Mercury In Fish Tissue Research Articles

Robust ultrasound assisted extraction approach using dilute TMAH solutions for the speciation of mercury in fish and plant materials by cold vapour atomic absorption spectrometry (CVAAS)

A simple and robust ultrasound assisted extraction (UAE) protocol with dilute solutions of tetramethyl ammonium hydroxide (TMAH) for the speciation of mercury in fish and plant tissues was developed by CVAAS as an alternative to conventional methods.

A national statistical survey assessment of mercury concentrations in fillets of fish collected in the U.S. EPA national rivers and streams assessment of the continental USA

The U.S. EPA conducted a national statistical survey of fish fillet tissue with a sample size of 541 sites on boatable rivers =>5th order in 2008–2009. This is the first such study of mercury (Hg) in fish tissue from river sites focused on potential impacts to human health from fish consumption to also address wildlife impacts. Sample sites were identified as being urban or non-urban. All sample mercury concentrations were above the 3.33ugkg−1 (ppb) quantitation limit, and an estimated 25.4% (±4.4%) of the 51663 river miles assessed exceeded the U.S. EPA 300ugkg−1 fish-tissue based water quality criterion for mercury, representing 13144±181.8 river miles. Estimates of river miles exceeding comparable aquatic life thresholds (translated from fillet concentrations to whole fish equivalents) in avian species were similar to the number of river miles exceeding the human health threshold, whereas some mammalian species were more at risk than human from lower mercury concentrations. A comparison of means from the non-urban and urban data and among three ecoregions did not indicate a statistically significant difference in fish tissue Hg concentrations at p<0.05.

Mercury cycling in aquatic ecosystems and trophic state-related variables — Implications from structural equation modeling

Structural equation modeling (SEM) provides a framework that can more properly handle complex variable interactions inherent in mercury cycling and its bioaccumulation compared to more traditional regression-based methods. SEM was applied to regional data sets for three different types of aquatic ecosystems within Florida, USA – lakes, streams, and the Everglades – to evaluate the underlying nature (i.e., indirect and direct) of the relationships between fish mercury concentrations and trophic state related variables such as nutrients, dissolved organic carbon (DOC), sulfate, and alkalinity. The modeling results indicated some differences in key variable relationships — for example, the effect of nutrients on fish mercury in lakes and streams was uniformly negative through direct and indirect pathways consistent with biodilution or eutrophication-associated effects on food web structure. Somewhat surprisingly, however, was that total phosphorus did not serve as a meaningful variable in the Everglades model, apparently because its effects were masked or secondary to the effects of DOC. What is perhaps a more important result were two key similarities across the three systems. First, the modeling clearly indicates that the dominant influence on fish tissue mercury concentrations in all three systems is related to variations in the methylmercury signal. Second, the modeling demonstrated that the effect of DOC on fish mercury concentrations was exerted through multiple and antagonistic pathways, including facilitated transport of total mercury and methylmercury, enhanced rates of methylation, and limitations imposed on bioavailability. Indeed, while the individual DOC pathways in the models were all highly significant (generally p<0.001), the net effect of DOC in each model was greatly reduced or insignificant. These results can help explain contradictory results obtained previously by other researchers in other systems, and illustrate the importance of SEM as a modeling tool when studying systems with complex interactions such as the aquatic mercury cycle.

Determination of Total Mercury in Fish Tissue Using a Low-Cost Cold Vapor Capacitively Coupled Plasma Microtorch Optical Emission Microspectrometer: Comparison with Direct Mercury Determination by Thermal Decomposition Atomic Absorption Spectrometry

