Automated simultaneous analysis of monomethyl and mercuric Hg in biotic samples by Hg-thiourea complex liquid chromatography following acidic thiourea leaching

Ultratrace mercury speciation analysis in rice by in-line solid phase extraction - liquid chromatography - atomic fluorescence spectrometry

For the first time, Hg²⁺ and methylmercury speciation analysis was accomplished by in-line SPE-LC-AFS. After modification with 0.1 mL of 0.001% (m:v) sodium diethyldithiocarbamate, a C₁₈ microcolumn retained Hg²⁺ and MetHg in rice extract within 3 min; the captured Hg species were separated within 12 min in 0.25% (v:v) 2-mercaptoethanol + 60 mmol L^-1 (m:v) ammonium acetate + 4% (v:v) acetonitrile. Under optimized conditions, the detection limits were 0.3 ng L^-1 for Hg²⁺ and 0.2 ng L^-1 for MetHg, respectively, with 10 mL injection vs. 0.1 mL eluent; in-line SPE achieved ∼ 100x enrichment. Method precision and accuracy were satisfactory at < 2% relative standard deviations (RSDs) for 20 ng L^-1 of Hg²⁺ and MetHg and 95-102% recoveries for real rice samples. In-line SPE obviated human involvement and avoided invalid transportation between interfaces, rendering this SPE-LC-AFS method easy, compact, robust, yet sensitive in mercury speciation analysis to uphold food safety.

Isotopic and chemical characteristics of mercury in organs and tissues of fish in a mercury-polluted lake: Evidence for fractionation of mercury isotopes by physiological processes

Organs and tissues of whitefish and trout from mercury (Hg)-polluted Lake Ontario were analyzed for Hg isotopes, methylmercury (CH₃ Hg⁺ ), and inorganic Hg to investigate possible mass-dependent fractionation (MDF) and mass-independent fractionation (MIF) of Hg isotopes by physiological processes of the fish. Isotope signatures of different body parts were defined by δ-values of ¹⁹⁸ Hg/²⁰² Hg, ¹⁹⁹ Hg/²⁰² Hg, ²⁰⁰ Hg/²⁰² Hg, and ²⁰¹ Hg/²⁰² Hg ratios and by Δ-values representing effects of MIF on ¹⁹⁹ Hg/²⁰² Hg and ²⁰¹ Hg/²⁰² Hg ratios. The research yielded the following evidence for MDF and MIF, including MIF of isotopes with even as well as odd mass numbers, by metabolic activities: 1) anomalously low δ-values for whitefish kidneys but not for trout kidneys; 2) widely varying differences between the δ-values of different body parts of whitefish but practically uniform differences for those of trout; 3) different relationships between Δ¹⁹⁹ Hg and Δ²⁰¹ Hg for whitefish than for trout; 4) nonlinear correlation between δ¹⁹⁸ Hg and δ²⁰⁰ Hg for whitefish but linear correlation for trout; 5) an inverse correlation between the δ¹⁹⁹ Hg values and CH₃ Hg⁺ concentrations of whitefish and trout; 6) an inverse correlation between the δ²⁰¹ Hg/δ¹⁹⁹ Hg and CH₃ Hg⁺ /inorganic Hg ratios of trout kidneys and gills (and lipids of trout near the sources of pollution) but a positive correlation for muscle, liver, and gut; and 7) inverse correlations between Δ¹⁹⁹ Hg and the CH₃ Hg⁺ /inorganic Hg ratio for trout liver, kidneys, and gut. Environ Toxicol Chem 2018;37:515-529. © 2017 SETAC.

Development of a new diffusive gradient in the thin film (DGT) method for the simultaneous measurement of CH3Hg+ and Hg2+

This technique has a high DGT capacity, wide tolerance of pH and ionic strength and good performance as an in situ monitoring tool.

Changes in Sport Fish Mercury Concentrations from Food Web Shifts Suggest Partial Decoupling from Atmospheric Deposition in Two Colorado Reservoirs

Partial decoupling of mercury (Hg) loading and observed Hg concentrations ([Hg]) in biotic and abiotic samples has been documented in aquatic systems. We studied two Colorado reservoirs to test whether shifts in prey for sport fish would lead to changes in [Hg] independent of external atmospheric Hg deposition. We compared sport fish total mercury concentrations ([T-Hg]) and macroinvertebrate (chironomids and crayfish) methylmercury concentrations ([MeHg]) before and after food web shifts occurred in both reservoirs. We also monitored wet atmospheric Hg deposition and sediment [T-Hg] and [MeHg] at each reservoir. We found rapid shifts in Hg bioaccumulation in each reservoir's sport fish, and these changes could not be attributed to atmospheric Hg deposition. Our study shows that trends in atmospheric deposition, environmental samples (e.g., sediments), and samples of species at the low trophic levels (e.g., chironomids and crayfish) may not accurately reflect conditions that result in fish consumption advisories for high trophic level sport fish. We suggest that in the short-term, monitoring fish [Hg] is necessary to adequately protect human health because natural and anthropogenic perturbations to aquatic food-webs that affect [Hg] in sport fish will continue regardless of trends in atmospheric deposition.

