Mercury Contamination Research Articles

Mercury exposure in riverine populations of Terra do Meio Extractive Reserves in the Xingu basin, Amazon, Brazil.

Amazon is a hotspot for mercury (Hg) contamination and Terra do Meio region, despite its protected status for sustainable use, has never been monitored for this element. Looking to address this gap, this study aimed to quantify capillary Hg concentration in riverine populations of Terra do Meio (Xingu Basin, Central Amazon, Brazil) and associated factors with high Hg levels (90 percentile). Hair samples from 182 individuals from Iriri, Riozinho do Anfrísio and Xingu Extractive Reserves (RESEX), aged between 18 and 70 years old, were collected to measure total mercury levels (HgT), and socioeconomic, demographic, and clinical-epidemiological data were annotated. Overall, high levels of Hg were observed (mean 4.985 µg/g, median 3.531µg/g) with significant differences between localities. Among the factors related to high capillary Hg levels, male gender, smoking habit, work in agriculture, livestock or extractivism, and residence in Iriri and Riozinho do Anfrísio RESEX were highlighted. A high prevalence of symptoms related to Hg intoxication, including anxiety, memory deficit, and lower limb problems, was observed. Overall, the results reveal that communities in these RESEXs are exposed to Hg and appear to be suffering from chronic health effects. Considering the increased anthropogenic alterations observed recently in the Amazon region and the subsequent amplified environmental bioavailability of Hg, further studies and mitigating actions are critical. This includes better surveillance of illegal anthropic activities and provision of ongoing education on this matter and incentives for dietary adaptations.

Mercury distribution and contamination in the soils of the Mitrovica region, Republic of Kosovo

The study was carried out to define the distribution of mercury in surface soils in the Mitrovica region, Republic of Kosovo and to assess the level and extent of contamination. A total of 156 soil samples were collected from a depth of 5 cm at each grid point of 1.4 × 1.4 km in an area of 301.5 km2. The mercury content was found to be between 0.02 mg/kg and 11.16 mg/kg. The average Hg content (0.49 mg/kg) exceeded the mean content in European (0.037 mg/kg) and world (0.06 mg/kg) soils by 13.2 and 8.2 times, respectively. From the calculated enrichment factors (EF) and the geo-accumulation index (I-geo), as well as from the distribution map of Hg content, it is evident that the soils of the study area are highly contaminated with mercury, with extremely high enrichment of Hg in the soils of Zone I, which was classified as the most contaminated zone with Hg and other potentially toxic elements in the study area as well as in the towns of Zveçan and Mitrovica. The higher Hg content is of anthropogenic origin, mainly due to lead and zinc mining and metallurgical activities in the study area. The mercury levels were also found to exceed the New Dutch List target value (0.3 mg/kg) in 90 km2 of the study area.

Selenium–phosphorus modified biochar reduces mercury methylation and bioavailability in agricultural soil

Biochar is a frequently employed for solidifying and stabilizing mercury (Hg) contamination in soil. However, it often results in an elevated presence of soil methylmercury (MeHg), which introduces new environmental risks. Consequently, there is a necessity for developing a safer modified biochar for use in Hg-contaminated soil. This study employed sodium selenite (at a safe dosage for soil) and hydroxyapatite to modify straw biochar (BC) based on the interaction between selenium (Se) and phosphorus (P). This process led to the formation of Se-modified biochar (Se-BC), P-modified biochar (P-BC), and Se and P co-modified biochar (Se-P-BC). Additionally, solvent adsorption experiments and pot experiments (BC/soil mass ratio: 0.5 %) were conducted to investigate the impacts of these soil amendments on soil Hg methylation and bioavailability. Se and P co-modification substantially increased the surface area, pore volume, and Hg adsorption capacity of BC. BC treatment increased the simulated gastric acid-soluble Hg, organo-chelated Hg, and MeHg in the soil. Conversely, Se-P-BC significantly reduced these forms of Hg in the soil, indicating that Se-P-BC can transform soil Hg into less bioavailable states. Among the different biochar treatments, Se-P-BC exhibited the most pronounced reductions in soil MeHg, total Hg, and MeHg in water spinach, achieving reductions of 63 %, 71 %, and 70 %, respectively. The co-modification of Se and P displayed a synergistic reduction effect in managing soil Hg pollution, which is associated with the increase of available Se in the soil due to phosphorus addition. The significantly reduced dissolved organic carbon and the abnormally high SO42− concentration in the soil of Se-P-BC treatment also inhibited Hg methylation and bioavailability in the soil. In summary, Se-P-BC substantially increased reduction percentage in plant Hg content while mitigating the risk of secondary pollution arising from elevated soil MeHg.

