Mercury Concentrations In Muscle Tissue Research Articles

Comparison of carbon, nitrogen, and oxygen stable isotope ratios and mercury concentrations in muscle tissues of five beaked whale species and sperm whales stranded in Hokkaido, Japan

ABSTRACT We studied δ 13C, δ 15N and δ 18O values, and total mercury (THg) concentrations in muscle samples from deep-sea predators – five beaked whale species and sperm whales – stranded along the coast of Hokkaido, in the north of Japan in 2010 and 2019. The δ 13C, δ 15N and δ 18O values, THg concentrations, and body length (BL) of Stejneger’s beaked whales were similar to those of Hubbs’ beaked whales, which belong to the same genus. In contrast, δ 13C values, THg concentrations, and BL of Sato’s beaked whales were markedly different from those of Baird’s beaked whales, which belong to the same genus. Stejneger’s and Hubbs’ beaked whales living around Hokkaido may compete in their ecological niches, whereas Sato’s and Baird’s beaked whales may segregate their ecological niches. Although Cuvier’s beaked whales and sperm whales belong to different genera and their BLs were significantly different, their δ 13C and δ 15N values were similar, probably because they can dive and stay in deeper waters than other beaked whale species. The δ 13C values in combined samples from all whales increased with increasing BL, probably owing to the larger whale species’ dietary preference for squid. The δ 13C values in combined samples from all whales were positively correlated with THg concentrations, whereas the δ 15N values in the combined samples were negatively correlated. The δ 18O values in combined samples from most whales tended to be positively correlated with THg concentrations. These correlations may be explained by a higher THg load from deep-sea feeding than from pelagic feeding and by a feeding shift towards lower trophic levels.

High mercury concentrations in Atlantic Goliath Grouper: Spatial analysis of a vulnerable species

The Atlantic Goliath Grouper Epinephelus itajara is currently a protected species in the southeastern United States waters of the Atlantic and the Gulf of Mexico and is considered vulnerable throughout its geographic range. In this study, I evaluated mercury concentrations in their tissues (muscle, liver), which revealed high concentrations (μg/g ww) of mercury (mean ± SE) in liver (6.18 ± 0.86) and muscle (1.12 ± 0.06) tissue that increased with size and age. Mercury concentrations were highest in fish caught off Florida's Atlantic coast, but varied on a finer regional scale. Mercury concentrations in muscle tissue were generally greater near urbanized areas with known mercury sources and environmental conditions appropriate for higher methylation rates. This suggests that management should consider improving the water quality in these areas to reduce the risk of health effects to human consumers and to the fish themselves.

Mercury in fish products: what’s the best for consumers between bluefin tuna and yellowfin tuna?

A total of 205 bluefin and yellowfin tuna samples were examined for mercury detection in order to verify possible differences and have a detailed risk assessment of the two tuna species. The results showed significant higher mercury concentration in muscle tissue of bluefin tuna respect yellowfin tuna (p < 0.001) with mean concentration of 0.84 mg/kg and maximum value of 1.94 mg/kg. These differences can be due the different biological and ecological aspects of the two tuna species and to different oceanographic aspects between Atlantic Ocean and Mediterranean sea. The results obtained in this study suggest an advisable containment of the sources of pollution and further studies on the closed-loop farming of bluefin tuna, in order to ensure the product safety.

Organic and Total Mercury Concentration in Fish Muscle and Thermodynamic Study of Organic Mercury Extraction in Fish Protein

MeHg and total mercury concentrations were determined in the muscle tissues of four fish species (Cyprinus carpio, Rutilus frisii, Carassius auratus and Esox lucius) from Anzali wetland (Guilan, Iran). Fish with the highest amount of MeHg was selected to determine the thermodynamic parameters of MeHg extraction. The extractions process was performed in the range of temperatures 331.15 to 367.15 K and at atmospheric pressure. Results show the extraction of MeHg from SH groups of sulfhydryl proteins was an endothermic process with a positive value for entropy and Gibbs free energy changes at the room temperature. Significant difference was found between MeHg content at T=367.15 K and other temperatures. Correlation coefficients results showed that the mercury concentration in muscle tissue was significantly related to the length and weight of fish (p≤0.01). Also, thermodynamic parameters of methylmercury extractions had significant correlation (p≤0.05) with length and weight of the six fish specimen.

