Hg Bioaccumulation Research Articles

Bioaccumulation of Hg, Cr, Zn, As, Cd, Pb, Cu in the “soil-plant” system in the area of influence of enterprises for the production and processing of batteries

Bioaccumulation of Hg, Cr, Zn, As, Cd, Pb, Cu in the “soil-plant” system in the area of influence of enterprises for the production and processing of batteries

Mercury Concentration in Liver Tissues of South American Fur Seals (Arctocephalus australis) from Southwestern Atlantic Ocean

Mercury (Hg) contamination of oceans is rapidly increasing, however Hg bioaccumulation in pinnipeds has been understudied. Here, we report for the first time Hg concentration in liver tissues of South American fur seals (Arctocephalus australis) in South and Southeast Brazil. Hg concentration was determined in twenty-five fur seals’ specimens found stranded along the coast of the Southwestern Atlantic Ocean. Samples were digested using the microwave technique and quantified by cold vapor generation atomic fluorescence spectrometry technique. The average Hg concentration was 6.37 mg kg-1 (wet weight), with a minimum concentration of 0.09 mg kg-1 and the highest concentration of 15.58 mg kg-1. No correlation between biological variables (sex, total length and weight) and Hg concentration in A. australis liver were found. The results presented here are of great importance to establish baselines for future evaluations of Hg contamination in marine mammals and the effects of this environmental problem in animal health.

Alteration of acute toxicity of inorganic and methyl mercury to Daphnia magna by dietary addition

Acute toxicity of inorganic mercury [Hg(II)] and methylmercury (MeHg) to Daphnia magna was characterized using a 48-h static, non-renewal acute toxicity test, in which we compared the toxicity of Hg(II) and MeHg in the absence (water-only) and presence of diet [green alga (Raphidocelis subcapitata), yeast, Cerophyll, and trout chow (YCT), or both]. Overall, Hg(II) is more toxic to D. magna than MeHg, with 48-h median lethal concentrations (LC50s) being 4.3 µg/L (95% confidence interval: 4.1–4.5 µg/L) for Hg(II) and 14.3 µg/L (13.2–15.3 µg/L) for MeHg. For Hg(II), the addition of any diet would significantly increase its 48-h LC50, but the 48-h LC50 for MeHg decreased significantly to 7.1 µg/L (6.4–7.8 µg/L) with the algal addition. We also show that the addition of diets significantly influenced the levels and speciation (dissolved vs. particulate) of both Hg forms in the test solution. The bioaccumulation of Hg(II) and MeHg was impacted by the dietary addition, and it appears that the body residue level triggering mortality varied widely among treatments. The results suggest that standard short-term toxicity tests (water-only) should be supplemented with extra tests with dietary addition to provide a more environmentally relevant estimation of short-term toxicity of chemical compounds.

Reduction in mercury bioavailability to Asian clams (Corbicula fluminea) and changes in bacterial communities in sediments with activated carbon amendment

Activated carbon (AC) amendment is considered as one of the alternatives for managing and remediating mercury (Hg) contaminated sediments because of its high sorptive capacity and potential to immobilize the contaminant. For this study, the underlying mechanisms that control the reduction of Hg bioavailability in AC-amended estuarine sediments were investigated in box microcosm set-ups with 28-day Asian clam bioassay experiments. The application of diffusive gradients in thin film technique (DGT) revealed that the total mercury and methylmercury levels in sediment pore water decreased by 60%–75% in 1%–3% AC-amended sediments. This decrease subsequently led to a linear reduction in the Hg body burden in Asian clams, even at 1% sorbent mixing. These observations implied that AC amendment reduced the net flux of Hg into the pore water and overlying water, resulting in reduced Hg bioaccumulation in benthic organisms. The addition of AC to sediment also led to reduced dissolved organic carbon and several biogeochemical indicators (HS−, Mn, and Fe) in the pore water. Furthermore, the 16 S rRNA gene amplicon sequencing analysis revealed noticeable alterations in the microbial communities after AC amendment. The predominant phylum was Firmicutes in control sediment, Bacteroidetes in 1% AC-amended sediment, and Proteobacteria in both 2% and 3% AC-amended sediment samples. The genera-level analysis showed that the relative abundance of the Hg-methylators decreased as the level of AC amendment increased. These observations suggested that AC amendment decreased Hg bioavailability not only by physicochemical sorption but also by changing geochemical species and shifting the microbial community composition.

