Total Mercury Research Articles

Effect of environmental variables on mercury accumulation in sediments of an anthropogenically impacted tropical estuary (Buenaventura Bay, Colombian Pacific)

Estuaries are the main entry areas of mercury to the marine environment and are important to understand the effect of this contaminant on marine organisms, since it accumulates in the sediments becoming available to enter the food trophic chain. This study aims to determine the environmental variables that mainly influence the spatiotemporal dynamics of total mercury accumulation in sediments of tropical estuaries. Sediment samples were collected from interior and exterior areas of the estuary during the dry and rainy seasons, representing the spatiotemporal gradients of the estuary. The grain size, organic matter content (OM), and total mercury concentration (THg) of the sediment samples were determined. In addition, salinity, temperature, dissolved oxygen, and pH of the water column associated with each sediment sample were assessed. The variations in environmental conditions, OM and THg in sediment were in accordance with a gradient which goes from conditions influenced by fresh water in the inner estuary to conditions influenced by sea water in the outer part of the estuary. The OM and THg in sediments presented similar variation patterns; they were higher in the rainy season than in the dry season and in the interior area of the estuary than in the exterior area. Despite the complex dynamic observed in the distribution and accumulation processes of mercury in sediments, these processes could be modeled from OM and salinity parameters. Due to the correlations found, in the process of accumulation of mercury in sediments the OM could represents the pathway of transport and accumulation of THg, and salinity could represent the influence of the hydroclimatic variations and environmental gradients of the estuary.

Glacial Erosion Drives High Summer Mercury Exports from the Yukon River, Canada.

Mercury concentrations and yields in the Yukon River are the highest of the world's six largest panarctic drainages. Permafrost thaw has been implicated as the main driver of these high values. Alternative sources include mercury released from glacial melt and erosion, atmospheric mercury pollution, or surface mining. To determine the summer source and speciation of mercury across the Yukon River basin within Canada, we sampled water from 12 tributaries and the mainstem during July 2021. The total (unfiltered) mercury concentration in the glacier-fed White River was 57 ng/L, >10 times higher than all other sampled tributaries. The White River's high total mercury concentrations were driven by suspended sediment and persisted ∼300 km downstream of glacierized headwaters. Total mercury concentrations were lowest (typically <2 ng/L) in tributaries downstream of still-water landscape features (e.g., lakes and settling ponds), suggesting these features are effective sinks for sediment-bound mercury. Low total mercury concentrations (∼2 ng/L) were also observed in five tributaries across diverse thawing permafrost landscapes. These results suggest that glacial erosion and meltwater transport, not permafrost, drive enhanced exports of mercury with suspended sediment. Mercury exports may decline as glacial watersheds pass peak water. Other factors, including mercury released from permafrost thaw, are minor components at present.

Climate change dynamics and mercury temporal trends in Northeast Arctic cod (Gadus morhua) from the Barents Sea ecosystem

The Northeast Arctic cod (Gadus morhua) is the world's northernmost stock of Atlantic cod and is of considerable ecological and economic importance. Northeast Arctic cod are widely distributed in the Barents Sea, an environment that supports a high degree of ecosystem resiliency and food web complexity. Here using 121 years of ocean temperature data (1900–2020), 41 years of sea ice extent information (1979–2020) and 27 years of total mercury (Hg) fillet concentration data (1994–2021, n = 1999, ≥71% Methyl Hg, n = 20) from the Barents Sea ecosystem, we evaluate the effects of climate change dynamics on Hg temporal trends in Northeast Arctic cod. We observed low and consistently stable, Hg concentrations (yearly, least-square means range = 0.022–0.037 mg/kg wet wt.) in length-normalized fish, with a slight decline in the most recent sampling periods despite a significant increase in Barents Sea temperature, and a sharp decline in regional sea ice extent. Overall, our data suggest that recent Arctic amplification of ocean temperature, “Atlantification,” and other perturbations of the Barents Sea ecosystem, along with rapidly declining sea ice extent over the last ∼30 years did not translate into major increases or decreases in Hg bioaccumulation in Northeast Arctic cod. Our findings are consistent with similar long-term, temporal assessments of Atlantic cod inhabiting Oslofjord, Norway, and with recent investigations and empirical data for other marine apex predators. This demonstrates that Hg bioaccumulation is highly context specific, and some species may not be as sensitive to current climate change-contaminant interactions as currently thought. Fish Hg bioaccumulation-climate change relationships are highly complex and not uniform, and our data suggest that Hg temporal trends in marine apex predators can vary considerably within and among species, and geographically. Hg bioaccumulation regimes in biota are highly nuanced and likely driven by a suite of other factors such as local diets, sources of Hg, bioenergetics, toxicokinetic processing, and growth and metabolic rates of individuals and taxa, and inputs from anthropogenic activities at varying spatiotemporal scales. Collectively, these findings have important policy implications for global food security, the Minamata Convention on Mercury, and several relevant UN Sustainable Development Goals.