Mercury in Indigenous, Introduced and Farmed Fish from the Semiarid Region of the Jaguaribe River Basin, NE Brazil

Indigenous, introduced and farmed fish species were collected from the Jaguaribe Basin, NE Brazil to assess total and methyl mercury concentrations in muscle tissue and to determine its relationship with fish origin. The results obtained from introduced species were compared to the Hg content of their original area of occurrence, which is located in the Amazon region. Farmed and wild individuals of Oreochromis niloticus (tilapia) were also compared. Introduced species presented lower Hg contents compared to their Amazonian counterparts. Wild individuals of O. niloticus also presented higher Hg contents than farmed individuals with similar sizes. However, methyl Hg concentrations were not significantly different between the two groups. Total Hg and methyl Hg concentrations were higher in carnivorous species, especially those from the Amazon region, and surpassed the Brazilian guidelines for fish consumption. Based on their Hg content, Jaguaribe basin fish do not pose a significant threat to human consumption.

Mercury in Groupers and Sea Basses from the Gulf of Mexico: Relationships with Size, Age, and Feeding Ecology

AbstractWe analyzed total mercury concentration in muscle tissue of 15 serranid species (n = 1,401 fish) collected from the Gulf of Mexico and also developed a comprehensive model relating two commonly used mercury analysis methods. There was considerable interspecific and intraspecific variability in mercury within groupers and sea basses. Mean mercury concentration for individual species ranged from 0.03 to 0.91 mg/kg wet weight across all size ranges, and for legally harvestable grouper and sea bass concentrations were 0.32 mg/kg and 0.09 mg/kg, respectively. Mercury in individual fish ranged from 0.01 to 3.3 mg/kg. Approximately 23% of all grouper samples analyzed contained mercury at concentrations that exceeded the U.S. Environmental Protection Agency's methylmercury consumption guidance criterion for humans (0.3 mg/kg). Mercury in legally harvestable individuals of some species exceeded 0.5 mg/kg, and harvestable black grouper Mycteroperca bonaci had a mean mercury concentration greater than 1.0 mg/kg. A positive relationship was observed between total mercury content and both fish length and fish age. For species that feed principally on fishes (e.g., gag M. microlepis and scamp M. phenax), mean mercury concentration was greater than that for species that feed mainly on invertebrates (e.g., red grouper Epinephelus morio and sand perch Diplectrum formosum). Although overall mean mercury concentrations were relatively low, for six species the maximum mercury concentration was at a level that has been associated with sublethal effects on fish physiology and with human health risks. Current grouper management regulations in the Gulf of Mexico select for a fishery of the largest and oldest individuals, which have the greatest mercury burdens. The species‐ and size‐specific mercury data from this study can be used to inform at‐risk human populations, refine regional fish consumption advisories, and further our understanding of mercury bioaccumulation in these important fishery species.

Distribution of Mercury in Rainbow Trout Tissues at Embryo-Larval and Juvenile Stages

The aims of the study were to determine total mercury concentrations in “rainbow trout Oncorhynchus mykiss (Walbaum)” at their embryo-larval and juvenile stages and to assess mercury concentration dynamics in individual tissues. Samples of rainbow trout were collected at two-month intervals over a period of 18 months (one stock production cycle) at the Velká Losenice trout farm. Feedstuff samples were collected at the same time and analyzed for mercury concentrations. Tissue mercury concentrations were determined in muscle, liver, and kidneys. Analyses were performed using the AMA 254 atomic absorption spectrophotometer. The lowest mercury concentration was found in 14-day-old embryos (hard roe), and the highest concentrations in muscle tissue, liver, and kidneys at the end of monitoring, that is, in rainbow trout aged 18 months. The amount of mercury in feedstuffs showed an increasing trend and ranged between 0.0126 and 0.0859 mgkg−1. A significant effect (P < 0.001) of mercury intake on mercury concentrations in muscle tissue, liver, and kidneys was demonstrated. Muscle mercury concentrations in 18-month-old market-ready rainbow trout of 0.128 ± 0.048 mgkg−1 met the criteria for fish meat hygiene.