Mapping the distribution of mercury (II) chloride in zebrafish organs by benchtop micro-energy dispersive X-ray fluorescence: A proof of concept

BackgroundMercury (Hg) is a globally ubiquitous pollutant and one of the most dangerous metal contaminants, which presents a high risk of bioaccumulation in living organisms. In this study, we mapped the distribution of Hg and other trace elements in zebrafish (Danio rerio), which were exposed to mercury (II) chloride in order to assess its toxicity, bioaccumulation and distribution in fish organs. MethodsAdult zebrafish were exposed for 7 days to different concentrations of mercury (II) chloride and the elemental distribution was obtained through the micro-energy dispersive X-ray fluorescence technique (μ-EDXRF). ResultsThe results showed that Hg levels, measured in fish tissues, were indicative of bioaccumulation within some of its organs (e.g. visceral mass, gills), and that the physiological processes of accumulation were highly dose-dependent. In addition, the results showed higher concentrations of Hg in the gills. Moreover, other trace elements (e.g. Fe, Cu and Zn) levels were not altered after fish exposure to mercury(II) chloride. ConclusionThe μ-EDXRF results were assessed along with the determination of some oxidative stress biomarkers (e.g. antioxidant enzymes) to understand the effects behind the Hg bioaccumulation and toxicity. These results suggest that the metabolic changes in zebrafish due to the exposure to Hg are consistent with oxidative stress.

Bluefin tuna reveal global patterns of mercury pollution and bioavailability in the world's oceans

Bluefin tuna (BFT), highly prized among consumers, accumulate high levels of mercury (Hg) as neurotoxic methylmercury (MeHg). However, how Hg bioaccumulation varies among globally distributed BFT populations is not understood. Here, we show mercury accumulation rates (MARs) in BFT are highest in the Mediterranean Sea and decrease as North Pacific Ocean > Indian Ocean > North Atlantic Ocean. Moreover, MARs increase in proportion to the concentrations of MeHg in regional seawater and zooplankton, linking MeHg accumulation in BFT to MeHg bioavailability at the base of each subbasin's food web. Observed global patterns correspond to levels of Hg in each ocean subbasin; the Mediterranean, North Pacific, and Indian Oceans are subject to geogenic enrichment and anthropogenic contamination, while the North Atlantic Ocean is less so. MAR in BFT as a global pollution index reflects natural and human sources and global thermohaline circulation.

The alteration of gut microbiome community play an important role in mercury biotransformation in largemouth bass

Mercury (Hg) biotransformation is an important process that can affect the speciation and bioaccumulation of Hg in fish. The intestinal microbiota has been suggested to take part in this process. However, Hg biotransformation in fish is still unclear and the responses of gut microbiota to different Hg exposure scenarios have not been well addressed. The present study investigated the bioaccumulation and biotransformation of Hg in a freshwater fish (Micropterus salmoides) and characterized the gut microbiome community under dietary inorganic Hg (IHg) or methylmercury (MeHg) exposure, aiming to evaluate the effects of gut microbiome's activities on the internal-handling and fate of Hg in fish. Significant Hg methylation was observed in fish under IHg exposure, whereas there was no demethylation occurred in MeHg-treated fish. Both IHg and MeHg could significantly alter the community composition of gut microbiome. The administrated IHg in the food could enhance the growth of methylators, resulting in additional MeHg production in fish gut. However, abundance of demethylators was greatly decreased under either IHg or MeHg exposure, leading the demethylation process to be negligible. The results strongly suggested that the behaviors of gut bacterial community played an important role in the presence or absence of biotransformation processes. This study elucidated the importance of gut microbiome in Hg biotransformation process, and helped to develop a novel perspective to understand the Hg bioaccumulation of fish in realistic environment.