Effects of prey assemblage on mercury bioaccumulation in a piscivorous sport fish

Mercury (Hg) is a persistent global contaminant that biomagnifies, often reaching maximum levels in apex predators. Mercury contamination in piscivorous fish is a serious health risk for anglers and other fish consumers. We used data collected from a reservoir in Colorado to develop bioenergetics-based simulations of Hg bioaccumulation to estimate Hg concentrations in walleye (Sander vitreus), a popular sport fish. We evaluated how changes in the prey available to walleye might affect walleye Hg concentrations. Our simulations showed that such changes could result in almost a 10-fold range in walleye Hg concentration. Walleye consuming invertebrates had low growth, low growth efficiency, and high Hg concentrations. Conversely, when walleye diet contained only fish prey their growth and growth efficiency were higher and Hg concentrations were about 85% lower. These predictions were consistent with independent measurements in the study system observed under two different prey regimes in 2008 and 2013. Because prey assemblages in freshwaters can exhibit high natural and anthropogenic variability, understanding variation in predator Hg and providing accurate fish consumption advice to anglers and their families will require frequent monitoring of both predator and prey species. Further, manipulation of prey assemblages is a routine fishery management strategy that could be applied to reduce Hg contamination in piscivorous fishes.

Determination of mercury speciation in fish tissue with a direct mercury analyzer

Knowledge of Hg speciation in tissue is valuable for assessing potential toxicological effects in fish. Direct Hg analyzers, which use thermal decomposition and atomic absorption spectrometry, have recently gained popularity for determining organic Hg after procedural solvent extraction from some environmental media, although quantitative recovery from lipid-rich materials, such as fish liver, has been problematic. The authors developed a new method by which organic Hg in fish liver and muscle is estimated by the difference between direct measurements of inorganic Hg in an acid extract and total Hg in whole tissue. The method was validated by analysis of a certified reference material (DOLT-4 dogfish liver) and naturally contaminated fish tissues with comparison to an established Hg speciation method (gas chromatography cold vapor atomic fluorescence spectrometry). Recovery of organic Hg from DOLT-4, estimated by difference, averaged 99 ± 5% of the mean certified value for methylmercury. In most liver samples and all muscle samples, estimates of organic Hg from the proposed method were indiscernible from direct speciation measurements of methylmercury (99% ± 6%). Estimation of organic Hg by the difference between total Hg and inorganic Hg was less accurate in liver samples with a high percentage of inorganic Hg (90%). This was because of the increased uncertainty that results from estimating a third value (i.e., organic Hg) by using the difference between two large concentrations (inorganic and total Hg). The proposed method is a useful tool for examining the speciation of Hg in fish muscle and liver, and by extension, potentially other tissues and environmental media.

Mercury exposure is associated with negative effects on turtle reproduction

Mercury (Hg), a ubiquitous and highly toxic bioaccumulative contaminant, can maternally transfer and elicit deleterious effects on adult reproduction and offspring phenotype in fish, amphibians, and birds. However, the effects of Hg on reproduction remain largely unstudied in reptiles. We evaluated the consequences of maternally transferred Hg on a long-lived aquatic omnivore, the common snapping turtle (Chelydra serpentina). We collected eggs and tissues from gravid female turtles along a broad Hg contamination gradient in a river in central Virginia. We incubated eggs in the laboratory, quantified embryonic mortality, infertility, and hatching success of each clutch, and assessed all hatchlings and dead embryos for gross morphological malformations. As predicted, Hg concentrations in eggs were strongly and positively correlated with Hg levels in female tissues. We found that Hg in eggs was negatively correlated with hatching success, and this effect was driven by both increased egg infertility and embryonic mortality. In comparison to previous effect-based studies on other amniotes, our findings suggest that C. serpentina may be more resilient to Hg exposure and perhaps better suited for long-term monitoring of bioavailability of Hg than as indicators of adverse effects.