Mercury concentrations in muscle tissue from sportfish in Lake Mead, Nevada

The aim of this study was to determine the concentrations of mercury present in commonly consumed fish from Lake Mead and to identify if differences exist between the 4 major basins. To date, no formal study using US Environmental Protection Agency (USEPA) approved methodology has been conducted to quantify the amount of mercury present in fish tissue from Lake Mead. Largemouth bass (n = 49), striped bass (n = 94) and channel catfish (n = 78) were collected from selected sites in Boulder Basin, Overton Arm, Virgin Basin and Gregg Basin of Lake Mead. Muscle tissue was homogenized, digested and analyzed for mercury in accordance with USEPA Method 245.6. Mean total mercury concentrations were (± SD) 0.089 ± 0.065, 0.154 ± 0.127 and 0.098 ± 0.080 μg/g in largemouth bass, striped bass and channel catfish, respectively. There was a significant overall difference in mean mercury concentration between fish from the 4 major basins of Lake Mead (F3,208= 20.541, p < 0.001). The mean mercury concentration in Boulder Basin was significantly lower than all other locations (p < 0.001). Of 221 samples analyzed, 10 samples were found to have mean mercury concentrations above the USEPA's 2001 tissue residue criterion of 0.3 μg methlymercury/g fish tissue.

High levels of mercury in biota of a new Prairie irrigation reservoir with a simplified food web in Southern Alberta, Canada

This study examined mercury levels in northern pike (Esox lucius) from the Twin Valley Reservoir in southern Alberta, 2 years after construction in 2003. The hypothesis was tested that mercury concentrations in pike from the reservoir are significantly higher than in pike from the nearby Oldman River. Mercury concentrations in muscle tissue (0.37–1.54 ppm) generally exceeded the consumption guideline of 0.5 ppm total mercury (THg), and were significantly higher (3.5-fold) than northern pike mercury concentrations in the Oldman River. In addition, these levels exceeded (up to 2-fold) previously published data from other reservoirs of the northern hemisphere. Gill-netting followed by stomach contents and stable isotope analysis revealed a very simple food web. No zooplanktivorous fish species were present, and the benthic fish community contained only few white sucker (Catostomus commersoni). Thus, the reservoir almost completely lacked forage fish, and the pike fed primarily on amphipods (Gammarus lacustris and Hyalella azteca), whose average mercury concentrations were 0.21 ppm. An observed low growth trajectory of northern pike in this reservoir may reflect low growth efficiency as a result of their invertebrate diet.

Reduction of mercury levels in cultured bluefin tuna, Thunnus orientalis, using feed with relatively low mercury levels

The purpose of this study was to determine whether feeding cultured bluefin tuna with feed fish containing low levels of mercury results in a concomitant reduction in the total mercury levels in tuna. The control group was fed spotted mackerel with average mercury concentrations of 0.052 ppm, and the experimental group was fed horse mackerel in combination with Japanese sand lance, whose mercury concentrations were 0.016 ppm and 0.037 ppm (0.019 ppm in average), respectively. Mercury intake in the control and experimental groups' tunas decreased from 124 to 53 µg/kg body weight/month and from 60 to 19 µg/kg body weight/month over the duration of the 19- and 18 month rearing period, respectively. Three specimens from each group were harvested at approximately monthly intervals initially, and then less frequently as the tuna increased in size, and muscle tissue, internal organs, gill filaments, and blood samples were collected for analysis. In the control group, total mercury concentrations increased from 0.25 to 0.55 ppm in all muscle samples except the front ventral one. In contrast, total mercury concentrations in muscle tissues from the experimental group were less than 0.25 ppm, with no marked increases observed over time. The mercury concentrations of the internal organs in the experimental samples were also lower than those of the control.The study showed that feeding bluefin tuna horse mackerel supplemented with sand lance can decrease the accumulated total mercury levels lower than the maximum permitted level of mercury in fish in Japan (0.4 µg/g). This study is the first report to describe the production of bluefin tuna with such low levels of mercury.