Mercury bioaccumulation by higher plants and mushrooms around chlor-alkali and metallurgical industries in the Baikal region, Southern Siberia, Russia

ABSTRACT This investigation identified specific features of mercury bioaccumulation by higher plants and mushrooms growing around chlor-alkali and metallurgical plants. All samples analysed by the atomic absorption method. Various plant organs differently accumulate mercury that is regulated by their biochemical and physiological functions. Examination of different plant parts points out that the leaves and bark of trees and the leaves of herbs are the main Hg accumulators, which is explained both by the absorption of soil mercury and Hg input from the atmospheric air. The plants from the АМР surroundings show lower Hg concentrations (average 0.008 mg kg−1) when compared with those from the САР surroundings (average 0.040 mg kg−1). Mushrooms exhibit the highest bioaccumulation of Hg amount in the studied samples. The average Hg concentrations in mushrooms in CAP and AMP amount to 0.78 and 0.19 mg kg−1, accordingly. These concentrations are higher than Hg concentrations in soils, in which these mushrooms were growing. The ability of plants and mushrooms to take up mercury is directly related to its bioavailable forms in soils. The Hg–organic complexes play a crucial role the Hg bioaccumulation that is evidenced by a significant positive correlation in the ‘organic Hg fraction–plants’ system.

Mercury resistance and plant growth promoting traits of endophytic bacteria isolated from mercury-contaminated soil

Mercury (Hg) is a toxic trace element that can cause serious environmental problems. The main source of Hg contamination to soil across Indonesia is artisanal and small-scale gold mining (ASGM) and strategies to manage or remove Hg from soil are needed. This study isolated Hg-resistant endophytic bacteria from indigenous local grasses (Cynodon dactylon and Eleusine indica) growing in Hg-contaminated soils to identify potential inoculants that could increase plant growth and mercury uptake for phytoremediation. Grass samples were collected from an ASGM location on Lombok Island. The grass samples (both, root and shoot) were surface sterilized, aseptically mashed, and serially diluted with 0.9% sodium chloride (v/v) and an aliquot of the extracted bacteria was cultured on Nutrient Agar across a range of HgCl2 concentration from 0 to 1000 mg/L. Thirteen bacterial isolates were tested for their ability to detoxify Hg, Hg bioaccumulation, indole acetic acid (IAA) production, ammonium production, and siderophore production. Five of thirteen isolates were Hg-resistant and survived on a medium containing 250 mg/L HgCl2. One isolate from each of E. indica and C. dactylon showed complete Hg detoxification. The greatest Hg bioaccumulation was 85.04%. The highest expressed IAA and ammonium concentration was 13.17 mg/L and 2.58 mg/L respectively. Based on 16S rDNA sequence similarity, the two isolates with the greatest potential as inoculants (CD6 and EI6) were identified as Jeotgalicoccus huakuii (isolated from C. dactylon) and Bacillus amyloliquefaciens (isolated from E. indica) and could be used as inoculum for phytoremediation of Hg-contaminated soil in future studies.

Mercury contamination in terrestrial predatory birds from Northeast China: Implications for species and feather type selection for biomonitoring

Mercury (Hg), a persistent potent neurotoxin, poses a serious hazard to human and wildlife health. Although highly elevated concentrations were documented in the environmental compartments of China, very few investigations were conducted regarding Hg bioaccumulation in terrestrial vertebrates, particularly avian species at the top trophic position. To assess to what degree the predatory raptors are subject to Hg contamination, we measured feather Hg concentrations from two diurnal raptors, two nocturnal owls, and one predatory passerine, collected from Northeast China. Results showed that the feather Hg concentrations were not greater than 3.67 mg/kg. Notably, there is a significant difference in feather Hg among species: Brown Shrike > Amur Falcon = Common Kestrel > Long-eared Owl > Little Owl. Brown Shrike had the highest feather Hg (1.27 ± 0.91 mg/kg), approximately three times higher compared to the diurnal predators (0.41 ± 0.33 mg/kg), and about seven-folds higher than the owls (0.18 ± 0.19 mg/kg). There were no differences in Hg concentrations between the tips of primary and tail feathers, but their correlations were significantly positive (between 0.45 and 0.96). Overall, the primary Hg = 0.15 + 0.74 × tail Hg (R2 = 0.61). Specifically, a great correlation between the primaries and tails in owls, while a weaker but significant correlation found in falcons/shrikes, provides insight into Hg content in feather tracts for biomonitoring. Our research is among the few studies regarding Hg contamination in the terrestrial predatory avian population in China. We discussed the influencing factors, the ecotoxicological risks to the terrestrial/marine avian population, and the limitations of this research.