The influence of external subsidies on diet, growth and Hg concentrations of freshwater sport fish: implications for management and fish consumption advisories

Mercury (Hg) contamination in sport fish is a global problem. In freshwater systems, food web structure, sport fish sex, size, diet and growth rates influence Hg bioaccumulation. Fish stocking is a common management practice worldwide that can introduce external energy and contaminants into freshwater systems. Thus, stocking can alter many of the factors that influence Hg concentrations in sport fish. Here we evaluated the influence of external subsidies, in the form of hatchery-raised rainbow trout Oncorhynchus mykiss on walleye Sander vitreus diet, growth and Hg concentrations in two freshwater systems. Stocking differentially influenced male and female walleye diets and growth, producing a counterintuitive size-contamination relationship. Modeling indicated that walleye growth rate and diet were important explanatory variables when predicting Hg concentrations. Thus, hatchery contributions to freshwater systems in the form of energy and contaminants can influence diet, growth and Hg concentrations in sport fish. Given the extensive scale of fish stocking, and the known health risks associated with Hg contamination, this represents a significant issue for managers monitoring and manipulating freshwater food web structures, and policy makers attempting to develop fish consumption advisories to protect human health in stocked systems.

Methylmercury concentrations in six fish species from two Colombian rivers

The objective of this study was to determine whether fish collected from the La Miel or Nechí Rivers (Colombia) differed in muscle methyl mercury (meHg) concentration. Two fish from six different species were collected from markets adjacent to each river. Overall, fish collected from the market adjacent to the Nechí River contained higher levels of meHg. This result however is being driven by very high meHg concentrations in four individual fish, three of which are Pimelodid, long-whiskered catfish. These catfish may represent ideal sentinel organism for the detection of meHg contamination in Colombian rivers.

Assessment of mercury and selenium concentrations in captive bottlenose dolphin's (Tursiops truncatus) diet fish, blood, and tissue

Concentrations of total mercury (Hg) and selenium (Se) were determined in diet fish and whole blood and tissue samples from seven bottlenose dolphins (Tursiops truncatus) housed at the National Aquarium Baltimore (NAB). In addition, concentrations of monomethylmercury (CH(3)Hg(+)) were determined in diet fish and dolphins' tissue samples. The data were compared with the values found in wild populations to better understand how the dietary Hg and Se uptake rates affect the Hg and Se levels in dolphins. The diet fish total Hg concentrations ranged between 14 and 47 ng g(-1) and were markedly lower than for similar fish found in Florida, South Carolina, and other aquaria. CH(3)Hg(+) accounted for 85 to 91% of the total Hg found in diet fish. The diet fish Se concentrations ranged between 270 and 800 ng g(-1), indicating excess molar concentrations of Se over Hg. The Hg concentration range in the blood of NAB dolphins was 27-117 ng g(-1) and the concentrations were about one order of magnitude and several factors lower than the concentrations found in the blood of wild bottlenose dolphins in Florida and in South Carolina, respectively. The total Hg and CH(3)Hg(+) in tissue samples were also significantly lower than the reported values obtained from wild populations of bottlenose dolphins. The differences in the Hg concentrations in the dolphins' blood may be due to the different levels of Hg atmospheric deposition in the area where the dolphins' diet fish were found. The Se concentration range in the blood of NAB dolphins was 221-297 ng g(-1) which was two factors lower than the values found in wild populations. The lower Hg levels, as well as higher Se:Hg molar ratios in the blood of NAB dolphins, suggest that NAB dolphins may be less susceptible to the potential neurotoxicity from the CH(3)Hg(+) in their blood.

Aquatic and terrestrial stressors in amphibians: a test of the double jeopardy hypothesis based on maternally and trophically derived contaminants

Amphibians with biphasic life histories occupy aquatic and terrestrial habitats at different times in their lives, leading to a double jeopardy of contaminant risk in both habitats. The present study examines individual and interactive effects of mercury exposure to terrestrial adults and aquatic larvae on fitness-related traits of American toads, Bufo americanus. Eggs from reference mothers or contaminated mothers were allowed to hatch and larvae were fed diets of either no added Hg or 2.5 or 10 µg/g total Hg (dry wt). Both dietary and maternal Hg had adverse effects on developing larvae, but there was no interaction between these factors. Dietary Hg had a marginal effect of decreased survival with increasing Hg in the diet. Animals from Hg-exposed mothers weighed 14% less than those from reference mothers, and size at metamorphosis was directly correlated with hopping performance. Animals from Hg-exposed mothers also took longer to complete metamorphosis and had 2.5 times the prevalence of spinal malformations compared with those from reference mothers. Results of the present study demonstrate that amphibians do indeed face a double jeopardy of contaminant exposure stemming from terrestrial and aquatic environments, because both exposure pathways adversely affected developing offspring. The present study also demonstrates that all possible routes of exposure over an organism's life history must be examined to provide a comprehensive picture of the ecological consequences of habitat contamination.