Temporal and geographic trends in mercury concentrations in muscle tissue in five species of hudson river, USA, fish

AbstractWe analyzed a New York (USA) state database of mercury concentrations in muscle tissue for five species of fish (striped bass, yellow perch, largemouth bass, smallmouth bass, and carp) over a range of locations in the Hudson River (USA) between 1970 and 2004. We used regression models to discern temporal and geographic change in the fish while controlling for a positive correlation between mercury concentration and body mass. Mercury concentrations significantly increased in fish from New York Harbor waters to the mid‐Hudson River. Striped bass and yellow perch showed a shallower increase in mercury concentration with river mile than did carp, largemouth bass, and smallmouth bass. Mercury concentrations declined over the 34‐year period. These results imply that a geographically restricted source of mercury may be spread throughout the watershed by toxin‐laden dispersing species. The increase of mercury toward the north may relate to a point source in the mid‐Hudson River, or it may indicate mercury released from the Adirondack watershed. The decline of mercury over three decades corresponds to a reduction of various inputs in the region. The temporal and geographic pattern of mercury in sediments corresponds to the geographic trend of mercury in fish.

Temporal and Geographic Trends in Mercury Concentrations in Muscle Tissue in Five Species of Hudson River, USA, Fishes

We analyzed a New York (USA) state database of mercury concentrations in muscle tissue for five species of fish (striped bass, yellow perch, largemouth bass, smallmouth bass, and carp) over a range of locations in the Hudson River (USA) between 1970 and 2004. We used regression models to discern temporal and geographic change in the fish while controlling for a positive correlation between mercury concentration and body mass. Mercury concentrations significantly increased in fish from New York Harbor waters to the mid-Hudson River. Striped bass and yellow perch showed a shallower increase in mercury concentration with river mile than did carp, largemouth bass, and smallmouth bass. Mercury concentrations declined over the 34-year period. These results imply that a geographically restricted source of mercury may be spread throughout the watershed by toxin-laden dispersing species. The increase of mercury toward the north may relate to a point source in the mid-Hudson River, or it may indicate mercury released from the Adirondack watershed. The decline of mercury over three decades corresponds to a reduction of various inputs in the region. The temporal and geographic pattern of mercury in sediments corresponds to the geographic trend of mercury in fish.

Mercury Concentrations in Fish from Lake Meredith, Texas: Implications for the Issuance of Fish Consumption Advisories

We examined how length of fish is related to mercury concentrations in muscle tissue of seven species of fish from Lake Meredith, Texas and determined how sex and growth rate are related to mercury concentration in walleye (Sander vitreus). Flathead catfish (Pylodictis olivaris), walleye and white bass (Morone chrysops) had the highest concentrations of mercury and channel catfish (Ictalurus punctatus), common carp (Cyprinus carpio), river carpsucker (Carpiodes carpio) and gizzard shad (Dorosoma cepedianum) had the lowest concentrations of mercury. Mercury concentrations were positively correlated with total length (TL) of fish for all species except gizzard shad, which exhibited a negative correlation between mercury concentration and TL. Male walleye grew more slowly than females, and males had higher concentrations of mercury than females. We also assessed the differences in fish consumption advisories that would be issued using Texas Department of State Health Services (DSHS) guidelines versus United States Environmental Protection Agency (USEPA) recommendations. Using DSHS guidelines, no fish species in Lake Meredith would be issued a fish consumption advisory. Nevertheless, DSHS has issued an advisory for walleye in Lake Meredith, possibly due to an inadequate sample size of fish. Using USEPA guidelines, a fish consumption advisory would be issued for the largest size class of flathead catfish but no advisory exists for flathead catfish in Lake Meredith. We suggest that when fish in a lake may be contaminated with mercury, all game fish in the lake should be assessed, and mercury advisories should take fish size into account.