Mercury accumulation in reef fishes: a comparison among red grouper, scamp, and gag of the Atlantic southeastern US and evaluation of "grouper" consumption guidelines.

In fish consumption advisories pertaining to Hg, grouper species in the family Serranidae are often lumped together and labeled generically as Grouper. However, grouper species vary considerably in growth rate, maximum age, and maximum size. This study examined the variability of Hg concentrations and bioaccumulation rates (increase of Hg concentrations in relation to age) for populations of three long-lived, slow-growing, protogynous hermaphrodite grouper species, gag Mycteroperca microlepis, scamp M. phenax, and red grouper Epinephelus morio, which are commercially and recreationally important in the offshore waters of the US southeastern region. A total of 268 samples from the three grouper species were processed for Hg analysis from 2013-2015. Concentrations of Hg ranged from 0.03 to 0.87ppm wet weight, with a mean of 0.30ppm. Gag accumulated Hg at a faster rate (as measured by the increase of Hg with fish age) than the other two species. Size, age, and δ15N were significant predictors for Hg in the two Mycteroperca species, while size and age were significant predictors for Hg in red grouper. Two of the three species had mean Hg concentrations within the one meal per week "Good Choices" consumption category (red grouper and scamp), and one species (gag) had a mean Hg level within the two meals per week "Good Choices" consumption category as advised by the US EPA and US FDA. These results support the separation of grouper species in advisories.

Rapid temporal decline of mercury in Greenland halibut (Reinhardtius hippoglossoides)

Mercury (Hg) pollution in the ocean is an issue of global concern, however bioaccumulation regimes of this ubiquitous pollutant in marine apex predators have important knowledge gaps. Our fish length and stable isotope (δ15N and δ13C) normalized data of Greenland halibut (GH) (Reinhardtius hippoglossoides) showed that Hg bioaccumulation in fillet tissue decreased by ~35–50 %, over a ten-year period from 2006 to 2015 (n = 7 individual sampling years). Hg was predominantly in the methylmercury form (>77 %). Results from a Bayesian information theoretic model showed that GH Hg concentrations decreased with time and its associated declines in Hg air emissions, estimated trophic position, and a potentially lower degree of demersal prey use as indicated by temporal trend shifts in nitrogen (δ15N) and carbon (δ13C) stable isotope values. GH trophic shifts accounted for about one third of the observed temporal reduction in Hg. Our study demonstrates the importance of simultaneously considering Hg emissions, food web dynamics and trophic shifts as important drivers of Hg bioaccumulation in a marine, deep water fish species and highlights the effectiveness of Hg regulations on ocean apex predator Hg concentrations and overall seafood safety.

Assessment of Hg accumulation in fish and scalp hair in fishing communities along river Swat, Pakistan.

