (32-79%) reservoirs. Stratification regimes influenced the exceedance of fish and human health benchmarks, with 52-80% of fish from stratifying reservoirs and downstream tailraces exceeding a human consumption benchmark, compared to 6-17% where stratification did not occur. These findings suggest that impoundment and stratification play important roles in determining the patterns of Hg exposure risk across the landscape.

Compound-specific stable isotopes of amino acids reveal influences of trophic level and primary production sources on mercury concentrations in fishes from the Aleutian Islands, Alaska

Total mercury concentrations ([THg]) exceed thresholds of concern in some Steller sea lion (Eumetopias jubatus) tissues from certain portions of the Aleutian Islands, Alaska. We applied compound-specific stable isotope analyses of both carbon and nitrogen in amino acids from fish muscle tissue to quantify the proportional contributions of primary production sources and trophic positions of eight prey species (n = 474 total) that are part of Steller sea lion diets. Previous THg analyses of fish muscle, coupled with monomethylmercury analyses of a subset of samples, substantiated previous findings that fishes from the west of Amchitka Pass, a discrete oceanographic boundary of the Aleutian Archipelago, have higher muscle Hg concentrations relative to fishes from the east. The δ13C values of essential amino acids (EAAs) in fish muscle demonstrated that although most fishes obtained their EAAs primarily from algae, some species varied in the extent to which they relied on this EAA source. The δ15N values of phenylalanine (0.9 to 7.8 ‰), an indicator of the isotopic baseline of a food web, varied widely within and among fish species. Trophic position estimates, accounting for this baseline variation, were higher from the west relative to the east of the pass for some fish species. Trophic magnification slopes using baseline-corrected trophic position estimates indicated similar rates of Hg biomagnification to the east and west of Amchitka Pass. Multiple linear regression models revealed that trophic position was the most important driver of fish muscle [THg] with less variation explained by other parameters. Thus, higher trophic positions but not the rate of Hg biomagnification to the west of Amchitka Pass may play a role in the regional differences in both fish and Steller sea lion [THg]. Although, differences in Hg contamination and uptake at the base of the east and west food webs could not be excluded.

Mercury distribution in fish organs sampled along the Mauritanian Atlantic coast and their potential human health risks

This paper aimed at assessing total mercury concentration in seven common fish species (Auxis rochei, Caranx rhonchus, Sardina pilchardus, Sardinella aurita, Sardinella maderensis, Scomber colias and Trachurus trecae) and a relationship between Hg organotropism and food regimes along the Mauritanian Atlantic coast. Results show that total mercury concentration in fish collected along five sites ranged from 0.027 to 0.533 mg/kg dry weight. Significant differences were observed among species depending on feeding behavior. Muscle tissues of carnivorous fish presented significantly higher levels of total mercury than that of omnivorous fish, except for Scomber colias, suggesting mercury biomagnification through the food chain. Significant differences in mercury concentrations were observed between muscle tissues and liver, for Auxis rochei, Trachurus trecae, and Caranx rhonchus.The mean concentrations in the different species are however low and none of the concentration values exceed the World Health Organization's threshold for human consumption.

Evaluating methods for determining mercury concentrations in ancient marine fish and mammal bones as an approach to assessing millennial-scale fluctuations in marine ecosystems

