Mercury Concentrations In Tissues Research Articles

A dynamic model using monitoring data and watershed characteristics to project fish tissue mercury concentrations in stream systems

A complex interplay of factors determines the degree of bioaccumulation of Hg in fish in any particular basin. Although certain watershed characteristics have been associated with higher or lower bioaccumulation rates, the relationships between these characteristics are poorly understood. To add to this understanding, a dynamic model was built to examine these relationships in stream systems. The model follows Hg from the water column, through microbial conversion and subsequent concentration, through the food web to piscivorous fish. The model was calibrated to 7 basins in Kentucky and further evaluated by comparing output to 7 sites in, or proximal to, the Ohio River Valley, an underrepresented region in the bioaccumulation literature. Water quality and basin characteristics were inputs into the model, with tissue concentrations of Hg of generic trophic level 3, 3.5, and 4 fish the output. Regulatory and monitoring data were used to calibrate and evaluate the model. Mean average prediction error for Kentucky sites was 26%, whereas mean error for evaluation sites was 51%. Variability within natural systems can be substantial and was quantified for fish tissue by analysis of the US Geological Survey National Fish Database. This analysis pointed to the need for more systematic sampling of fish tissue. Analysis of model output indicated that parameters that had the greatest impact on bioaccumulation influenced the system at several points. These parameters included forested and wetlands coverage and nutrient levels. Factors that were less sensitive modified the system at only 1 point and included the unfiltered total Hg input and the portion of the basin that is developed.

Oyster Saccostrea cucullata as a Biomonitor for Hg Contamination and the Risk to Humans on the Coast of Qeshm Island, Persian Gulf, Iran

A total of 174 individuals of rocky oysters (Saccostrea cucullata) and 35 surface sediment samples were collected from seven stations off the intertidal zones of Qeshm Island, Persian Gulf, in order to study the concentration of mercury in oysters' tissues, and to investigate whether mercury concentrations in the edible soft tissues are within the permissible limits for public health. The average mercury concentrations were found as 3.44, 50.66 and 2.29 μg kg(-1) dw in the sediments, soft tissues and shells of the oysters, respectively. Results indicated that the levels of mercury in sediment differed significantly between the stations. In addition, results confirmed that the soft tissues of oysters could be a good indicator of mercury in the aquatic system. In comparison with food safety standards, mercury levels in oysters were well within the permissible limits for human consumption.

Mercury in Nelson's Sparrow Subspecies at Breeding Sites

BackgroundMercury is a persistent, biomagnifying contaminant that can cause negative effects on ecosystems. Marshes are often areas of relatively high mercury methylation and bioaccumulation. Nelson's Sparrows (Ammodramus nelsoni) use marsh habitats year-round and have been documented to exhibit tissue mercury concentrations that exceed negative effects thresholds. We sought to further characterize the potential risk of Nelson's Sparrows to mercury exposure by sampling individuals from sites within the range of each of its subspecies.Methodology/Principal FindingsFrom 2009 to 2011, we captured adult Nelson's Sparrows at sites within the breeding range of each subspecies (A. n. nelsoni: Grand Forks and Upham, North Dakota; A. n. alterus: Moosonee, Ontario; and A. n. subvirgatus: Grand Manan Island, New Brunswick) and sampled breast feathers, the first primary feather (P1), and blood for total mercury analysis. Mean blood mercury in nelsoni individuals captured near Grand Forks ranged from 0.84±0.37 to 1.65±1.02 SD ppm among years, between 2.0 and 4.9 times as high as concentrations at the other sites (P<0.01). Breast feather mercury did not vary among sites within a given sampling year (site means ranged from 0.98±0.69 to 2.71±2.93 ppm). Mean P1 mercury in alterus (2.96±1.84 ppm fw) was significantly lower than in any other sampled population (5.25±2.24–6.77±3.51 ppm; P≤0.03).Conclusions/SignificanceOur study further characterized mercury in Nelson's Sparrows near Grand Forks; we documented localized and potentially harmful mercury concentrations, indicating that this area may represent a biological mercury hotspot. This finding warrants further research to determine if wildlife populations of conservation or recreational interest in this area may be experiencing negative effects due to mercury exposure. We present preliminary conclusions about the risk of each sampled population to mercury exposure.