Combination of diffusive gradient in a thin film probe and IC-ICP-MS for the simultaneous determination of CH3Hg+ and Hg2+ in oxic water

A diffusive gradient in thin film technique (DGT) was combined with ion chromatography and inductively coupled plasma mass spectrometry (IC-ICP-MS) for the in situ simultaneous quantification of CH(3)Hg(+) and Hg(2+) in aquatic environments. After diffusing through an agarose diffusive layer, the Hg species accumulated in a thiol-functionalized resin layer and were extracted using acidic thiourea solution to form stable thiourea-Hg complexes that were separated and detected via ion chromatography and ICP-MS, respectively. The effective diffusion coefficients of CH(3)Hg(+) and Hg(2+) complexes in the agarose diffusion layer with chloride were 5.26 (±0.27) × 10(-6) and 4.02 (±0.10) × 10(-6) cm(2) s(-1), respectively. The effective diffusion coefficients of CH(3)Hg(+) and Hg(2+) complexes in the agarose diffusion layer with dissolved organic matter was 3.57 (±0.29) × 10(-6) and 2.16 (±0.19) × 10(-6) cm(2) s(-1), respectively. The practical method detection limits are 0.1 and 0.7 ng L(-1) for CH(3)Hg(+) and Hg(2+) respectively for three weeks deployment. Lower detection limits would be possible by employing a thinner agarose diffusive layer and/or by deploying the probes longer. The method can measure time averaged CH(3)Hg(+) and Hg(2+) concentrations simultaneously in oxic water, making it useful as an in situ monitoring tool.

Automated speciation of mercury in the hair of breastfed infants exposed to ethylmercury from thimerosal-containing vaccines

A simplified thiourea-based chromatography method, originally developed for methyl and inorganic mercury, was adapted to separate methylmercury (MeHg), ethylmercury (EtHg), and inorganic mercury (Hg(II)) in infants' hair. Samples were weighed and leached with an acidic thiourea solution. Leachates were concentrated on a polymeric resin prior to analysis by Hg-thiourea liquid chromatography/cold vapor atomic fluorescence spectrometry. All but one sample showed small amounts of EtHg, and four of the six analyzed samples had proportionally higher Hg(II) as a percent of total Hg. Breastfed infants from riverine Amazonian communities are exposed to mercury in breast milk (from high levels of maternal sources that include both fish consumption and dental amalgam) and to EtHg in vaccines (from thimerosal). The method proved sensitive enough to detect and quantify acute EtHg exposure after shots of thimerosal-containing vaccines. Based on work with MeHg and Hg(II), estimated detection limits for this method are 0.050, 0.10, and 0.10 ng g⁻¹ for MeHg, Hg(II), and EtHg, respectively, for a 20-mg sample. Specific limits depend on the amount of sample extracted and the amount of extract injected.

Comparison of mercury concentrations in landlocked, resident, and sea-run fish (Salvelinus spp.) from Nunavut, Canada

Mercury concentrations ([Hg]) in Arctic food fish often exceed guidelines for human subsistence consumption. Previous research on two food fish species, Arctic char (Salvelinus alpinus) and lake trout (Salvelinus namaycush), indicates that anadromous fish have lower [Hg] than nonanadromous fish, but there have been no intraregional comparisons. Also, no comparisons of [Hg] among anadromous (sea-run), resident (marine access but do not migrate), and landlocked (no marine access) life history types of Arctic char and lake trout have been published. Using intraregional data from 10 lakes in the West Kitikmeot area of Nunavut, Canada, we found that [Hg] varied significantly among species and life history types. Differences among species-life history types were best explained by age-at-size and C:N ratios (indicator of lipid); [Hg] was significantly and negatively related to both. At a standardized fork length of 500 mm, lake trout had significantly higher [Hg] (mean 0.17 µg/g wet wt) than Arctic char (0.09 µg/g). Anadromous and resident Arctic char had significantly lower [Hg] (each 0.04 µg/g) than landlocked Arctic char (0.19 µg/g). Anadromous lake trout had significantly lower [Hg] (0.12 µg/g) than resident lake trout (0.18 µg/g), but no significant difference in [Hg] was seen between landlocked lake trout (0.21 µg/g) and other life history types. Our results are relevant to human health assessments and consumption guidance and will inform models of Hg accumulation in Arctic fish.