Millennial-scale datasets of heavy metals in biota are difficult to obtain but are important for determining patterns and underlying drivers of toxicant concentrations. This is particularly important to better discriminate contemporary natural and anthropogenic sources. Globally mercury is a contaminant of concern. Post-industrial increases in mercury in arctic biota have been documented and monitoring of Steller sea lions (Eumetopias jubatus) in the Aleutian Islands, Alaska, has revealed a high proportion of pups with fur mercury concentrations above thresholds of concern in some regions. As bone is a tissue that is well preserved in archeological middens, it may prove useful for developing long-term mercury data sets under appropriate conditions. The goal of this study was to evaluate methodologies for measuring mercury concentration in Steller sea lion bone using a direct mercury analyzer, considering sample preparation methods and variability among bone tissue types (e.g., compact versus spongy bone). Finally, we directly compare sensitivity and precision of two different direct mercury analyzer models. Based on the methods presented here, direct mercury analysis using the Nippon MA-3000 can quantify small (ppb) quantities of Hg accurately and precisely in 20 to 60mg of bone with minimal specimen processing. The described method is efficient, relatively inexpensive, and requires minimal bone, conserving rare and valuable specimens. Hydrogen peroxide cleaning and collagen extraction were not required, and may be detrimental for optimal Hg quantification in bone. Further, while homogenization of distinct compact and spongy bone did not impact concentration determination, variance of technical replicates was lower improving quantitation precision. Most importantly, significant differences between compact and spongy bone exist within some individual specimen; however, the difference is not consistent and may indicate differential Hg exposure windows influenced by turnover rate of bone types. We conclude bone provides a natural archive for mercury ecosystem dynamics over millennial time scales in regions where appropriate samples are available. Compact bone has lower and less variable [THg] simplifying analysis and interpretation of data; however, the more dynamic concentrations observed in spongy bone should not be dismissed as invaluable due to their variability in [THg]. Comparisons of [THg] between bone type within individual may provide insight into more acute changes in mercury exposure within an individual’s lifetime.

Relationship of mercury and selenium in ocean fish frequently consumed in the Seychelles: A comparison to levels in ocean fish consumed in the US

We characterized mercury and selenium in the fish consumed in the Seychelles Islands to determine if their levels are similar to fish consumed in the US. A secondary aim was to examine whether fish weight and species predict mercury and selenium in fish consumed in the Seychelles. We measured total mercury (THg) and selenium (Se) content of 10 samples from each of the 19 most frequently consumed fish species in Seychelles and for each calculated the Se:Hg molar ratios and the Selenium Health Benefit Value Index (HBV Se). Linear regression models examined associations with weight and species. Average MeHg levels in fish ranged from less than 0.01 ppm (streamlined spinefoot) to 0.7 ppm (bludger trevally) with an overall mean of 0.21 ± 0.23 ppm. Average Se levels ranged from 0.34 ppm (blue-barred parrot fish) to 0.93 ppm (blue-lined large-eye bream) with a mean of 0.54 ± 0.23 ppm. All fish species had a mean Se:Hg molar ratio > 1 and positive mean HBV Se index values. Weight was strongly predictive of MeHg and Se:Hg molar ratio, both across and within most species, but was less predictive of Se and HBV Se. Our study demonstrated that fish consumed in Seychelles have mercury and selenium content similar to that of fish consumed in the US. Fish in both countries have favorable positive values for Se:Hg molar ratios and HBV Se indexes. Because mercury and selenium concentrations in fish are similar to those in the US but fish consumption is substantially higher in Seychelles, the Seychellois make an ideal population in which to determine if there are adverse effects of prenatal, postnatal, and lifetime low dose MeHg exposure from fish consumption.

Proportional Hazard Bivariate Kumaraswamy Model Applied on Fish Mercury Concentration

Proportional Hazard Bivariate Kumaraswamy Model Applied on Fish Mercury Concentration

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.

The nutritional quality and contents of heavy elements due to thermal processing and storage in canned Thunnus tonggol fish change compared to fresh fish.

The purpose of this study was to evaluate the nutritional quality and concentration of heavy and toxic metals in the fresh and canned tuna Thunnus tonggol at different storage periods. The content of iron, zinc, copper, mercury, and also macronutrient compounds in the Iranian fresh and canned tuna fish and the effects of thermal processing and subsequent storage on metal contents were evaluated using atomic absorption spectroscopy. The results showed that the levels of iron, zinc, copper, and mercury after the 6th, 9th, and 11th months of storage were 26.52, 10.83, 6.22, and 0.04 mg/kg, respectively. The concentrations of iron, zinc, copper, and mercury in the fresh fish were 11.03, 7.11, 1.71, and 0.03 mg/kg, respectively. The results of the statistical analysis of the samples showed that canning process and sterilization by autoclave increased the contents of elements except mercury to a significant level (p < .05). The results showed that the amount of fat significantly increased in all samples after storage (p < .05), but the ash and protein content significantly decreased (p < .05). The moisture content significantly increased (p < .05) except for the 9th month of storage. The obtained results showed that the energy value after 6 months of storage was the highest (297.53 kcal/100 g). The results showed that the bioaccumulation of copper, iron, zinc, and mercury in the fresh and canned muscles was lower than the standard concentration recommended by the FAO and WHO. This type of fish was a high-quality food source and it was safe after 11 months of storage and was suitable for human consumption. Therefore, the consumption of Iranian canned tuna can be safe for human health despite the possible contamination with heavy metals.