Mercury distribution in the skin of beluga ( Delphinapterus leucas) and narwhal ( Monodon monoceros) from the Canadian Arctic and mercury burdens and excretion by moulting

Beluga and narwhal skin as a whole (in Inuktitut known as “muktuk”) is considered to be a delicacy by native Canadian and Greenland people. Individual strata of the skin, and muscle from 27 beluga from the western, and 20 narwhal from the eastern Canadian Arctic, were analyzed for mercury and the thickness and density of each skin layer was measured. Mercury was not uniformly distributed in the skin, but increased outwardly with each layer. The concentration was only 0.29 and 0.16 μg/g (wet wt) in the innermost layer (dermis) of belugas and narwhal respectively, and 1.5 and 1.4 μg/g (wet wt) in the outermost layer (degenerative epidermis) of beluga and narwhal, respectively. There was a significant ( α = 0.05) association between age and mercury concentration in each skin layer, the regression coefficients progressively increasing from the inner layer (dermis) to the outer layer: 0.011–0.063 μg/g year − 1 ; 0.034 μg/g year − 1 for skin as a whole; 0.054 μg/g year − 1 for muscle. The concentration of total mercury was 0.84 and 0.59 μg/g (wet wt) in skin as a whole (muktuk) of beluga and narwhal respectively, and 0.12 and 0.03 μg/g in blubber, respectively. The average, total mercury concentration in muscle tissue was 1.4 and 0.81 μg/g wet wt, in beluga and narwhal respectively, exceeding (except for blubber) the Canadian Government's Guideline (0.5 μg/g wet wt) for fish export and consumption. The skin surface area of an average-size beluga and narwhal was estimated (6.10 and 6.50 m 2, respectively), as were excretions of mercury through moulting (13,861 and 6721 μg year − 1 ; 14 and 7 mg year − 1 ) for belugas and narwhal, respectively. The whole-body mercury burden (699,300 μg; 700 mg) for a 1000 kg beluga and its various tissues were estimated, as was the fraction of mercury excreted by moulting (2–0.42% of the whole-body burden). Annual mercury burden increments in beluga skin, muscle and the whole body were estimated (2750; 17,280; 40,00 μg year − 1 , respectively), using regression coefficients of age on mercury concentration. The annual gross mercury intake via food was estimated (131,400 μg), of which 70% was excreted.

Total and organic mercury concentrations in muscle tissue of the blue shark ( Prionace glauca L.1758) from the Northeast Atlantic

Total and organic mercury concentrations in muscle tissue of the blue shark ( Prionace glauca L.1758) from the Northeast Atlantic

Total mercury concentrations in lakes and fish of western Maryland, USA.

The purpose of this study was to quantify total mercury concentrations in three species of fish in three lakes of western Maryland: Piney Creek reservoir, Deep Creek Lake, and Lake Habeeb. We measured total mercury concentrations in water from each lake and muscle tissue from 119 fish collected in fall 2000: 15 largemouth bass (Micropterus salmoides), 15 yellow perch (Perca flavescens), and 15 bluegill (Lepomis macrochirus) from the Piney Creek reservoir; 15 largemouth bass, 15 yellow perch, and 14 bluegill from Deep Creek Lake; and 15 largemouth bass and 15 bluegill from Lake Habeeb. Average total mercury concentrations (+/- SD) in surface waters were 0.96 +/- 0.03 ng L(-1) for the Piney Creek reservoir, 0.56 +/- 0.07 ng L(-1) for Deep Creek Lake, and 0.40 +/- 0.05 ng L(-1) for Lake Habeeb. These water quality differences were sometimes reflected in the total mercury concentration in fish muscle tissue. Total mercury concentrations in bluegill (0.05 +/- 0.02 microg g(-1)) and largemouth bass (0.10 +/- 0.03 microg g(-1)) from Lake Habeeb were significantly (p < 0.001) lower than the total mercury concentrations in bluegill and largemouth bass from the Piney Creek reservoir (bluegill: 0.13 +/- 0.04 microg g(-1) and largemouth bass: 0.37 +/- 0.18 microg g(-1)) and Deep Creek Lake (bluegill: 0.11 +/- 0.04 microg g(-1) and largemouth bass: 0.30 +/- 0.09 microg g(-1)). Yellow perch from the Piney Creek reservoir had significantly higher total mercury concentrations than yellow perch from Deep Creek Lake (0.20 +/- 0.08 microg g(-1) versus 0.13 +/- 0.04 microg g(-1)). In contrast, total mercury concentrations in largemouth bass from the Piney Creek reservoir and Deep Creek Lake were not significantly different. With the exception of largemouth bass from Lake Habeeb and yellow perch from Deep Creek Lake, there were relatively strong (r(2) > 0.39-0.79) log-log relationships between the size (weight and length) of the fish and total mercury concentrations in muscle tissue. The largest largemouth bass (> 800 g and > 38 cm) from both Deep Creek Lake and the Piney Creek reservoir had total mercury concentrations that exceeded the consumption advisory of 0.5 microg g(-1) that is used by many states and Canada. In contrast, total mercury concentrations in largemouth bass from Lake Habeeb did not exceed this consumption advisory. Our results suggest that fish consumption advisories are needed for largemouth bass in the Piney Creek reservoir and Deep Creek Lake.