Mercury speciation and biomagnification in the food web of Caddo Lake, Texas and Louisiana, USA, a subtropical freshwater ecosystem

We studied the biomagnification of total mercury and methylmercury in a subtropical freshwater lake, Caddo Lake, Texas and Louisiana, USA. The present study is unique in that it not only included invertebrates (seven species) and fish (six species) but also an amphibian (one species), reptiles (three species), and mammals (three species). Nonfish vertebrates such as those included in the present study are often not included in assessments of trophic transfer of Hg. Mean trophic position (determined using stable isotopes of nitrogen) ranged from 2.0 (indicative of a primary consumer) to 3.8 (indicative of a tertiary consumer). Mean total Hg concentrations ranged from 36 to 3,292 ng/g dry weight in muscle and whole body and from 150 to 30,171 ng/g dry weight in liver. Most of the Hg in muscle and whole-body tissue was found as methylmercury, and at least 50% of the Hg found in liver was in the inorganic form (with the exception of largemouth bass, Micropterus salmoides). Mercury concentrations were positively correlated with trophic position, indicating that biomagnification occurs in the food web of Caddo Lake. The food web magnification factors (FWMFs; slope of the relationship between mean Hg concentration and trophic position) for both total Hg and methylmercury were similar to those observed in other studies. Because most of the total Hg in consumers was methylmercury, the FWMF for methylmercury was not significantly different from the FWMF for total Hg. Some vertebrates examined in the present study had low Hg concentrations in their tissues similar to those observed in invertebrates, whereas others had concentrations of Hg in their tissues that in previous studies have been associated with negative health consequences in fish.

Mercury concentrations in Arctic food fishes reflect the presence of anadromous Arctic charr (Salvelinus alpinus), species, and life history

Single-spawning (semelparous) anadromous fishes are known to transport contaminants from marine to freshwater habitats, but little research has been conducted on contaminant biotransport by multiple-spawning (iteroparous) anadromous fishes. We examined the effect of iteroparous, anadromous Arctic charr (Salvelinus alpinus) on mercury concentrations ([Hg]) in freshwater biota and compared [Hg] between species and life history types of Arctic charr and lake trout (Salvelinus namaycush). Data from six lakes and one coastal marine area in the Arctic territory of Nunavut, Canada, indicated that 1) lake trout had significantly lower [Hg] in lakes where anadromous Arctic charr were present; 2) [Hg] was significantly lower in recently discovered anadromous lake trout than in resident lake trout; and 3) regardless of life history, Arctic charr had significantly lower [Hg] than lake trout. These differences were explained by fish condition, age-at-size, and C:N. Biomagnification of Hg, measured as log(10)[Hg]-delta(15)N slopes, did not differ between lakes with and without anadromous Arctic charr but was significantly higher in freshwater food webs ( approximately 0.2) than in the marine food web (0.08). Some biomagnification estimates were affected by correction for fish age and size. In contrast to semelparous anadromous species, biotransport of Hg by anadromous Arctic charr appears to be offset by increased growth of freshwater fishes.

Bioaccessibility of mercury from traditional northern country foods measured using an in vitro gastrointestinal model is independent of mercury concentration

Human health risk assessment of dietary mercury (Hg) exposure in Canada assumes that all Hg from fish consumption is in the form of methylmercury (MeHg), the more bioavailable and hazardous form of Hg. In contrast, the risk assessment of dietary Hg to Inuit in northern Canada assumes that no more than two-thirds of dietary Hg is MeHg since mammal organs consumed by Inuit contain substantial concentrations of inorganic Hg. In vitro gastrointestinal models (e.g., the Simulator of the Human Intestinal Microbial Ecosystem) are often used for the evaluation of soil contaminant bioaccessibility, i.e., the fraction solubilized into gastrointestinal fluids, for use in site-specific human health risk assessment. In this research, we digested northern country foods using the SHIME for the measurement of Hg bioaccessibility, a novel approach for the assessment of dietary Hg bioavailability. We demonstrated that small intestinal Hg bioaccessibility from 16 fish, wild game, and marine mammal samples consumed by Inuit in northern Canada ranged between 1 and 93% and was independent of food HgT (MeHg+Hg(II)) concentration. Additionally, we demonstrated that gastrointestinal microbes may affect Hg bioaccessibility of the 16 country foods, either increasing or decreasing bioaccessibility depending upon the type of food. These results indicate that gastrointestinal absorption of Hg is not likely limited by the concentration of Hg in the food, which is in agreement with in vivo Hg bioavailability studies. Furthermore, these in vitro results support the hypothesis that the gastrointestinal absorption of Hg from Inuit country foods is dependent upon food type.