Mercury (Hg) bioaccumulation in fish poses severe threats to the food safety and human health. This study was conducted to assess Hg bioaccumulation in fish (n = 24) and scalp hair (n = 77) of the fishing communities at up- and downstream of the river Swat, Pakistan. The mean Hg concentration in upstream fish Salmo trutta fario (Brown trout) and Schizothorax plagiostomus (Swati fish) species was 34.7±18 μg kg-1 and 29.4±15 μg kg-1, respectively. The mean Hg concentration in downstream Swati fish, Crossocheilus diplochilus (Spena deqa), and Garra gotyla (Tora deqa) was 65±21 μg kg-1, 123±33 μg kg-1, and 326±53 μg Kg-1, respectively. The mean Hg concentration in scalp hair of the up- and downstream fishing communities was 658±125 μg kg-1 and 3969±791 μg kg-1, respectively. Independent T-test showed significant difference (p < 0.001) in the mean Hg concentration in scalp hair of the up- and downstream communities. The most prevalent health problems found in the fishing community were muscle pain, headache, visual impairment, arterial blood pressure, anemia, and kidney dysfunction. Multiple linear regression indicated that daily and weekly consumption of the fish significantly increase Hg accumulation in human scalp hair. Regular consumption of fruits and cruciferous and leafy vegetables were found to reduce Hg toxicity in the population. Further studies are recommended to identify the sources of Hg and welfare impact of fish contamination on the fishing community of river Swat.

Species-specific isotope tracking of mercury uptake and transformations by pico-nanoplankton in an eutrophic lake

The present study aims to explore the bioaccumulation and biotic transformations of inorganic (iHg) and monomethyl mercury (MMHg) by natural pico-nanoplankton community from eutrophic lake Soppen, Switzerland. Pico-nanoplankton encompass mainly bacterioplankton, mycoplankton and phytoplankton groups with size between 0.2 and 20 μm. Species-specific enriched isotope mixture of 199iHg and 201MMHg was used to explore the accumulation, the subcellular distribution and transformations occurring in natural pico-nanoplankton sampled at 2 different depths (6.6 m and 8.3 m). Cyanobacteria, diatoms, cryptophyta, green algae and heterotrophic microorganisms were identified as the major groups of pico-nanoplankton with diatoms prevailing at deeper samples. Results showed that pico-nanoplankton accumulated both iHg and MMHg preferentially in the cell membrane/organelles, despite observed losses. The ratios between the iHg and MMHg concentrations measured in the membrane/organelles and cytosol were comparable for iHg and MMHg. Pico-nanoplankton demethylate added 201MMHg (~4 and 12% per day depending on cellular compartment), although the involved pathways are to further explore. Comparison of the concentrations of 201iHg formed from 201MMHg demethylation in whole system, medium and whole cells showed that 82% of the demethylation was biologically mediated by pico-nanoplankton. No significant methylation of iHg by pico-nanoplankton was observed. The accumulation of iHg and MMHg and the percentage of demethylated MMHg correlated positively with the relative abundance of diatoms and heterotrophic microorganisms in the pico-nanoplankton, the concentrations of TN, Mg2+, NO3−, NO2−, NH4+ and negatively with the concentrations of DOC, K+, Na+, Ca2+, SO42−. Taken together the results of the present field study confirm the role of pico-nanoplankton in Hg bioaccumulation and demethylation, however further research is needed to better understand the underlying mechanisms and interconnection between heterotrophic and autotrophic microorganisms.

Bioaccumulation of lead (Pb) and mercury (Hg) in green mussel Perna viridis (Linnaeus, 1758) in Cengkok Coastal Waters, Banten Bay, Indonesia

Banten Bay potentially receives pollutants such as heavy metals from various anthropogenic activities operating around the bay. Cengkok Coastal Waters, as part of Banten Bay, has a variety of fishery commodities, including green mussels (Perna viridis). This paper identifies the risks of heavy metal contamination by quantifying the bioaccumulation of Pb and Hg in the green mussel tissue. The study was conducted from March to August 2019. Analytical results indicate concentrations of Pb and Hg in the range of 0.005-0.044 mg/kg and 0.012-0.036 mg/kg, respectively. These results were still below the established national standards by SNI (2009) for fresh food and BPOM (2018) for processed food. These concentrations suggest that green mussel found in Cengkok Coastal Waters and surrounding areas are still suitable for consumption by the local community as long as they do not exceed the permissible limits, namely, 0.7 kg meat/week (for children) and 2.4 kg meat/week (for adults).

Distributions of Total Mercury and Methylmercury in Dragonflies from a Large, Abandoned Mercury Mining Region in China.