Elevated mercury exposure and neurochemical alterations in little brown bats (Myotis lucifugus) from a site with historical mercury contamination

Despite evidence of persistent methylmercury (MeHg) contamination in the South River (Virginia, USA) ecosystem, there is little information concerning MeHg-associated neurological impacts in resident wildlife. Here we determined mercury (Hg) concentrations in tissues of insectivorous little brown bats (Myotis lucifugus) collected from a reference site and a MeHg-contaminated site in the South River ecosystem. We also explored whether neurochemical biomarkers (monoamine oxidase, MAO; acetylcholinesterase, ChE; muscarinic acetylcholine receptor, mAChR; N-methyl-D-aspartate receptor, NMDAR) previously shown to be altered by MeHg in other wildlife were associated with brain Hg levels in these bats. Concentrations of Hg (total and MeHg) in tissues were significantly higher (10-40 fold difference) in South River bats when compared to reference sites. Mean tissue mercury levels (71.9 ppm dw in liver, 7.14 ppm dw in brain, 132 ppm fw in fur) in the South River bats exceed (sub)-clinical thresholds in mammals. When compared to the South River bats, animals from the reference site showed a greater ability to demethylate MeHg in brain (33.1% of total Hg was MeHg vs. 65.5%) and liver (8.9% of total Hg was MeHg vs. 50.8%) thus suggesting differences in their ability to detoxify and eliminate Hg. In terms of Hg-associated neurochemical biomarker responses, interesting biphasic responses were observed with an inflection point between 1 and 5 ppm dw in the brain. In the reference bats Hg-associated decreases in MAO (r = -0.61; p < 0.05) and ChE (r = -0.79; p < 0.01) were found in a manner expected but these were not found in the bats from the contaminated site. Owing to high Hg exposures, differences in Hg metabolism, and the importance of the aforementioned neurochemicals in multiple facets of animal health, altered or perhaps even a lack of expected neurochemical responses in Hg-contaminated bats raise questions about the ecological and physiological impacts of Hg on the bat population as well as the broader ecosystem in the South River.

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 in the pelagic food web of Lake Champlain.

Lake Champlain continues to experience mercury contamination resulting in public advisories to limit human consumption of top trophic level fish such as walleye. Prior research suggested that mercury levels in biota could be modified by differences in ecosystem productivity as well as mercury loadings. We investigated relationships between mercury in different trophic levels in Lake Champlain. We measured inorganic and methyl mercury in water, seston, and two size fractions of zooplankton from 13 sites representing a range of nutrient loading conditions and productivity. Biomass varied significantly across lake segments in all measured ecosystem compartments in response to significant differences in nutrient levels. Local environmental factors such as alkalinity influenced the partitioning of mercury between water and seston. Mercury incorporation into biota was influenced by the biomass and mercury content of different ecosystem strata. Pelagic fish tissue mercury was a function of fish length and the size of the mercury pool associated with large zooplankton. We used these observations to parameterize a model of mercury transfers in the Lake Champlain food web that accounts for ecosystem productivity effects. Simulations using the mercury trophic transfer model suggest that reductions of 25-75% in summertime dissolved eplimnetic total mercury will likely allow fish tissue mercury concentrations to drop to the target level of 0.3 μg g(-1) in a 40-cm fish in all lake segments. Changes in nutrient loading and ecosystem productivity in eutrophic segments may delay any response to reduced dissolved mercury and may result in increases in fish tissue mercury.