Geographical differences of zinc, cadmium, mercury and selenium in polar bears ( Ursus maritimus) from Greenland

Muscle, liver, and kidney tissues from 100 polar bears ( Ursus maritimus) caught in the Avanersuaq area, north-west Greenland, and Ittoqqortoormiit area, central-east Greenland, were analysed for zinc, cadmium, mercury and selenium. The zinc concentrations in muscle and liver were higher than in kidney. Mean zinc concentrations ranged from 19.7 to 76.0 μg/g (all data are presented as geometric means on a wet wt. basis). The presented cadmium concentrations by area and age groups were all low in muscle and in many cases below the detection limit (range: <0.015–0.048 μg/g). Cadmium concentrations were intermediate in liver (range: 0.120–1.98 μg/g) and highest in kidney tissue (range: 2.16–28.9 μg/g). Mercury was likewise lowest in muscle tissue (range: 0.034–0.191 μg/g). Mercury concentration ranged quite similarly in liver and kidney tissue (liver range: 2.13–22.0 μg/g; kidney range: 2.87–32.0 μg/g). The selenium concentration increased from muscle (range:<0.2–0.452 μg/g) over liver (range: 1.20–9.80 μg/g) to kidney (range: 2.34–13.9 μg/g). No age accumulation was found for zinc. A weak increase was found for selenium, whereas cadmium and mercury clearly accumulated with age. An exception was mercury concentrations in muscle tissue, where no clear pattern was observed. Polar bears had significantly lower cadmium concentrations than ringed seals from the same area in all three tissues. Likewise mercury was significantly lower in the muscle tissue of polar bears than in ringed seals, whereas liver and kidney concentrations were higher. Biomagnification factors are provided for different tissues and age groups. Tissue ratios are given for different age groups and metals to enable a rough extrapolation from one tissue to another. Tissue ratios for cadmium, selenium and for mercury vary up to a factor of 6 with age. No significant differences could be detected between the elements analysed in bears from two management zones in north-west Greenland. This finding is in agreement with the genetic pattern in the two areas. In central-east Greenland, however, cadmium, selenium, and some of the mercury concentrations in polar bears from the southern area were higher than from the northern area, indicating that the east Greenland area represents two different ecological regions with different polar bear populations. Geographical differences between polar bears from north-west and east Greenland were only found for mercury and cadmium in liver tissue, where the concentrations were highest in bears from north-west Greenland. The geographical trend of increasing cadmium concentrations in polar bear liver tissue from west to east, which has been found previously in Canada, could be extended to cover north-west Greenland as well. East of this region a decrease was found. Mercury concentrations in polar bear liver tissue showed an increase from Svalbard over east and north-west Greenland, peaking in bears from SW Melville Island. A marked decrease was found west of Melville Island, and the lowest concentrations were found in the Chukchi Sea.