Ecological risk of mercury in bottom sediments and spatial correlation with land use in Neotropical savanna floodplain lakes, Araguaia River, Central Brazil

The Araguaia River floodplain is an important biogeographic boundary between the two largest South American biomes: the Cerrado (Brazilian Savanna) and the Amazon rainforest. The large-scale degradation due to land use conversion experienced in the Araguaia River watershed represents a potential source of mercury (Hg) transport to aquatic ecosystems. However, more information is needed about the dynamics of Hg distribution in savanna floodplains, including the Araguaia River floodplain. We analyzed total mercury (THg) concentrations in the bottom sediments of 30 lakes connected to the Araguaia River and four tributaries, aiming to evaluate the environment's integrity based on the geoaccumulation index (Igeo) and the ecological risk index (ERI). The principal component analysis was applied to examine associations between Hg concentrations, environmental conditions, and land use intensity among lakes associated with different river systems. We used indicator cokriging to identify areas with a greater probability of Hg pollution and ecological risk associated with land use intensity. The land use data showed the predominance of areas used for pasture in the Araguaia River basin. THg concentrations in the sediments varied between 22.6 and 81.9 ng g−1 (mean: 46.5 ± 17.7 ng g−1). Sediments showed no significant pollution (Igeo: 1.35 - 0.50; Classes 1 and 2) and low to considerable ecological risks (ERI: 23.5–85.1; Classes 1 to 3). THg in bottom sediments was associated with land use, water turbidity and electrical conductivity, and sediment organic matter. The indicator cokriging indicates a moderate to strong spatial dependence between land use intensity and Hg, confirming the contribution of anthropic sources to the increment of ecological risk but also the influence of extrinsic factors (such as environmental conditions, geology, and hydrology). Integrating sediment assessment and land use indices with geostatistical methods proved a valuable tool for identifying priority areas for Hg accumulation at a regional scale.

Mercury concentration in the snow cover of the city of Khabarovsk

The research reveals results of studies of the total mercury content in the snow cover of Khabarovsk in winter period 2021-2022. Researchers highlight a connection between mercury and non-soluble residue, with minor transition into soluble phase. The total mercury content in the non-soluble residue ranged from 0.3 to 1.4 mg/kg. On the northern border of the Bolshekhekhtsirsky Reserve, area with high content of quicksilver (3 mg/kg) was found, which exceeds the maxi-mum permissible concentration by 1.4 times. Authors consider that high concentration of quicksilver may be a result of short-term local pollution and do not exclude cross-border origin of it. Content of mercury as a part of solid atmospheric precipitation on the Earth’s surface in this area is 37.5 µg/m2, with average values of 10-18 µg/m2. The maximum content of mercury (73.9 µg/m2) was found nearby CHP-3 area. The reason is a high concentration of combustion products in snow cover. The amount of solid atmospheric precipitation in the area of CHP-1 also significantly exceeded the average values, but this did not lead to an increase in the total amount of mercury that reached the surface. The minimum concentration of quicksilver was found in the embankment park area of the city - 3.2 µg/m2.