Cadmium, lead, and mercury concentrations in tissues of roe deer (Capreolus capreolus L.) and wild boar (Sus scrofa L.) from Lowland Croatia

Cadmium, lead, and mercury concentrations were determined in roe deer and wild boar tissues (muscle, liver, kidney) of three different age groups from lowland Croatia. Cadmium concentrations in the examined tissues increased with age in both species, being the highest in the kidney, and higher in roe deer as compared to wild boar. Lead concentration was higher in younger animals in comparison with both older groups. Contrary to the expectations, roe deer tissues revealed mostly higher lead concentrations than those of wild boar. Mercury concentration in the tissues of the animals examined was relatively low and no correlation with age was found. However, mercury concentration was higher in kidney than in liver with both species. Wild boar had higher mercury concentrations in tissues than roe deer in all age groups. Cadmium and mercury concentrations in both species from lowland Croatia are comparable to those given in similar studies in other European countries, while lead concentration was lower in wild boar and higher in roe deer tissues than those in the same species from European countries. From the hygienic point of view, the muscle samples from roe deer and wild boar were edible as the concentrations of cadmium and lead did not exceed the values prescribed by the official regulations. However, cadmium concentration in liver exceeded the prescribed values in one fifth of all samples while lead concentrations were lower than the allowed concentrations. Most kidney samples from both animal species contained cadmium exceeding the recommended concentrations, while lead concentrations in all samples did not exceed the official value regulation. Mercury concentrations are no longer (since 2008) a matter of legislative.

Mercury concentration in ecosystem components in water bodies and streams in Khanh Hoa province (Central Vietnam)

Total mercury concentration in water, seston, soils, and muscle tissues of fish in water bodies in Khan Hoa province was determined. Hg concentration in water does not exceed 40 ng/l. It migrates in water mostly in dissolved form. Hg concentration in soils of the examined water bodies varies from 0.01 to 0.05 mg/(kg dry mass) and that in the muscle tissues of fish on the average does not exceed 1.4 mg/(kg dry mass).

Estimation of mercury uptake efficiency and the development of feed input models for the evaluation of baitfish regimes in determining mercury concentration of farmed southern bluefin tuna ( Thunnus maccoyii)

A model is presented for the prediction of mercury (Hg) concentrations in the edible tissues of farmed southern bluefin tuna, Thunnus maccoyii (SBT) during commercial culture. The predictive model was developed using the initial Hg concentration of wild-caught SBT (mg kg − 1 ), Hg concentration of feed (mg kg − 1 ), SBT feeding rate (kg kg − 1 day − 1 ), SBT tissue growth rate (kg day − 1 ) and least squares minimisation estimation of Hg uptake efficiency, η. Model development and validation was based on experimental data collected from commercially cultured SBT which are farmed in in-sea pontoons (sea-pontoons). Model predictions indicate that over a typical farming season SBT from each of three commercially operated sea-pontoons experienced a 0.1 mg kg − 1 , 0.14 mg kg − 1 and > 0.2 mg kg − 1 reduction in the Hg concentration of muscular tissues respectively. This is the first study to attempt to estimate Hg uptake efficiency in a tuna species. Estimation of Hg uptake efficiency and development of a working model for prediction of Hg concentration in SBT under varying culture diets, represent the first steps towards taking the guesswork out of managing Hg residues in cultured tuna.

Total mercury distribution in different tissues of six species of freshwater fish from the Kpong hydroelectric reservoir in Ghana

Total mercury concentrations were determined in seven tissues of 38 fish samples comprising six species from the Kpong hydroelectric reservoir in Ghana by cold vapour atomic absorption spectrometry technique using an automatic mercury analyzer. Mercury concentration in all the tissues ranged from 0.005 to 0.022μg/g wet weight. In general, the concentration of mercury in all the tissues were decreasing in the order; liver > muscle > intestine > stomach > gonad > gill > swim bladder. Mercury concentration was generally greater in the tissues of high-trophic-level fish such as Clarotes laticeps, Mormyrops anguilloides and Chrysichthys aurutus whereas low-trophic-level fish such as Oreochromis niloticus recorded low mercury concentration in their tissues. The results obtained for total mercury concentration in the muscle tissues analysed in this study are below the WHO/FAO threshold limit of 0.5μg/g. This suggests that the exposure of the general public to Hg through fish consumption can be considered negligible.