Comparative baseline levels of mercury, Hsp 70 and Hsp 60 in subsistence fish from the Yukon-Kuskokwim delta region of Alaska

In subsistence fish; northern pike ( Esox lucius), burbot ( Lota lota), whitefish ( Coregonus nelsoni), grayling ( Thymallus arcticus) and sheefish ( Stenodus lencichthys), we determined the Hsp 60 and Hsp 70 levels in 31 samples from adult fish gills. A dot-blot analysis using antibodies to either Hsp 70 or Hsp 60 showed the average Hsp 70 concentration was 9.1 μg/mg protein, while the average Hsp 60 concentration was 147.4 μg/mg protein. Mercury levels in muscle tissue in these fish averaged 0.382 ppm. Using a subset of samples ( n=24), we determined that the major component in the muscle of Alaskan subsistence fish was methyl mercury. No correlation was observed between Hsp 60 or Hsp 70 expression in gill tissue and mercury concentrations in muscle tissue. Hsp 60 and Hsp 70 protein levels in the gills were correlated.

Monitoring mercury in fish in a stream system receiving multiple industrial inputs

Sunfish and a minnow species were used as indicators of anthropogenic mercury contamination in an east Tennessee stream system receiving multiple point and non-point discharges. The monitoring of bluegill (Lepomis macrochirus) and redbreast sunfish (Lepomis auritus) identified bioavailable mercury near three geographically separate industrial facilities, and was able to detect decreases in contamination with distance away from these facilities. In general, total mercury concentrations in the tissue of sunfish in this study were low in comparison to the most commonly cited human health threshold limits, although concentrations at some sites exceeded 1 μg/g. Caged blacknose dace (Rhinichthys atratulus) were monitored in conjunction with resident fish as an indicator of more discrete sources in selected headwater streams where fish movement was deemed a potential factor affecting mercury body burdens. Mercury concentrations in muscle tissue of caged dace after 12 weeks exposure were generally low (<0.2 μg/g) at all sites but higher than in fish from reference streams. mercury accumulation varied between species (sunfish vs. dace) and monitoring method (caged vs. resident) at the same site, with sunfish tending to accumulate higher concentrations of mercury than resident dace which, in turn, contained about twofold higher concentrations than caged dace. However, the site-to-site pattern of mercury accumulation was similar. This study demonstrates the utility of using small stream dwelling fish with restricted home ranges as a tool for identifying and evaluating the bioavailability of mercury sources in large industrial or urbanized settings.

The role of dissolved organic carbon in the chemistry and bioavailability of mercury in remote Adirondack lakes

A number of recent studies have documented elevated concentrations of mercury (Hg) in fish caught in remote lakes and a pattern of increased concentrations of Hg in fish tissue with decreasing water column pH. Because of the potential linkage between fish Hg and surface water acidification, factors regulating water column concentrations and bioavailability of Hg were investigated in Adirondack lakes through a field study and application of the Mercury Cycling Model (MCM). Concentrations of total Hg and total MeHg were highly variable, with concentrations of total MeHg about 10% of total Hg in lakes which did not show anoxic conditions. In lakes exhibiting anoxic conditions in the hypolimnion during summer stratification, concentrations of total MeHg were elevated. Concentrations of total Hg and total MeHg increased with decreasing pH in remote Adirondack lakes. However, more importantly, concentrations of total Hg and total MeHg increased with increasing concentrations of dissolved organic carbon (DOC) and percent near-shore wetlands in the drainage basin. Mercury concentrations in muscle tissue of yellow perch from Adirondack lakes were elevated above the U.S. FDA action level (1 μg/g Hg) in 7% of the fish sampled or in one or more individual fish from 9 of the 16 lakes sampled. Fish Hg concentrations generally increased with increasing fish length, weight and age. Patterns of increasing Hg concentration with age likely reflect shifts in prey of yellow perch and the bioconcentration of Hg along the food chain. For age 3 to 5 perch, concentrations of Hg increased with increasing concentrations of DOC and percent near-shore wetlands in the drainage basin. However, for a lake with very high DOC concentrations, fish concentrations of Hg declined. Calculations with the MCM also show that concentrations of Hg species increase with increasing DOC due to complexation reactions. Increases in DOC result in increasing concentrations of Hg in biota but decreases in the bioconcentration factor of Hg in fish tissue. This research suggests that DOC is important in the transport of Hg to lake systems. High concentrations of DOC may complex MeHg, diminishing its bioavailability. At high concentrations of monomeric Al, the complexation of MeHg with DOC apparently decreases, enhancing the bioavailability of MeHg.