A method for total Hg determination in fish tissue using cold vapor capacitively coupled plasma microtorch optical emission spectrometry was evaluated. The low-cost miniaturized analytical system includes a low power plasma microtorch (10 W) and low Ar consumption (150 ml min−1) and a QE65Pro microspectrometer as detector. Lyophilized fish tissues were microwave-assisted digested in HNO3–H2O2 mixture, brought in 5 % (v/v) HCl, then Hg vapor was chemically generated with 20 % SnCl2 solution stabilized in 15 % (v/v) HCl. The figures of merit of the proposed method were evaluated by analyzing certified reference materials and test samples and compared to those of the well-established thermal decomposition atomic absorption spectrometry method. The analytical characteristics (limits of detection and quantification, precision, and accuracy) comply with requirements for Hg determination in seafood set out in Decisions 2007/333/EC and 2002/657/EC. The limits of detection and quantification of the proposed method were 3 and 9 μg kg−1 Hg in dry mass, similar to those in thermal decomposition atomic absorption spectrometry. The precision was between 1.8 and 5.5 % for concentrations in the range 0.18–0.76 mg kg−1 Hg, while the accuracy was 99.7 ± 3.0 %. The significance tests revealed no difference between the results obtained by the two methods. The proposed miniaturized spectrometric equipment could be the subject of prototyping as low-cost instrumentation for designed applications in seafood control.

Response of fish tissue mercury in a freshwater lake to local, regional, and global changes in mercury emissions.

A suite of mechanistic atmospheric and mercury (Hg) cycling and bioaccumulation models is applied to simulate atmospheric Hg deposition and Hg concentrations in the water column and in fish in a Hg-impaired freshwater lake located in the northeastern United States that receives its Hg loading primarily through deposition. Two future-year scenarios evaluate the long-term response of fish tissue Hg concentrations to reductions in local and nationwide coal-fired electric-generating utility and other Hg emissions and an increase or decrease in global (non-US) Hg emissions. Results indicate that fish tissue Hg concentrations in this ecosystem could require approximately 3 yr to 8 yr to begin to respond to declines in US emissions and deposition with a fish Hg reduction proportional to deposition reduction requiring over 50 yr. Furthermore, recovery could potentially be partially or completely offset by growth in non-US Hg emissions.

Trends in blood mercury concentrations and fish consumption among U.S. women of reproductive age, NHANES, 1999–2010

BackgroundConsumption of finfish and shellfish is the primary exposure pathway of methylmercury (MeHg) in the US. MeHg exposure in utero is associated with neurodevelopmental and motor function deficits. Regulations and fish advisories may contribute to decreased exposure to mercury over time. ObjectivesCombine fish tissue mercury (FTHg) concentrations and 1999–2010 NHANES blood mercury concentrations and fish consumption data to investigate trends in blood mercury concentrations, fish consumption, and mercury intake in women of reproductive age. MethodsBlood MeHg was calculated from the blood total and inorganic concentrations. Dietary datasets were combined to estimate 30-day fish consumption, then combined with FTHg concentrations to estimate mercury intake and mercury concentration in the fish consumed. Non-linear and logistic regression analyses were used to evaluate trends over time. ResultsRegression analysis found NHANES 1999–2000 to have higher blood MeHg concentrations than the mean of the later releases (p<0.0001) and a positive quadratic trend since 2000 (p=0.004). No trend was observed in fish consumption amount or mercury intake. A decreasing trend was found in the ratio of mercury intake to fish consumed (p=0.04). ConclusionsThe analyses found blood MeHg concentrations in NHANES 1999–2000 to be significantly higher than the mean of the later releases. There was no trend in fish consumption amount across the study period. The analysis found a decreasing trend in the ratio of mercury intake to fish consumed, consistent with women shifting their consumption to fish with lower mercury concentrations.

Temporal and Spatial Trends in Freshwater Fish Tissue Mercury Concentrations Associated with Mercury Emissions Reductions

Mercury (Hg) concentrations were monitored from 1999 to 2011 in largemouth bass (LMB) and yellow perch (YP) in 23 lakes in Massachusetts USA during a period of significant local and regional Hg emissions reductions. Average LMB tissue Hg concentration decreases of 44% were seen in 13 of 16 lakes in a regional Hg "hotspot" area. YP in all lakes sampled in this area decreased 43% after the major emissions reductions. Comparative decreases throughout the remainder of the state were 13% and 19% for LMB and YP respectively. Annual tissue mercury concentration rate decreases were 0.029 (LMB) and 0.016 mg Hg/kg/yr (YP) in the hotspot. In lakes around the rest of the state, LMB showed no trend and YP Hg decreased 0.0068 mg Hg/kg/yr. Mercury emissions from major point sources in the hotspot area decreased 98%, and 93% in the rest of the state from the early 1990s to 2008. The significant declines in fish Hg concentrations in many lakes occurred over the second half of a two decade decrease in Hg emissions primarily from municipal solid waste combustors and, secondarily, from other combustion point sources. In addition to the substantial Hg emissions reductions achieved in Massachusetts, further regional, national and global emissions reductions are needed for fish Hg levels to decrease below fish consumption advisory levels.