Interrelationships between Fish Tissue Mercury Concentrations and Water Quality for South Dakota Natural Lakes and Impoundments

The purpose of this study was to determine whether water quality parameters commonly associated with primary productivity may be used to predict the susceptibility of a specific water body to exceed proposed fish consumption advisory limitation of 0.3 mg kg−1. South Dakota currently has nine lakes and impoundments that exceed fish tissue mercury advisory limits of 1.0 mg kg−1 total mercury, far exceeding US Environmental Protection Agency and Food and Drug Administration 0.3 mg kg−1 consumption criteria. Previous studies suggest that increased aquatic productivity may mitigate the effects of biological production and subsequent uptake of methyl mercury through bio-dilution; however, it is uncertain whether these trends may exist within highly alkaline and highly productive aquatic conditions common to South Dakota lakes and impoundments. Water quality parameters and fish tissue mercury data for northern pike and walleye were collected and assessed using existing South Dakota Department of Environment and Natural Resources and Game Fish and Parks data. The data was initially screened using both parametric linear regression and non-parametric Mann–Whitney rank sum comparisons and further assessed using binary logistic regression and stepwise logistic regression methodology. Three separate phosphorus measurements (total, total dissolved, and Trophic State Index) and pH were determined to significantly correlate with increased mercury concentrations for the northern pike-in-impoundments model. However, phosphorus surprisingly was not a strong predictor for the remaining scenarios modeled. For the northern pike-in-natural lakes models, alkalinity was the most significant water quality parameter predicting increased mercury concentrations. Mercury concentrations for the walleye-in-natural lakes models were further influenced by pH and alkalinity. The water quality and fish tissue mercury interrelationships determined within this study suggest aquatic productivity, and consequential eutrophication processes appear to be reasonable indicators of fish tissue mercury susceptibility for aquatic conditions common to South Dakota and highlight the continuing need to minimize eutrophication through effective watershed management strategies.

Mercury in Liver, Kidney, Feather and Muscle of Seabirds from Major Wetlands of the Caspian Sea, Iran

Concentration of mercury in tissues of the great cormorant (n=18), mallard (n=18), and coot (n=15) of the Caspian Sea were determined. Liver mercury in the great cormorant, mallard, and coot were (5.7±0.91; 0.3±0.02; 0.09±0.02). Kidney levels were (3.6±2.24; 0.26±0.03; 0.08±0.02); feather (8.7±0.8; 1.04±0.16; 0.23±0.15) and muscle were (2.26±2.04; 0.11±0.01; 0.03±0.02) respectively. Mercury Tolerable Daily Intake limit is set at 5μgg(-1). But even at levels that are currently considered "tolerable", mercury poisoning can occur in children and young who consume polluted game meat regularly.

The effects of heavy metals exposure on reproductive systems of cyprinid fish from Kor River

The Kor River (Fars province) was divided into three parts and water and fish specimens were collected monthly and the concentrations of four heavy metals were determined using the Induction Coupled Plasma Method. As middle sampling zone was the main entrance and discharges of industries into the River, the concentrations of heavy metals in tissue of fish from this zone were significantly higher (p 0.05) were detected between the two sexes and species. Maximum concentrations of lead, mercury and cadmium in fish tissues were higher than the permissible levels for human consumption. Significant changes in the concentrations of steroid hormones were also noticed between the middle and two other sampling zones. Also in middle sampling zone, pathological changes in blood cells, liver, and kidneys of fishes were significantly higher. So heavy metals exposure can effectively decrease estrogenic and androgenic secretion in fish. The results confirmed exposure of fishes to heavy metals not only disrupts reproductive hormones’ secretion, but also induces some pathological changes.