Indications that fishers perceive socio-environmental problems related to hydroelectric plants in the Tocantins river, Brazil

Hydroelectric dams (HEDs) cause significant socio-environmental damage such as reduced fish diversity, population displacement and health problems. The fishers have extensive local ecological knowledge that can be used to improve understanding of the impacts of HEDs. Therefore, the objective of this study was to verify and evaluate the perceptions of fishers about the impacts caused by the HEDs in the Tocantins River. For this, 25 fishers were interviewed using a questionnaire with 22 questions. Data analyses were performed considering descriptive analysis of the responses. There was convergence in the responses of fishers who perceived the decrease in fish diversity after the construction of the HEDs, including fish of commercial interest, which is linked to a decrease in income and decreased food security for these families. In addition, the fishers noted symptoms that may be a consequence of mercury contamination, and diarrhea as a possible consequence of decreased water quality. Despite all these socio-environmental losses, the fishers report a lack of prior consultation, and low representativeness and transparency in the decision-making process that preceded the construction of HEDs. In general, the fishers perceived themselves as being strongly affected from the socio-environmental point of view and do not cite any benefits offered to the community from these projects.

Catchment land use effect on mercury concentrations in lake sediments: A high-resolution study of Qinghai Lake

Mercury (Hg) contamination in aquatic environments presents a significant ecological and human health concern. This study explored the relationship between catchment land use and Hg concentrations within Qinghai Lake sediment, the largest lake in China, situated on the Qinghai-Tibet plateau. The study entailed detailed mapping of Hg sediment concentrations and a subsequent environmental risk assessment. Considering the complex nature of the plateau landform and surface vegetation, the study area was delineated at a 100 km radius centered on Qinghai Lake, which was divided into 30 sectors to quantify relationships between land use and the sediment Hg concentration. The results revealed a mean sediment Hg concentration of 29.91 μg/kg, which was elevated above the background level. Kendall's correlation analysis revealed significant but weak associations between sediment Hg concentrations and three land use types: grassland (rangeland and trees) (rs = 0.27, p < 0.05), crops (rs = −0.37, p < 0.05), and bare ground (rs = −0.25, p < 0.1), suggesting that growing areas of grassland correlated with higher Hg levels in the lake sediment, in contrast to bare ground or crops area, which correlated with lower Hg concentrations. Multiple linear regression models also observed weak negative relationships between bare ground and crops with sediment Hg concentration. This research methodology enhances our understanding of the impact of land use on Hg accumulation in lake sediments and underscores the need for integrated watershed management strategies to mitigate Hg pollution in Qinghai Lake.

Mercury distribution, exposure and risk in Poyang Lake and vicinity, China

Mercury (Hg), especially methylmercury (MeHg), which is highly neurotoxic, is a global pollutant that can affect human health because of its accumulation in aquatic products. Poyang Lake, an inland lake in China, has been significantly affected by human activity, yet there is limited understanding of local mercury contamination and potential exposure pathways to humans. In this study, we explored the risks of mercury exposure by sampling sediments, plants, and aquatic organisms in the lake and surrounding areas and analyzing total Hg (THg) and MeHg levels. Sediment sampling was conducted at the main lake, rivers, rice paddies, and fishponds. Two dominant species of plants and 15 species of aquatic organisms were sampled and analyzed. We assessed the characteristics of mercury in sediments using the geo-accumulation index (Igeo), mercury exposure using the biomagnification factor (BMF) and biota sediment accumulation factor (BSAF), and risks using thresholds for adverse effects. The highest THg concentrations (137.04 ± 44.3 ng g−1 dw) were detected in the main lake sediments, whereas the highest MeHg concentrations (0.47 ± 0.6 ng g−1 dw) were detected in fishpond sediments. Mercury accumulation in the main lake sediments could be assessed as contaminated (Igeo > 0: 81.6%). Yellow catfish had the highest mercury concentration (THg 770.69 ± 199.7 ng g−1 dw; MeHg 741.93 ± 168.8 ng g−1 dw). Piscivores were adversely affected by carnivorous fish (50.8%), but all fish concentrations did not exceed the food safety standards recommend by China and the WHO. The mercury exposure results revealed significant Hg biomagnification and enrichment (BMF >1: 94.55%; BSAFmax = 1218). Long-term monitoring of aquatic organisms is warranted.