Anatomical mercury speciation in bay scallops by thio-bearing chelating resin concentration and GC-electron capture detector determination

The highly toxic methyl-, ethyl- and phenylmercury species that may exist in the three main anatomical parts – the adductor muscle, the mantle and the visceral mass – of bay scallops (Argopecten irradias) were quantitatively released by cupric chloride, zinc acetate, sodium chloride and hydrochloric acid (HCl) under ultrasonic extraction. After centrifugation, the mercury species in the supernatant were concentrated by thio (SH)-bearing chelating resins, eluted with HClO4 and HCl and extracted with toluene. Separation was achieved by capillary GC equipped with programmed temperatures, a constant nitrogen flow and detected by a micro-electron capture detector (μECD). Under optimised conditions, the LODs for methyl-, ethyl- and phenylmercury in bay scallop samples were 1.1, 0.65 and 0.80 ng g−1, respectively. The maximum RSD for three replicate determinations of methyl-, ethyl- and phenylmercury in bay scallop samples were 13.7%, 14.0% and 11.2%, respectively. In the concentration range of 4–200 ng g−1 in bay scallop samples, the calibration graphs were linear with correlation coefficients not less than 0.997. Recoveries for spiked samples were in the range of 92.7–103.5% (methylmercury), 87.5–108.3% (ethylmercury) and 91.6–106.0% (phenylmercury), respectively. The method was verified by the determination of methylmercury in a CRM GBW10029 (Total Mercury and Methyl Mercury in Fish Tissue), with results in good agreement with the certified values. Methylmercury – the only existing species in bay scallops – was successfully determined by the method.

A Methylmercury Risk Screening Assessment to Identify Fish Species and Populations of Potential Concern

State fish consumption advisories provide meal limit recommendations for recreationally-caught fish. In Louisiana, these recommendations are based on species-specific fish tissue contaminant concentrations, and default assumptions about fish consumption. This approach can lead to advisories for infrequently eaten species, and inappropriately targeted monitoring and outreach activities. The goal of this study is to identify and prioritize species, populations and areas of potential concern based on a screen of mercury intake. Mercury doses were estimated based on species-specific fish consumption data from a population-based survey of Louisiana's recreational fishers (n=1774), and regional fish tissue mercury concentration data (n=15,030). Estimates of species-specific mercury doses were derived for each survey respondent based on mean and 90 th percentile fish tissue mercury levels. Mercury exposure distributions for various species and sub-populations were compared to the U.S. Environmental Protection Agency's health-based standard for methyl-mercury. As children and commercial and subsistence fishers were not surveyed, conclusions presented here are only applicable to adult recreational fishers, who are expected to eat less fish than commercial and subsistence fishers. Species with the largest number of at-risk fishers were drum (primarily red drum), speckled trout, catfish, crappie, bass and bream. Populations of potential concern included women of childbearing age; African- and Native-Americans; fishers from northern Louisiana; and fishers with Hook and Line and Basic licenses. Results were used to make recommendations to optimize monitoring, advisory development and outreach activities. This study demonstrates the importance of collecting fish consumption data for ensuring adequate public health protection.