Distribution characteristics of mercury concentration and estimation of mercury pools in different age groups of Larix gmelinii forests of Daxing'an Mountain

Forests are important sinks of atmospheric mercury. Quantifying mercury pools in forest ecosystem tissues are essential for understanding the global mercury cycle. To reveal the characteristics of Hg concentration and Hg pool distribution in natural forests at different ages, samples from the vegetation layer, organic horizons, coarse wood debris, and mineral soil layers were collected in young forest, middle forest, near-mature forest, and mature forest of Larix gmelinii forests at the Daxing'an Mountain. The results showed that there were differences in the absorption and accumulation of Hg by different tree species and tissues. In Larix gmelinii, the concentration of Hg followed the order of bark > branch > leaf > root > core, whereas in Betula platyphylla, the order was bark > leaf > branch > root > core. The mercury concentration in the organic horizons increased gradually with the decomposition process. There were no obvious regular patterns in the mercury concentrations of each tissue in different age groups Larix gmelinii forests. Furthermore, total biomass mercury pools (overstory, shrub layer, herb layer, moss layer, and coarse woody debris （CWD）) in the young, middle, near-mature, and mature forests of Larix gmelinii forests at Daxing'an Mountain were estimated to be 99.0 μg m-2，207 μg m-2，207 μg m−2 and 194 μg m−2, respectively. On ecosystem scale, total mercury pools were 16.9 mg m−2 (young), 27.5 mg m−2 (middle), 17.0 mg m−2 (near-mature), and 11.8 mg m−2(mature). The mineral soil mercury pool accounts for 94.0%–98.1% of the total ecosystem mercury pool, and its mercury pool proportion gradually decreased with the increase in forest age. These obtained results are quite valuable for further assessing the role of forest ecosystems in the atmospheric mercury cycle and estimating potential mercury emissions from biomass burning during forest wildfires.

Salinity and total suspended solids control mercury speciation in a tidal river: Comparisons with a photochemical mercury model

Daytime volatilization of gaseous elemental mercury (Hg(0)aq) is a significant mechanism for mercury removal from aquatic systems and potentially limits the production and bioaccumulation of methylmercury. Changes in incoming solar radiation (in the ultraviolet range), dissolved organic matter, salinity, and total suspended particles were investigated concurrently with several mercury species (Hg(0)aq, dissolved total mercury (THg), easily reducible mercury (ERM), and mercury associated with total suspended solids (THgTSS)) during daylight hours near the mouth of a hypertidal river. There were no predictable temporal changes observed for Hg(0)aq in unfiltered surface water. Hg(0)aq ranged from 0 to 12 pg L−1, THg ranged from 0 to 492 pg L−1, ERM ranged from 13 to 381 pg L−1, and THgTSS ranged from <1.58 ng g−1 to 261.32 ng g−1. The range of Hg(0)aq predicted by the empirical model was similar to measured ERM concentrations, but it was shown that ERM did not significantly predict in-situ photoreducible Hg(II) (Hg(II)RED). Production of Hg(0)aq appears to largely be suppressed by suspended solids, which limits ultraviolet radiation transmission through surface water. Comparison of these results to an empirical model developed for this site to predict Hg(0)aq indicates that significantly more mercury is available for photoreduction near the mouth of the tidal river, and that Hg(II) will likely photoreduce quickly when TSS levels decrease with ocean mixing.

Mercury concentrations in Antarctic zooplankton with a focus on the krill species, Euphausia superba

The Antarctic is the most isolated region in the world; nevertheless, it has not avoided the negative impact of human activity, including the inflow of toxic mercury (Hg). Hg deposited in the Antarctic marine environment can be bioavailable and accumulate in the food web, reaching elevated concentrations in high-trophic-level biota, especially if methylated. Zooplankton, together with phytoplankton, are critical for the transport of pollutants, including Hg to higher trophic levels. For the Southern Ocean ecosystem, one of the key zooplankton components is the Antarctic krill Euphausia superba, the smaller euphausiid Thysanoessa macrura, and the amphipod Themisto gaudichaudii – a crucial food source for most predatory fish, birds, and mammals. The main goal of this study was to determine the Hg burden, as well as the distribution of different Hg forms, in these dominant Antarctic planktonic crustaceans. The results showed that the highest concentrations of Hg were found in T. gaudichaudii, a typically predatory taxon. Most of the Hg in the tested crustaceans was labile and potentially bioavailable for planktivorous organisms, with the most dangerous methylmercury (MeHg) accounting for an average of 16 % of the total mercury. Elevated Hg concentrations were observed close to the land, which is influenced by the proximity to penguin and pinniped colonies. In areas near the shore, volcanic activity might be a possible cause of the increase in mercury sulfide (HgS) content. The total Hg concentration increased with the trophic position and ontogenetic stage of predation, specific to adult organisms. In contrast, the proportion of MeHg decreased with age, indicating more efficient demethylation or elimination. The Hg magnification kinetics in the study area were relatively high, which may be related to climate-change induced alterations of the Antarctic ecosystem: additional food sources and reshaped trophic structure.