Dragonflies (Order Odonata) often are considered to be biosentinels of environmental contamination, e.g., heavy metals and/or persistent organic pollutants (POPs). Dragonflies (n = 439) belonging to 15 species of 8 genera were collected from an abandoned mercury (Hg) mining region in China to investigate the bioaccumulation of total Hg (THg) and methylmercury (MeHg). THg and MeHg concentrations in dragonflies varied widely within ranges of 0.06-19mg/kg (average: 1.5 ± 2.2mg/kg) and 0.02-5.7mg/kg (average: 0.75 ± 0.65mg/kg), respectively. THg and MeHg were positively correlated with bodyweight (THg: r2 = 0.10, P = 0.000; MeHg: r2 = 0.09, P = 0.000). Significant variations were observed among species, with the highest MeHg value (in Orthetrum triangulare) was fivefold higher than the lowest (in Pantala flavescens). These variations were consistent with those of nitrogen isotope (δ15N) values, indicating that increased δ15N, i.e., trophic levels, may reflect increased exposure and uptake of biomagnifying MeHg in dragonflies. A toxicologicalrisk assessment found hazard quotients for specialist dragonfly-consuming birds of up to 7.2, which is 2.4 times greater than the permissible limit of 3, suggesting a potential toxicological risk of exposure.

Effects of Mercury Contamination on The Physiology of Purple Martins ( Progne subis )

Purple Martins (Progne subis) are insectivorous birds that spend their breeding season in North America before migrating to South America, where they molt. Many individuals migrate to the Amazon basin, a region of high mercury (Hg) contamination, which raises the possibility that observed declines in Purple Martins could be linked to mercury exposure. Hg is a toxic heavy metal; exposure to and bioaccumulation of Hg can result in numerous and systemic negative health outcomes, including disruption of hormones like Corticosterone (B) and triiodothyronine (T3). Both play important roles in metabolic regulation in migratory birds. Feathers, tissues that accumulate Hg and hormones during growth and can thus be used as a proxy to assess a bird's Hg load and endocrine profile. The objective of this study is to assess interrelationships among total Hg (THg), B and T3 concentrations in feathers grown in the Amazon and reproductive (productivity) and body condition (mass, fat score) endpoints. We assayed tail feathers from 80 Purple Martins from their breeding grounds in Florida, Virginia, and Wisconsin. The concentration of THg in Purple Martins’ feathers ranged from 1.103 ug/g dw to 8.740 ug/g dw, which is above the level at which physiological impacts have been observed in studies of other avian species. Hg concentration did not significantly differ by sampling locations or correlate with either B, T3 or nest productivity. However, THg concentration negatively correlated with both mass and fat score. Both B and T3 concentrations were significantly higher in Florida than in the other two states, but neither showed correlations with biometric data or nest productivity. Furthermore, B concentrations in three birds from Florida were much higher than the basal range and may indicate a high stress condition during feather-growth in South America. Taken together, our findings suggest that concentrations of THg in Purple Martins’ feathers are high enough to be a cause of concern. The results show that THg concentration negatively impacts the ability of Purple Martins to accumulate fat, which can present a deleterious effect for a migratory bird. This result also indicates carryover effects of Hg contamination at the wintering grounds to the summer breeding grounds, where fat score was measured. The impact on fat accumulation, however, did not appear to be caused by Hg disruption of T3 or B at the time of feather-growth. Nevertheless, endocrine disruption by Hg could still have happened at a later moment. These physiological impacts suggest a possible mechanism by which high THg exposure in the nonbreeding grounds could negatively impact purple martins and have contributed to observed population declines over the last several decade.