Efficient selective uptake of Hg(Ⅱ) using a porous organic polymer rich in N and S atoms

The escalating issue of mercury (II) ions (Hg2+) pollution in water, primarily due to human activities, poses a significant environmental and health risk. Addressing the urgent need for efficient Hg2+ removal, this study introduces a novel porous organic polymer (TpTHU) synthesized through Schiff base condensation of thiourea (THU) and 1,3,5-Triformylphloroglucinol (Tp). TpTHU, enriched with sulfur and nitrogen, facilitates soft–soft interaction with Hg2+, offering a potent solution for mercury contamination. Our experimental results demonstrate TpTHU's remarkable adsorption capacity for Hg2+, reaching 1250 mg/g, attributed to its dense complexation sites. The adsorption behavior aligns well with the Brouers-Sotolongo model. Notably, TpTHU achieves 99.25% mercury removal within 120 min over a broad pH range (4 to 10), underscoring its rapid action. Additionally, in fixed-bed column experiments, TpTHU effectively lowers Hg2+ concentrations in industrial wastewater from 10.0 mg/L to below 5 μg/L, surpassing industrial emission standards. Through XPS analysis and density functional theory calculations, we elucidate the adsorption mechanism, affirming TpTHU's efficiency. With its straightforward synthesis, high efficacy, and excellent reusability, TpTHU emerges as a promising candidate for mitigating Hg2+ pollution in industrial wastewater.

Comparative analysis between mercury levels in fish tissues evaluated using direct mercury analyzer and inductively plasma-coupled mass spectrometer

Recent ecotoxicological studies have indicated mercury (Hg) contamination in aquatic ecosystems in the Amazon Basin. Although Hg contamination can be associated with small-scale gold mining, the soils of the Amazon region have naturally high Hg concentrations, and can be transported to aquatic ecosystems via deforestation and mining activities. Biomagnification of Hg can pose risks to the local human population; therefore, its concentration in fish tissues must be monitored consistently. Fast and sensitive Hg determination is required for continuously monitoring ecosystems impacted by mineral exploration. The direct mercury analyzer (DMA-80) is widely used for determining total Hg levels in tissue samples; it is fast and cost-effective, without requiring sample preparation. Here, we determined the sensitivity and specificity of Hg detection accomplished using DMA-80, and whether these results are reliable compared to those obtained using Inductively Coupled Plasma Mass Spectrometer (ICP-MS), which is the gold standard. We obtained 106 paired dried samples of muscle tissue from fish species occupying different trophic levels in the Lower Amazon region, and analyzed them using both equipment (DMA-80 and ICP-MS). The results obtained using DMA-80 had an overall Hg mean of 1.90 ± 0.18 mg/kg which was higher (p < 0.05) than the mean of those obtained using ICP-MS (1.55 ± 0.13 mg/kg). Linear regression analysis comparing the Hg levels obtained using both devices was within the 95% prediction interval, and a high coefficient of correlation showed agreement between the devices (r = 0.979; 0.069 to 0.986, 95% CI). Bland-Altman analysis showed that DMA-80 had a positive bias of 6.5% in relation to ICP-MS, which is more evident in samples with high Hg concentrations. DMA-80 was efficient in determining whether the Hg levels exceeded the maximum allowed levels required by the European Union, USA, and Brazil, showing a specificity and sensitivity of above 95%.

Pollution simulation of heavy metal in saturated porous media using CFD

Visualizing contaminant transport can play a significant role in better understanding the fate of contaminants in soil. The present study aimed to evaluate contamination of aluminium and mercury in the soil through the use of computational fluid dynamics (CFD) to obtain an estimate of degraded zones. A leak from a generic stabilization pond measuring 40 m (length) and 20 m (width) was developed for the simulations. The simulations were carried out for a period of 10 years with different leak speeds, water inlet flow rates and different values of aluminum and mercury volume fractions. All governing equations was solved with the transient mode. The flow characterized as laminar, and the multiphase model was employed through the Mixture method. The time required for contamination to reach its maximum value was directly influenced by the change in speed values. The concentration of the pollutant increases as the water inlet and leakage speeds increase, however, it reduces the time needed to reach the highest pollutant value, indicating that the degree of pollution of the porous medium was greater. The study shows that contamination can be seen as a potential contaminant source for groundwater.