Estimation of smokers' exposure to mercury from combustible tobacco products, based on the approach used in food consumers’ exposure estimation

Smoking has been known to mankind for centuries, but it is only in recent decades that much attention has been paid to the harmfulness of this habit. Mercury inhalation is particularly dangerous in this respect and smoking creates extremely favorable conditions for the emission and targeted delivery of this element into the lungs. Despite this fact, a lack of a clear method for estimating the exposure of tobacco consumers to mercury was identified. This work shows justification to transfer the approach of estimating food product consumers' exposure to estimate the exposure of combustible tobacco product consumers to this element. In addition, it was noted that researchers' attention is mainly focused on cigarettes, while the tobacco market has a wide range of combustible products. Therefore, in this work, the mercury content of cigars (8.45 ± 0.18–41.02 ± 0.20 μg/kg), pipe tobaccos (8.03 ± 0.52–25.48 ± 0.50 μg/kg), bidis (14.93 ± 0.47–31.79 ± 0.26 μg/kg) and cigarette tobaccos (14.22 ± 0.71–34.5 ± 1.4 μg/kg) was analyzed. This study demonstrates that smoking can contribute significant total mercury exposure to consumers', although it is unlikely to cause mercury poisoning regardless of other exposure sources.

Associations between total mercury, trace minerals, and blood health markers in Northwest Atlantic white sharks (Carcharodon carcharias)

The ecology and life-histories of white sharks make this species susceptible to mercury bioaccumulation; however, the health consequences of mercury exposure are understudied. We measured muscle and plasma total mercury (THg), health markers, and trace minerals in Northwest Atlantic white sharks. THg in muscle tissue averaged 10.0 mg/kg dry weight, while THg in blood plasma averaged 533 μg/L. THg levels in plasma and muscle were positively correlated with shark precaudal length (153–419 cm), and THg was bioaccumulated proportionally in muscle and plasma. Nine sharks had selenium:mercury molar ratios in blood plasma >1.0, indicating that for certain individuals the potential protective effects of the trace mineral were diminished, whereas excess selenium may have protected other individuals. No relationships between plasma THg and any trace minerals or health markers were identified. Thus, we found no evidence of negative effects of Hg bioaccumulation, even in sharks with very high THg.

Sedimentary records of contaminant inputs in Frobisher Bay, Nunavut

Contaminants, such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), heavy metals, and per and polyfluoroalkyl substances (PFASs), primarily reach the Arctic through long-range atmospheric and oceanic transport. However, local sources within the Arctic also contribute to the levels observed in the environment, including legacy sources and new sources that arise from activities associated with increasing commercial and industrial development. The City of Iqaluit in Frobisher Bay, Nunavut (Canada), has seen rapid population growth and associated development during recent decades yet remains a site of interest for ocean protection, where Inuit continue to harvest country food. In the present study, seven dated marine sediment cores collected in Koojesse Inlet near Iqaluit, and from sites in inner and outer Frobisher Bay, respectively, were analyzed for total mercury (THg), major and trace elements, PAHs, PCBs, and PFASs. The sedimentary record in Koojesse Inlet shows a period of Aroclor 1260-like PCB input concurrent with military site presence in the 1950–60s, followed by decades of input of pyrogenic PAHs, averaging about ten times background levels. Near-surface sediments in Koojesse Inlet also show evidence of transient local-source inputs of THg and PFASs, and recycling or continued slow release of PCBs from legacy land-based sources. Differences in PFAS congener composition clearly distinguish the local sources from long-range transport. Outside Koojesse Inlet but still in inner Frobisher Bay, 9.2 km from Iqaluit, sediments showed evidence of both local source (PCB) and long-range transport. In outer Frobisher Bay, an up-core increase in THg and PFASs in sediments may be explained by ongoing inputs of these contaminants from long-range transport. The context for ocean protection and country food harvesting in this region of the Arctic clearly involves both local sources and long-range transport, with past human activities leaving a long legacy insofar as levels of persistent organic pollutants are concerned.