Characterization of River Sediments in Loja-Ecuador

This research's main objective is to delineate areas with a high concentration of "pollutant" elements that imply a risk for the ecosystem and inhabitants' health in the Cordillera Real, south of Ecuador. To this end, a survey was carried out applying statistical analysis of the data. Specifically, the method of ordinary Kriging and Lepeltier is used to sort the data in populations according to their concentration. Previously, the information was compared with national (TULAS) and international regulations (Environmental Canada). These metals' spatial distribution is shown in concentration maps for each element (Hg, Pb, Zn, As, and Cu), where the potential villages exposed to these anomalies are displayed. In this sense, the samples' chemical digestion was conducted to quantify the atomic emission technique's before-mentioned pollutants' concentration. It was also correlated with geology, mineral occurrences, and metallogeny evidence to conclude that Pb and Zn anomalies are related to San Lucas granodiorite's intrusion, whereas Cu and Hg with local mineralization of sulfides, and as may be with domestic and industrial discharges. Finally, even though the anomalous concentrations of metallic elements were found to be characteristic of the lithology, cautions should be taken to safeguard the health of people and agriculture because there is evidence of elements such as As and Hg bioaccumulation in species that are part of the food chain.

Regional variation in mercury bioaccumulation among NW Atlantic Golden (Lopholatilus chamaeleonticeps) and Blueline (Caulolatilus microps) Tilefish

Mercury (Hg) concentrations in fishes from the NW Atlantic Ocean pose concern due to the importance of this region to U.S. fisheries harvest. In this study, total Hg (THg) concentrations and nitrogen stable isotope (δ15N) values were quantified in muscle tissues sampled from Golden (Lopholatilus chamaeleonticeps) and Blueline (Caulolatilus microps) Tilefish collected during a fishery-independent survey conducted in the NW Atlantic to compare bioaccumulation patterns between these species. Total Hg concentrations averaged (±SD) 0.4 ± 0.4 μg/g dry weight (d.w.) for L. chamaeleonticeps and 1.1 ± 0.7 μg/g d.w. for C. microps with <2% of all sampled fish, those >70 cm fork length, exceeding the most restrictive USEPA regulatory guidelines for human consumption (THg > 0.46 μg/g w.w.), when converted to wet weight concentrations. The THg concentrations reported here for individuals from the NW Atlantic stock are comparable to those reported for similarly sized individuals collected from the SW Atlantic stock but notably lower than those reported for Gulf of Mexico L. chamaeleonticeps, indicating different Hg exposure and assimilation kinetics for fish from the NW Atlantic, and highlights the broad geographic variability of Hg bioaccumulation among Tilefish stocks. Caulolatilus microps had higher δ15N values relative to L. chamaeleonticeps and a pattern of decreasing THg concentrations was also present from south to north across the study range. It is concluded that this trophic difference and spatial pattern in Tilefish THg concentrations emphasizes the habitat and resource partitioning mechanisms described for these sympatric species that permits their coexistence in the continental shelf environment. Importantly, regional variability in THg concentrations accentuate the possible roles of fine-scale biotic and abiotic processes that can act to regulate Hg bioaccumulation among individuals and species.

Bioaccumulation of mercury and transcriptional responses in tusk (Brosme brosme), a deep-water fish from a Norwegian fjord

High concentrations of mercury (Hg) have been documented in deep-water fish species from some Norwegian fjords. In this study, tusk (Brosme brosme) was sampled from four locations in the innermost parts of Sognefjorden in Western Norway. Total Hg and methylmercury (MeHg) levels were measured in liver tissue. To search for potential sublethal effects of Hg, we characterized the hepatic transcriptome in tusk with high and low levels of Hg bioaccumulation using global transcriptomics analysis (RNA-seq). The results showed that there was a significant correlation between fish weight and accumulated concentrations of MeHg but not total Hg. MeHg accounted for 30–40% of total Hg in liver of most of the fish, although at concentrations above 2–3 mg Hg/kg wet weight the percentage of MeHg dropped considerably. Transcriptome analysis resulted in hundreds of differentially expressed genes in the liver of tusk with high Hg levels. Functional enrichment analysis suggested that the top affected pathways are associated with protein folding, adipogenesis, notch signaling, and lipid metabolism (beta-oxidation and phospholipids). Based on transcriptional responses pointing to well-known effects of Hg compounds in fish, the study suggests that tusk in Sognefjorden could be negatively impacted by Hg bioaccumulation.