Cardiorespiratory responses to graded hypoxia in the neotropical fish matrinxã (Brycon amazonicus) and traíra (Hoplias malabaricus) after waterborne or trophic exposure to inorganic mercury

The growing Hg input in aquatic environments results in high accumulation of mercury in fish tissue and their consumers, which poses a serious risk to humans and ecosystems. The aim of this study was to evaluate the effects of the inorganic mercury exposure on cardiorespiratory responses in two species of neotropical fish ecologically distinct, matrinxã (Brycon amazonicus) and traíra (Hoplias malabaricus). Matrinxãs were exposed to a nominal and sublethal concentration of 0.15mgL−1 of HgCl2 for 96h. Traíras were exposed to trophic doses (each 4 days, during 30 days) of inorganic Hg (0.45mg as total Hg) using juvenile B. amazonicus as prey vehicle. The metabolic rate (V˙O2), critical oxygen tensions (PcO2), gill ventilation (V˙G), tidal volume (VT), respiratory frequency (fR), O2 extraction from the ventilatory current (EO2), and heart rate (fH) were measured under normoxia (140mmHg) and graded hypoxia (120, 100, 80, 60, 40, 20, and 10mmHg). Regarding matrinxã specifically, the critical point highlighted was tachypnea. In traíras, bradypnea, decreased metabolic rate and O2 extraction, severe bradycardia, and elevated tidal volume were observed in normoxia. Both acute and sub-chronic exposures increased the critical tension of O2 values in more than 100%. In addition, Hg exposures modulated hypoxia-induced responses resulting in impairment of cardio-respiratory system of both species. Thus, mercury, via food or water, decreases the plasticity of the cardiorespiratory responses reducing the survival chances of B. amazonicus and H. malabaricus under hypoxic conditions frequently observed in theirs wild habitats.

Short-term impact of reservoir impoundment on the patterns of mercury distribution in a subtropical aquatic ecosystem, Wujiang River, southwest China

Surveys on pre- and post-impoundment total mercury concentrations in water, seston and fish were conducted during 2007-2008 in the Wujiang River, southwest China. Compared with the pre-impoundment, total mercury in the reservoir and downstream water rapidly increased by 164-303% during the first half year of flooding, and then decreased by 61.7-62.2% after 9months of flooding. However, total mercury in seston from the reservoir and downstream generally declined. There was no significant difference in the total mercury between reservoir fish with different habitat preference and feeding habit. We find that fish tissue mercury concentration significantly increased threefold after flooding, and the increasing rate is lower than those in subarctic and temperate reservoirs. The pre- and post-impoundment fish samples exceeding the Chinese hygienic standard for tolerances of mercury in foods increased from 1.3 to 17.4%. Long-term monitoring of fish mercury level in Wujiang River should be undertaken to ensure local food security.

Validation of a Predictive Model for Fish Tissue Mercury Concentrations

AbstractIn an effort to reconcile the extensive variability in fish tissue mercury (Hg) in North Carolina, we previously created a predictive model using data collected from 1990 to 2006. Our model identified four factors—fish trophic status, fish species, ecoregion, and water pH—that explained 81% of the variation in fish tissue Hg. Herein, we evaluate the performance of this model by using two independently collected data sets describing fish tissue Hg in North Carolina and Virginia. Our model explained 75% of the variation in independently collected tissue Hg data from North Carolina and 68% of the variation in data collected from the same ecoregion types in Virginia. Although the relationships were relatively strong, the model generally underestimated observed tissue Hg. Residual analysis indicated that at least some of the model bias was due to error in predictions for sites near (within 10 km of) coal‐fired power plants. The model was not significantly biased when sites near power plants were removed from the independent data set, suggesting that the model was best at predicting mean tissue Hg in adult fish collected from water bodies greater than 10 km from power plants; such sites constitute the majority of the landscape. Fortuitously, fish at sites near power plants have significantly less tissue Hg than fish at sites far from power plants and are therefore of less concern to public health officials. The validated model can serve as a fish tissue Hg screening tool for use by state and federal agencies because it was created to predict Hg levels in numerous species and systems, and it only requires data that are readily available or relatively simple and inexpensive to measure. Identification of specific systems that may have highly contaminated fish and would not otherwise be sampled due to limited resources will help to focus sampling and enhance efforts to protect fish consumers.