Assessment of mercury accumulation in various tissues of rice plant (Oryza sativa L.) from a Ramsar site in India

Dietary exposure to mercury through rice consumption is an issue of solemn global concern. The favourable bio-geochemical environment of paddy fields often makes them potential mercury cycling hotspots. India is one of the largest producers and consumers of rice globally. To date, studies focusing on mercury bioaccumulation in rice during the different stages of its growth cycle have not been studied in Indian agro-ecosystems.This inturn resulted in a knowledge gap in the global mercury assessment. Being a party to the Minamata Convention, there is an urgent need to unravel the scenario of mercury contamination in rice, one of the staple food crops across the world. In the present study, total mercury (THg) in the rhizosphere soil as well as its accumulation in different tissues of the rice plant were examined by a field investigation in Kuttanad – a unique Ramsar site in Kerala, India. For the purpose of the study five permanent plots were selected and monitored for the entire rice-growing season (from the 30th to the 120th day). Direct Mercury Analyzer (DMA – 80, Milestone, USA) was used for analyzing THg in rhizosphere soil and plant tissues. Mercury concentration in soils varied from 0.037 mg/kg to 0.117 mg/kg with a mean concentration of 0.088 mg/kg. The THg accumulation pattern in plant tissues followed the order: root > leaf > grain > husk > stem. The mean THg concentration in rice grains was 0.22 mg/kg. The low values for bioaccumulation factor (0.616) and translocation factor (0.425) revealed that a major portion of mercury accumulated by the plant is stored in the roots.

Real-time optical detection of mercury contamination in drinking water using an amphiphilic recognition probe at liquid crystal/aqueous interfaces.

Mercury contamination is a global environmental issue due to its toxicity and persistence in ecosystems. It poses a particular risk in aquatic systems, where it bioaccumulates and biomagnifies, leading to serious health impacts on humans. Therefore, effective detection technologies for mercuric ions in natural water resources are highly desirable. However, most existing detection methods are time-consuming, require complicated sample pre-treatment, and rely on expensive equipment, which hinders their widespread use in real-time detection. Here, we present a convenient, rapid, portable, user-friendly, and cost-effective sensing system for detecting Hg2+ ion contamination in water. This system utilizes a highly selective, amphiphilic, and structurally simple molecular probe, N-dodecylamine-di-thiocarbamate (DDC). DDC molecules align at the interface between the liquid crystal (LC) and water, inducing a homeotropic LC orientation. In water samples contaminated with Hg2+, a bright optical texture is observed, indicating the alignment of the 5CB LC in a planar manner at the LC/aqueous boundary. The minimum detectable concentration (LOD) for Hg2+ ions is 5.0 μM in distilled water, with a broad detection range from 5.0 μM to 2 mM. The sensor selectively detects Hg2+ ions over other common interfering metal ions, including Pb2+, Co2+, Ni2+, Cu2+, Cd2+, Zn2+, Cr2+, Mg2+, Na+, K+, and Ca2+. Boolean logic gates, bar graphs, and truth tables are employed to explain the selectivity of this liquid crystal-based sensor. This work demonstrates the significant potential of the sensor for monitoring mercuric ions in natural water resources, offering a promising strategy for controlling mercury pollution.

Assessment of Lead and Mercury Contamination in Amphidromous Goby Larvae (Nike), Water Quality, and Associated Human Health Risks in Bone Estuary, Indonesia

Assessment of Lead and Mercury Contamination in Amphidromous Goby Larvae (Nike), Water Quality, and Associated Human Health Risks in Bone Estuary, Indonesia

Advancements in mercury detection using surface-enhanced Raman spectroscopy (SERS) and ion-imprinted polymers (IIPs): a review.

Mercury (Hg) contamination remains a major environmental concern primarily due to its presence at trace levels, making monitoring the concentration of Hg challenging. Sensitivity and selectivity are significant challenges in the development of mercury sensors. Surface-enhanced Raman spectroscopy (SERS) and ion-imprinted polymers (IIPs) are two distinct analytical methods developed and employed for mercury detection. In this review, we provide an overview of the key aspects of SERS and IIP methodologies, focusing on the recent advances in sensitivity and selectivity for mercury detection. By examining the critical parameters and challenges commonly encountered in this area of research, as reported in the literature, we present a set of recommendations. These recommendations cover solid and colloidal SERS substrates, appropriate Raman reporter/probe molecules, and customization of IIPs for mercury sensing and removal. Furthermore, we provide a perspective on the potential integration of SERS with IIPs to achieve enhanced sensitivity and selectivity in mercury detection. Our aim is to foster the establishment of a SERS-IIP hybrid method as a robust analytical tool for mercury detection across diverse fields.