A simplified approach to determine the expiration date of certified reference material based on the results of monitoring long-term stability

All components of the quality assurance (QA) system for measurement results depend heavily on certified reference materials (CRMs). There is a need for a comprehensive discussion of the stability study using the CRM statistical method. Monitoring involves periodic sampling and analysis of the CRM at predetermined intervals to continuously monitor stability without compromising its integrity. The obtained stability data is then subjected to statistical analysis, considering factors such as trends, variability, and acceptable limits. In this study, we propose a simplified approach as a linear trend to determine the expiration date of CRM. A case study is conducted using the application of the mentioned statistical approaches according to ISO GUIDE 35:2017 with the inclusion of a linear trend for four MODAS CRMs based on the total mercury (THg) content, which all met the positive criteria for each test and CRM. The proposed approach may be helpful when the requirements stated in section B.4.2 (NOTE 3) are not met of the ISO GUIDE 35:2017. Although the shelf-life is an estimated value, it is, therefore, possible to apply simplifications in the course of its determination. The linear trend analysis would serve an ideal role while accessing the long-term stability study of the CRMs.

Resveratrol alleviates perinatal methylmercury-induced neurobehavioral impairments by modulating the gut microbiota composition and neurotransmitter disturbances.

Methylmercury (MeHg), a potent neurotoxic substance, causes adverse health outcomes by modulating metabolites through altered gut microbiota patterns. Among the many metabolites, neurotransmitters play a particularly important role in the nervous system and behavior. Resveratrol (RSV) has been investigated as an antiaging, antioxidant, anti-inflammatory, and neuroprotective agent. The current study evaluated that RSV is protective of neurodevelopmental toxicity induced by MeHg and further explored the underlying mechanisms. Sprague-Dawley rats were treated with 1.2 mg/kg/d of MeHg, and the effects were evaluated after supplementation with RSV (20 mg/kg/d). The results indicated that MeHg had adverse effects on early neurodevelopmental indicators in the experimental group offspring as compared to control pups. Interestingly, RSV significantly improved the MeHg-induced delays in the neurobehavioral reflexes and reduced the total mercury (THg) concentration in the colons of the offspring rats. In agreement, RSV administration improved the gut microbiota diversity and structure by increasing the abundance of probiotics and upregulating the expression of tight junction proteins. It also ameliorated the MeHg-induced abnormalities in the expression profiles of neurotransmitters. Furthermore, eight key bacteria that were strongly linked with the neurotransmitters and neuroreflex parameters were identified. Taken together, these results demonstrate that RSV treatment effectively reduces the occurrence of neurodevelopmental toxicity caused by perinatal MeHg exposure by modulating the intestinal flora and neurotransmitter metabolism. These findings provide a new therapeutic approach for treating MeHg-induced neurotoxicity. The cover image is based on the Research Article Resveratrol alleviates perinatal methylmercury-induced neurobehavioral impairments by modulating the gut microbiota composition and neurotransmitter disturbances by Fang Chen et al., https://doi.org/10.1002/tox.23973.

Methylmercury content in soil and litter from the Amazonian rainforest and its potential fate during forest fires

Methylmercury in soils and vegetation from the Amazonian rainforest is still poorly studied. Hence, the aim of this work was to determine the total mercury [THg] and methylmercury [MeHg] concentrations in litter and surface soil, MeHg deposition via litterfall, and the MeHg fate during a forest fire in the Amazonian rainforest. Sampling of litter, soil (0–1, 1–2, and 2–5 cm), and ash was carried out before (BB) and after (AB) a prescribed forest fire. The results showed a low [THg] (34 ± 8 ng g-1) and [MeHg] (0.16 ± 0.03 ng g-1) value in litter, with a correspondingly low estimate of the MeHg litterfall flux (0.13 ± 0.03 μgm-2yr-1) which has been probably underestimated due to potential losses during the field experiment. In ashes, [THg] and [MeHg] values were 23 ± 8 ng g-1and 0.11 ± 0.04 ng g-1, respectively. Although a significant part of Hg contained in the biomass was lost during the fire, the [MeHg]/[THg] ratio was not affected by it and was the same in litterfall and ash (∼0.5%). In soil, the average [THg] BB value was 149 ± 12 ng g-1in the three layers and [MeHg] was between 0.8 and 1.0 ng g-1. The forest fire only affected the superficial soil, with a significant decrease of [THg] and [MeHg] in the 0-1 cm layer. Similarly, the decrease of the [MeHg]/[THg] ratio in the surface soil layer suggested that MeHg was more readily emitted or degraded than the other Hg species present.