Regional variation in mercury and stable isotopes of red snapper (Lutjanus campechanus) in the northern gulf of Mexico, USA

The presence of total mercury (Hg) in fish tissue and the potential associated health risks has become a global concern in marine ecosystems. Few studies have examined basin-scale variation in Hg accumulation in marine ecosystems, and determining if Hg concentrations in fish tissue vary across marine ecosystems is a key monitoring question. The present study evaluated Hg concentrations in red snapper (Lutjanus campechanus) tissue across three regions of the northern Gulf of Mexico (Alabama, Louisiana, and Texas, USA) and between two habitat types (oil and gas platforms and nonplatforms) within each region. Nitrogen (δ(15)N), carbon (δ(13)C), and sulfur (δ(34)S) stable isotopes were used to investigate ecological differences that may affect Hg concentrations among regions and between habitats. Mercury concentrations in red snapper tissue were positively correlated with fish total length. Regional differences in Hg concentrations were significant, with fish collected from Alabama having the highest concentrations and fish collected from Louisiana having the lowest. No significant difference existed in Hg concentrations between habitats, suggesting that association with platforms may not be a significant factor contributing to red snapper Hg concentrations. While δ(15)N did not differ significantly among the three regions, Texas red snapper were more enriched in δ(34)S and depleted in δ(13)C compared with Alabama and Louisiana red snapper. Although the majority of red snapper collected in the present study had Hg concentrations below safe consumption guidelines, regional differences suggest that spatially explicit monitoring programs may be important for basin-wide assessments.

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.

Distribution and chemical form of mercury in commercial fish tissues

We analyzed total Hg concentrations in various tissue samples obtained from 7 commercially available fish species. MeHg contents were also estimated for muscle and liver samples by a selective analysis of inorganic Hg. Among the tissues, high Hg accumulations were shown in liver, muscle, heart and spleen throughout all fish species. Carnivorous fish, such as scorpion fish, sea bream and Japanese whiting, tended to show higher Hg accumulations in the muscle, with the highest Hg levels being shown by scorpion fish. Although the liver was expected to show the highest Hg accumulations among tissues throughout all fish species, the highest accumulation in the liver was observed only in scorpion fish. In contrast, the muscle level was significantly higher than the liver in Pacific saury and Japanese whiting. MeHg accumulated in fish is considered to show a sustained increase throughout the life of the fish, due to its long biological half-life. In fact, in the present study, muscle Hg levels in Japanese whiting, Japanese flying fish, and halfbeak showed good correlations with body weights. However, such correlations were not clear in scorpion fish, sea bream, Jack mackerel and Pacific saury. Selective analyses of inorganic Hg levels revealed that most of the Hg (> 95%) in fish muscle existed as MeHg, while the rates of MeHg contents in the liver varied from 56% in scorpion fish to 84% in Jack mackerel. As a result, fish muscle showed the highest MeHg accumulations in all fish species examined. These results suggest that reliable information on total Hg contents in fish muscle might be sufficient to avoid the risk of MeHg exposure caused by eating fish, even when one consumes other tissues such as fish liver.

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.

Using River Distance and Existing Hydrography Data Can Improve the Geostatistical Estimation of Fish Tissue Mercury at Unsampled Locations

Mercury in fish tissue is a major human health concern. Consumption of mercury-contaminated fish poses risks to the general population, including potentially serious developmental defects and neurological damage in young children. Therefore, it is important to accurately identify areas that have the potential for high levels of bioaccumulated mercury. However, due to time and resource constraints, it is difficult to adequately assess fish tissue mercury on a basin wide scale. We hypothesized that, given the nature of fish movement along streams, an analytical approach that takes into account distance traveled along these streams would improve the estimation accuracy for fish tissue mercury in unsampled streams. Therefore, we used a river-based Bayesian Maximum Entropy framework (river-BME) for modern space/time geostatistics to estimate fish tissue mercury at unsampled locations in the Cape Fear and Lumber Basins in eastern North Carolina. We also compared the space/time geostatistical estimation using river-BME to the more traditional Euclidean-based BME approach, with and without the inclusion of a secondary variable. Results showed that this river-based approach reduced the estimation error of fish tissue mercury by more than 13% and that the median estimate of fish tissue mercury exceeded the EPA action level of 0.3 ppm in more than 90% of river miles for the study domain.

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.