A dynamic integrated model for mercury bioaccumulation in marine organisms

A novel integrated dynamic model, the Integrated Fish Model (INTFISH), incorporating mercury (Hg) dynamics at non-steady state in marine organisms, is presented and is applied to the benthic food web in a polluted area. The integrated Fish model represents the dynamics of inorganic mercury (HgII) and methyl‑mercury (MeHg) in a real marine ecosystem including environmental (seawater and sediments) and biota compartments. Mercury concentration in fish is estimated using the INTFISH model coupled, in real-time, with results from i) the seawater and sediments modules computed using the HR3DHG model, ii) a dedicated Phytoplankton model and iii) six modules for Hg fluxes within the invertebrate compartment, incorporating the main organisms included in fish diet preferences, whose variations during the whole life cycle are also taken into account to verify the sensitivity of the integrated model to the core set of parameters. The simulated total mercury concentrations (HgTOT) in specimens of red mullet (Mullus barbatus), selected as target species for the Fish model, are in excellent agreement with field observations reported from the investigated area. The intrinsic modularity of the model offers the opportunity to extend simulations to other fish species (which are part of the diet of human populations of interest) and predict Hg concentration in food. A natural extension of the model will allow to evaluate the health risks related to human consumption of contaminated fish.

Analysis of the results of research into the mercury content in fish and seafood during import-export operations in Ukraine for 2019–2021

The article presents the results of research on the determination of mercury in fish muscles and seafood, conducted based on the State Research Institute for Laboratory Diagnostics and Veterinary-Sanitary Examination by the Atomic Absorption Spectrometry Laboratory as systematic research in the period from 2019 to 2021. Mercury content in fish muscles was determined by atomic absorption spectrometry with direct sample injection. The study was carried out using a Milestone DMA-80 atomic absorption spectrophotometer (Italy). Certified standard samples (MERK) of mercury ion solution composition with an accredited value of 1.0 mg/cm2 were used to construct the calibration curves. The detection limits of mercury in fish and seafood are determined according to the validation data: the LOD detection limit is 0.1 μg/kg, and the LOQ detection limit is 5.0 μg/kg. During the studied period, research was carried out on 3368 samples of fish products: 2587 samples of sea fish, 161 samples of freshwater fish, 130 samples of other types of fish and seafood – 490 pieces, of which four examples of sea fish, namely fish of the tuna family, were found to exceed the maximum permissible level of mercury, which is 0.12% of the total number of studied samples. The mercury content in tuna muscles ranged from 0.356 to 1.889 mg/kg, 1.8 times higher than the MDR. It was found that the average mercury content in the muscles of freshwater fish was 0.006–0.315 mg/kg, which is significantly lower than the average mercury concentration in marine fish. The mercury concentration in the muscles of other types of fish and seafood was 0.008–0.472 mg/kg and did not exceed the regulated norms.

Investigating effects of climate-induced changes in water temperature and diet on mercury concentrations in an Arctic freshwater forage fish

The amount of mercury (Hg) in Arctic lake food webs is, and will continue to be, affected by rapid, ongoing climate change. At warmer temperatures, fish require more energy to sustain growth; changes in their metabolic rates and consuming prey with potentially higher Hg concentrations could result in increased Hg accumulation. To examine the potential implications of climate warming on forage fish Hg accumulation in Arctic lakes, we quantified growth and Hg accumulation in Ninespine Stickleback Pungitius pungitius under different temperature and diet scenarios using bioenergetics models. Four scenarios were considered that examined the role of climate, diet, climate × diet, and climate × diet × elevated prey Hg. As expected, annual fish growth increased with warmer temperatures, but growth rates and Hg accumulation were largely diet dependent. Compared to current growth rates of 0.3 g⋅y−1, fish growth increased at least 200% for fish consuming energy-dense benthic prey and decreased at least 40% for fish consuming pelagic prey. Compared to baseline levels, the Hg burden per kilocalorie of Ninespine Stickleback declined up to 43% with benthic consumption – indicating strong somatic growth dilution – but no more than 4% with pelagic consumption; elevated prey Hg concentrations led to moderate Hg declines in benthic-foraging fish and Hg increases in pelagic-foraging fish. Bioenergetics models demonstrated the complex interaction of water temperature, growth, prey proportions, and prey Hg concentrations that respond to climate change. Further work is needed to resolve mechanisms and rates linking climate change to Hg availability and uptake in Arctic freshwater systems.