High levels of mercury contamination in a necrophage dung beetle of the Amazon rainforest (Scarabaeidae: Scarabaeinae)

AbstractThis study represents the first evidence of mercury contamination in the family Scarabaeidae, with a close focus on Coprophanaeus lancifer, the largest copro‐necrophagous beetle in South America. This work shows the repartition of total mercury (THg) in the insect body and lays the groundwork for additional future studies.Abstract in Spanish is available with online material.

Atmospheric mercury speciation and concentration at the urban and industrial sites in Taiwan over a three-year period

Mercury (Hg) is a toxic metal known to be detrimental to human health and wildlife survival due to its serious toxicity to the central nervous system. In this study, measurements of atmospheric mercury in Taiwan over three years suggested significantly higher total Hg concentrations (p < 0.001) during the dry season compared with the wet season for both urban and industrial sites, indicating that precipitation played a role through scavenging Hg. Total gaseous mercury (TGM) was the main component in air accounting for >90% of the total Hg, which included particulate mercury (Hgp). Furthermore, extreme Hg concentrations were observed at sites near cement works (TGM: 18 ng m−3; Hgp: 913 pg m−3) and iron-steel plants (TGM: 24.3 ng m−3; Hgp: 871 pg m−3), indicating a strong role for these two stationary emission sources to Hg concentrations in ambient air. This study contributes to improved understanding of atmospheric mercury speciation and concentrations near iron-steel plants and cement works.

New insight into biomagnification factor of mercury based on food web structure using stable isotopes of amino acids

Although many attempts have been carried out to elaborate trophic magnification factor (TMF) and biomagnification factor (BMF), such as normalizing the concentration of pollutants and averaging diet sources, the uncertainty of the indexes still need to be improved to assess the bioaccumulation of pollutants. This study first suggests an improved BMF (i.e., BMF′) applied to mercury bioaccumulation in freshwater fish from four sites before and after rainfall. The diet source and TP of each fish were identified using nitrogen stable isotope of amino acids (δ15NAAs) combined with bulk carbon stable isotope (δ13C). The BMF′ was calculated normalizing with TP and diet contributions derived from MixSIAR. The BMF′ values (1.3–27.2 and 1.2–27.8), which are representative of the entire food web, were generally higher than TMF (1.5–13.9 and 1.5–14.5) for both total mercury and methyl mercury, respectively. The BMF′ implying actual mercury transfer pathway is more reliable index than relatively underestimated TMF for risk assessment. The ecological approach for BMF calculations provides novel insight into the behavior and trophic transfer of pollutants like mercury.

Relationship of mercury and selenium in ocean fish frequently consumed in the Seychelles: A comparison to levels in ocean fish consumed in the US

We characterized mercury and selenium in the fish consumed in the Seychelles Islands to determine if their levels are similar to fish consumed in the US. A secondary aim was to examine whether fish weight and species predict mercury and selenium in fish consumed in the Seychelles. We measured total mercury (THg) and selenium (Se) content of 10 samples from each of the 19 most frequently consumed fish species in Seychelles and for each calculated the Se:Hg molar ratios and the Selenium Health Benefit Value Index (HBV Se). Linear regression models examined associations with weight and species. Average MeHg levels in fish ranged from less than 0.01 ppm (streamlined spinefoot) to 0.7 ppm (bludger trevally) with an overall mean of 0.21 ± 0.23 ppm. Average Se levels ranged from 0.34 ppm (blue-barred parrot fish) to 0.93 ppm (blue-lined large-eye bream) with a mean of 0.54 ± 0.23 ppm. All fish species had a mean Se:Hg molar ratio > 1 and positive mean HBV Se index values. Weight was strongly predictive of MeHg and Se:Hg molar ratio, both across and within most species, but was less predictive of Se and HBV Se. Our study demonstrated that fish consumed in Seychelles have mercury and selenium content similar to that of fish consumed in the US. Fish in both countries have favorable positive values for Se:Hg molar ratios and HBV Se indexes. Because mercury and selenium concentrations in fish are similar to those in the US but fish consumption is substantially higher in Seychelles, the Seychellois make an ideal population in which to determine if there are adverse effects of prenatal, postnatal, and lifetime low dose MeHg exposure from fish consumption.