Measurement of methyl mercury (I) and mercury (II) in fish tissues and sediments by HPLC-ICPMS and HPLC-HGAAS

A procedure for the extraction and determination of methyl mercury and mercury (II) in fish muscle tissues and sediment samples is presented. The procedure involves extraction with 5% (v/v) 2-mercaptoethanol, separation and determination of mercury species by HPLC-ICPMS using a Perkin-Elmer 3μm C8 (33mm×3mm) column and a mobile phase 3 containing 0.5% (v/v) 2-mercaptoethanol and 5% (v/v) CH3OH (pH 5.5) at a flow rate 1.5mlmin−1 and a temperature of 25°C. Calibration curves for methyl mercury (I) and mercury (II) standards were linear in the range of 0–100μgl−1 (r2=0.9990 and r2=0.9995 respectively). The lowest measurable mercury was 0.4μgl−1 which corresponds to 0.01μgg−1 in fish tissues and sediments. Methyl mercury concentrations measured in biological certified reference materials, NRCC DORM – 2 Dogfish muscle (4.4±0.8μgg−1), NRCC Dolt – 3 Dogfish liver (1.55±0.09μgg−1), NIST RM 50 Albacore Tuna (0.89±0.08μgg−1) and IRMM IMEP-20 Tuna fish (3.6±0.6μgg−1) were in agreement with the certified value (4.47±0.32μgg−1, 1.59±0.12μgg−1, 0.87±0.03μgg−1, 4.24±0.27μgg−1 respectively). For the sediment reference material ERM CC 580, a methyl mercury concentration of 0.070±0.002μgg−1 was measured which corresponds to an extraction efficiency of 92±3% of certified values (0.076±0.04μgg−1) but within the range of published values (0.040–0.084μgg−1; mean±s.d.: 0.073±0.05μgg−1, n=40) for this material. The extraction procedure for the fish tissues was also compared against an enzymatic extraction using Protease type XIV that has been previously published and similar results were obtained. The use of HPLC-HGAAS with a Phenomenox 5μm Luna C18 (250mm×4.6mm) column and a mobile phase containing 0.06moll−1 ammonium acetate (Merck Pty Limited, Australia) in 5% (v/v) methanol and 0.1% (w/v) l-cysteine at 25°C was evaluated as a complementary alternative to HPLC-ICPMS for the measurement of mercury species in fish tissues. The lowest measurable mercury concentration was 2μgl−1 and this corresponds to 0.1μgg−1 in fish tissues. Analysis of enzymatic extracts analysed by HPLC-HGAAS and HPLC-ICPMS gave equivalent results.

Development of an Empirical Nonlinear Model for Mercury Bioaccumulation in the South and South Fork Shenandoah Rivers of Virginia

Mercury is a globally distributed pollutant that biomagnifies in aquatic food webs. In the United States, 3781 water bodies fail to meet criteria for safe fish consumption due to mercury bioaccumulation. In the risk assessment and management of these impairments (through the total maximum daily load program), an important step is evaluating the relationship between aqueous mercury and mercury in fish tissue. Often, this relationship is simplified to a bioaccumulation factor (BAF): the ratio of fish tissue mercury to aqueous mercury. This article evaluates the relationship between aqueous mercury and fish tissue mercury across a contamination gradient in the South and South Fork Shenandoah rivers of Virginia. The relationship was found to be nonlinear, with BAFs decreasing as the level of contamination increased. This means that protective water column mercury concentration targets established from site-specific BAFs will be overestimated in contaminated areas and will not be sufficiently protective. To avoid this over-prediction in the South and South Fork Shenandoah rivers, an empirical nonlinear Michaelis-Menten model was used to establish a protective water-quality target. Among other models and variables, the Michaelis-Menten model, relating total mercury in the water column to methylmercury in fish tissue, achieved the best empirical fit (r(2) = 0.9562). The resulting water-quality targets using this model were 3.8 and 3.2 ng/l for the South and South Fork Shenandoah rivers, respectively. These values are 2.1-2.5 times lower than the water-quality target developed using a site-specific BAF. These findings demonstrate the need to consider nonlinear BAF relationships in mercury-contaminated areas.