Total mercury, methylmercury, and selenium concentrations in blue marlin Makaira nigricans from a long-term dataset in the western north Atlantic

Mercury in seafood is a neurotoxicant that threatens human health. Dynamic rates of mercury emission, re-emission, and atmospheric deposition warrant studies into mercury concentrations in fish because many are consumed by humans and can serve as sentinels of mercury levels in the environment. We modeled trends in total mercury content in an apex marine fish predator, Atlantic blue marlin Makaira nigricans, whose muscle tissues were opportunistically sampled from North Carolina (USA) sportfishing tournaments over a discontinuous time period: between 1975 and 77 and 1998–2021 (n = 148). The model-estimated influence of marlin weight on total mercury concentration was constant across years (shared slope) allowing for comparisons of weight-corrected mercury concentrations among years. Weight-corrected total mercury concentrations revealed an inter-decadal decline of approximately 45 % between the 1970s and late 1990s and then variable but relatively stable concentrations through 2021. The mean (SD) wet weight concentration of total mercury was 9.47 (4.11) from 1975 to 77 and 4.17 (2.61) from 2020 to 2021. Methylmercury and selenium were measured on a subset of fish to address questions related to human health and consumption. Methylmercury levels (mean = 0.72 μg/g) were much lower than total mercury (mean = 4.69 μg/g) indicating that total mercury is not a good proxy for methylmercury in Atlantic blue marlin. Selenium, examined as a Se:Hg molar ratio and as a selenium health benefit value (HBVSe), showed high protective value against mercury toxicity. Long-term trends in the concentration of mercury in blue marlin should continue to be monitored to determine whether policies to mitigate anthropogenic contributions to global mercury are achieving their intended goals and to provide information to inform safe human consumption.

Flood-pulse and trophic position modulate mercury concentrations in fishes from an Amazon floodplain lake

Mercury (Hg) bioaccumulation can be influenced by biological characteristics (e.g., trophic position) and environmental changes (e.g., seasonal flood-pulse), as it can create site conditions conducive to methylation and alter the availability of food to biota. This study aimed to relate total mercury (THg) and methylmercury (MeHg) concentrations in fishes of an Amazonian lake (Catalão Lake) to their dietary changes during different hydrological seasons (rising-, high-, falling-, and low-water). Levels of THg, MeHg, and stable isotopes of nitrogen and carbon (δ15N and δ13C) were determined in the muscles of six fish species: Rhytiodus microlepis, Hemiodus sp., Triportheus albus, Anodus elongatus, Pellona flavipinnis and Acestrorhynchus falcirostris. Triportheusalbus, an omnivorous fish, showed a significant relationship between Hg concentrations and δ13C signatures (negative regression; THg: p = 0.0001 and MeHg: p = 0.0002), as well as between Hg and δ15N signatures (positive regression; THg: p = 0.003 and MeHg: p = 0.021), indicating that changes in feeding habits influenced the Hg concentrations in this species. The herbivorous R. microlepis presented the highest MeHg concentrations during the high-water season, reflecting Hg methylation in its diet (macrophyte roots) during flooded season. The piscivorous A. falcirostris had the lowest THg concentrations during this season because of lower prey availability. Slopes of the regressions between the Hg concentrations and δ15N values followed the sequence of rising- < high- < falling-water seasons (THg: 0.06 < 0.11< 0.15; MeHg: 0.07 < 0.10 < 0.17), indicating that the difference between the THg and MeHg concentrations observed for lower- and higher-trophic-level fish increased during the falling-water season, resulting in trophic biomagnification. The present study shows that feeding habit and the flood-pulse influence mercury concentrations in the muscle of fishes from Catalão Lake.

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 (< 0.05mg/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.