Mercury concentrations in oligohaline wetland vegetation and associated soil biogeochemistry

Concentrations of mercury were determined in above- and below-ground tissues of dominant plant species, as well as soils, in the wetlands of Lake Maurepas, Louisiana. Indicators of wetland soil biogeochemical status, such as soil redox potential, pore-water nutrient concentrations, and pore-water total sulfides, were also determined. Total mercury concentrations in plant tissues were within the typical range for vegetation not exposed to mercury contamination. Similarly, total mercury concentrations in soils were typical of uncontaminated wetlands within this geographic region. Soil methyl mercury levels in this study are slightly lower than those reported in other studies of nearby wetlands. This may reflect the less extensive geographic sampling in this study, or the low water levels in the Lake Maurepas system immediately prior to and during this study, which would have altered soil biogeochemical status. This is corroborated by measurements of soil redox potential and soil pore-water nitrogen and sulfur constituents conducted during this study that suggest minimal sulfate reduction was occurring in surficial soils. This study indicates that the wetlands surrounding Lake Maurepas are typical of many uncontaminated oligohaline wetlands in the southeastern U.S. in regard to mercury concentrations.

Stability of Mercury Concentrations in Frozen Avian Blood Samples

It is unclear whether mercury concentration in wildlife tissues changes appreciably after lengthy frozen storage. To test whether such freezer-archived samples are stable, small (~10-50μL) avian blood samples stored in capped glass capillary tubes were analyzed for total mercury concentration, and then reanalyzed after being frozen for up to 3years. Mercury concentrations increased 6% on average over the 3year period, but time spent frozen explained only 11% of the variation between measurements. This small amount of change suggests that archived blood samples remain useful for at least several years.

Ammonium thiosulphate enhanced phytoextraction from mercury contaminated soil – Results from a greenhouse study

According to the ‘hard and soft’ acid-base principle, mercury is a ‘soft metal’ and will preferentially form soluble chemical complexes with sulphur-containing ligands. In this work mercury uptake by Chenopodium glaucum L. growing on mercury-contaminated soil was promoted using ammonium thiosulphate. The relative geochemical fractionation of mercury in the soil was subsequently investigated as a function of plant growth with and without thiosulphate amendment. The results indicate that the solubility of mercury is significantly increased through the application of thiosulphate to the soil. Substantially higher mercury levels were found in C. glaucum L. treated with 2gkg−1 thiosulphate of soil when compared to the non-treated plants. Compared with initial soil, soluble and exchangeable fractions were increased both in planted and planted treated plants. However, no significant difference was observed between the soils of the planted and planted treated plants. The oxide-bound mercury concentration was significantly decreased for the planted soil (treated and non-treated) at the end of the experiment. Moreover, this fraction was highly correlated with the plant tissue mercury concentration. Taken together, thiosulphate assisted phytoextraction could be used to reduce environmental risk apparent for mercury-contaminated soil through reducing the oxide bound fractions, while managing the bioavailable fractions (compared with no treated plant).

Does proximity to coal-fired power plants influence fish tissue mercury?

Much of the mercury contamination in aquatic biota originates from coal-fired power plants, point sources that release mercury into the atmosphere. Understanding mercury dynamics is primarily important because of the toxic threat mercury poses to wildlife and humans through the consumption of contaminated fish. In this study, we quantified the relative importance of proximity to coal-fired power plants on mercury accumulation in two fish species of different trophic positions. Fish, water and sediment were collected and analyzed from 14 lakes, seven near to (<10 km) and seven far from (>30 km) coal-fired power plants. Lower tissue mercury and higher tissue selenium concentrations were measured in fish collected near power plants. Moreover, mercury accumulation in fish was driven by biotic characteristics (e.g., trophic position, total length, age), waterbody characteristics (e.g., pH, dissolved organic carbon and sulfate) and distance from power plants. Proximity to an atmospheric point-source of mercury and selenium, such as a coal-fired power plant, affects the quantities of mercury and selenium accumulated in fish tissue. Differences in accumulation are hypothesized to be driven in part by selenium-mitigated reductions in fish tissue mercury near power plants. Although reduced fish tissue mercury in systems near power plants may decrease mercury-specific risks to human consumers, these benefits are highly localized and the relatively high selenium associated with these tissues may compromise ecological health.