Contaminant biomonitoring augmented with a qPCR array indicates hepatic mRNA gene expression effects in wild-collected seabird embryos

Birds can bioaccumulate persistent contaminants, and maternal transfer to eggs may expose embryos to concentrations sufficient to cause adverse effects during sensitive early-life stages. However, using tissue residue concentrations alone to infer whether contaminant effects are occurring suffers from uncertainty, and efficient, sensitive biomarkers remain limited in wildlife. We studied relationships between whole embryo contaminant concentrations (total mercury, organochlorine pesticides, perfluoroalkyl substances, polychlorinated biphenyls, and halogenated flame retardants) together with mRNA expression in embryonic liver tissue from a Pacific Ocean seabird, the rhinoceros auklet (Cerorhinca monocerata). Fresh eggs were collected, incubated under controlled conditions, and from the pre-hatch embryo, hepatic RNA was extracted for qPCR array analysis to measure gene expression (2−∆Cq), while the remaining embryo was analyzed for contaminant residues. Contaminant and gene expression data were assessed with a combination of multivariate approaches and linear models. Results indicated correlations between embryonic total mercury and several genes such as sepp1, which encodes selenoprotein P. Correlation between the biotransformation gene cyp1a4 and the C7 perfluoroalkyl carboxylic acid PFHpA was also evident. This study demonstrates that egg collection from free-living populations for contaminant biomonitoring programs can relate chemical residues to in ovo mRNA gene expression effects in embryo hepatic tissue.

Small mammals as a bioindicator of mercury in a biodiversity hotspot – The Hengduan Mountains, China

Due to toxicities, capacities for long-range transportation, bioaccumulation, and biomagnification, mercury (Hg) presents a unique concern to wildlife in remote ecosystems, including “the roof of the world”. Large carnivorous predators are thought to be exposed to elevated Hg due to their high trophic positions, but the direct assessment for Hg contamination is a challenge. Given the poorly understood Hg exposure in these carnivores, establishing a reliable and straightforward assessment would be essential to identify targeted species at Hg exposure risk for effective conservation, particularly in fragile biodiversity hotspots. Small mammals are abundant and serve as prey for large top predators. Combined with local observations, we provided an assessment to estimate the daily Hg exposure via consumption of small mammals for large carnivorous mammals recorded in the Hengduan Mountains, a world biodiversity hotspot, China. Within an altitude span from 2043 to 4251 m a.s.l., the average topsoil total mercury concentration (hereafter [THg]) was 44.65 ± 25.80 μg/kg (mean ± sd; 10.54 – 135.15 μg/kg, n = 41), while the hair [THg] in small mammals was 104.66 ± 91.96 μg/kg (mean ± sd; 7.73 to 385.70 μg/kg, n = 13). Furthermore, the daily intake of Hg was calculated among the 22 investigated/historical-recorded carnivore mammals belonging to 5 families. We found a large variance in daily intake of Hg via small mammals: Felidae (median: 205.93 μg/day) > Ursidae (135.02 μg/day) > Canidae (92.92 μg/day) > Viverridae (19.88 μg/day) > Mustelidae (7.18 μg/day). Specifically, Tiger Panthera tigris was found with the highest Hg daily intake (1701.39 μg/day) via consuming small mammals, while species belonging to Mustelidae generally have low Hg daily intake (<3 μg/day). This study provides a feasible approach to identifying species at environmental Hg risk in this fragile remote high-elevation region. The limitations and future improvements were discussed.