Growth Response and Tissue Accumulation Trends of Herbaceous Wetland Plant Species Exposed to Elevated Aqueous Mercury Levels

The impacts of elevated aqueous mercury levels (0, 2, and 4 ppm) on the growth status and mercury tissue concentrations of Eleocharis parvula, Saururus cernuus, Juncus effuses, Typha latifolia, and Panicum hemitomon were determined. Both short-term (net CO2 assimilation) and long-term (biomass) indicators of plant growth status suggest that Eleocharis parvula, Saururus cernuus, and Juncus effuses were relatively unimpacted by elevated mercury levels, whereas Typha latifolia and Panicum hemitomon were somewhat impacted at elevated mercury levels. Eleocharis parvula, Panicum hemitomon, and Typha latifolia generally had the greatest overall belowground tissue concentrations of mercury (2 ppm treatment: 7.21, 7.32, and 9.64 ppm respectively; 4 ppm treatment: 16.23, 18.23, and 13.98 ppm, respectively) and aboveground tissue concentrations of mercury (2 ppm treatment: 0.01, 0.04, 0.02; 4 ppm treatment: 0.26; 0.11; 0.17 ppm, respectively). However, the species investigated in this study demonstrated lower levels of mercury accumulation into tissues when compared with similar investigations of other aquatic plants, suggesting that the above species are not optimal for phytoremediation efforts.

Mercury Concentrations in Largemouth Bass (Micropterus salmoides) Collected from Ash Meadows National Wildlife Refuge, Nye County, Nevada

Mercury is a known neurotoxin and contaminant of concern worldwide. Mercury may occur at elevated concentrations adjacent to industrial sources, such as coal-fired power plants, or in remote environments and newly filled water bodies. Mercury tissue concentrations were determined for a sample of largemouth bass (Micropterus salmoides) from Crystal Reservoir, Ash Meadows National Wildlife Refuge, Nye County, Nevada. This investigation was triggered by (1) the presence of several conditions in soil and water that facilitate mercury bioaccumulation, (2) previous investigations that detected mercury in source springs, and (3) the presence of game fish and endangered pupfish within the reservoir. Mercury concentrations were significantly correlated with both fish mass and condition, but were lower than national human health and safety standards. It is possible that high pH and salinity inhibited methylation and subsequent bioaccumulation; however, additional studies are needed to determine causation of the low concentration in fish tissue compared with ambient conditions.

Tissue mercury concentrations and adrenocortical responses of female big brown bats (Eptesicus fuscus) near a contaminated river

Much of the research on mercury (Hg) in wild vertebrates has focused on piscivores and other animals at high trophic levels. However, recent studies indicated that insectivorous terrestrial vertebrates may also be at risk. In the present study, we examined blood and fur Hg concentrations as well as the adrenocortical responses of insectivorous big brown bats (Eptesicus fuscus) near the Hg-contaminated South River, VA and a nearby reference area. Baseline glucocorticoids and adrenocortical responses to handling have been widely used to assess the influence of environmental stressors because plasma glucocorticoids rise in response to various physical, psychological, and physiological challenges. Female bats captured at the contaminated site had 2.6 times higher blood and fur Hg concentrations than those captured at the reference site (blood: 0.11 vs. 0.04 μg/g wet weight; fur: 28.0 vs. 10.9 μg/g fresh weight). Fur Hg concentrations at the contaminated site were higher than most wild omnivorous and carnivorous mammals reported in the literature. Although fur and blood Hg concentrations were tightly correlated, fur Hg concentrations averaged 260 times higher than concentrations in blood. This suggests that fur may be an important depuration route for bats, just as it is in other mammals. Despite the high Hg concentrations in bat tissue, we did not observe any site difference in adrenocortical responses. Our results suggest that the bats at the contaminated site were exposed to Hg concentrations below those causing adverse effects on their adrenal axis.