Efficiency of Sea Pandan Leaves (Pandanus tectorius) in the Biosorption of Mercury (Hg) in Coastal Areas

Mercury (Hg) heavy metal pollution is one of the serious problems that can threaten human health and ecosystems. In an effort to reduce mercury contamination, this research uses sea pandanus leaves (pandanus tectorius) as a natural biosorbent. The purpose of this study is to determine the contact time and adsorbing concentration capacity of sea pandanus leaves to mercury ions. One of the steps to reduce mercury contamination is by biosorption. The data obtained were analyzed using J.S.A.P software to determine the real difference test on contact time and adsorption concentration. The results of this study indicate that sea pandanus has a mercury adsorption capacity determined by the optimum contact time in the ratio of 1:100, the best optimum contact time is 60 minutes with an adsorption concentration of 100 ppm by achieving an adsorption of 0.372 mg/g using a mesh size of 120, Comparison of 1:75, the best optimum contact time is 30 minutes with an adsorption concentration of 0.907 mg/g using a mesh size of 120. Sea pandan leaves are proven as a potential biosorbent to remove mercury ions with the application of sea pandan leaves with seawater, which is 95% able to absorb heavy metals in polluted seawater.

Contamination of Mercury (Hg) and Lead (Pb) in Seawater and Sediments in Coastal waters of Ohoitel Village, Southeast Maluku District

Along with the increasing population in the coastal area of Ohoitel Village, it triggers the level of community settlement with an increase in anthropogenic activities. This study aims to determine the concentration of heavy metal mercury (Hg) and lead (Pb) dissolved in water and accumulated in sediments. Measurement of heavy metal levels using Atomic Absorption Spectrophometer (AAS). The results of the analyis og Hg content obtained in seawater at station I was 0.00100 ± 0.00007 mg/l, station II was 0.00096 ± 0.00026 mg/l and station III was 0.00101 ± 0.000026 mg/l. The results of Hg levels obtained in sediment at station I amounted to 0.08557 ± 0.0003 mg/l, station II amounted to 0.07761 ± 0.0004 mg/l and station III amounted to 0.08733 ± 0.0004 mg/l. The results of the analysis of Pb content in seawater at station I was 0.00050 ± 0.000003 mg/l, station II was 0.000047 ± 0.000003 mg/l and station III was 0.000038 ± 0.000005 mg/l. Based on the results obtained, it shows that it is still below the quality standard threshold that refers to PP RI No 22 0f 2021 for water and ANZECC 2000 for heavy metal Hg in sediment and USEPA for heavy metal Pb in sediment

Bioaccumulation of mercury in Lake Michigan painted turtles (Chrysemys picta).

Mercury (Hg) contamination of aquatic environments can lead to bioaccumulation in organisms, but most previous work has focused on fish and not on semi-aquatic reptiles such as turtles that traverse both terrestrial and aquatic habitats. Here, we analyzed total Hg (THg) concentrations in 30 painted turtles (Chrysemys picta) collected from Lake Michigan (USA) coastal wetlands in 2013 to determine if (1) turtles bioaccumulated THg from the environment, (2) concentrations differed between turtle liver and muscle tissue, and (3) tissue concentrations were related to environmental concentrations (e.g., sediment THg). All individual turtles had detectable THg concentrations in both liver and muscle tissue. On average, THg concentrations were over three times higher in liver tissue compared to muscle tissue. We found a positive linear relationship between muscle THg concentrations and turtle body mass, a proxy for age, suggesting bioaccumulation in this species. Neither liver nor muscle THg concentrations followed the sediment contaminant gradient in the wetlands. Despite this, location was a strong predictor of tissue concentration in a linear model suggesting that other site-specific characteristics may be important. Overall, our results demonstrate that painted turtles accumulate mercury in liver and muscle tissues at different rates, which may be constrained by local conditions. Further research is needed to better understand the relationship between environmental mercury concentrations and body burdens in animals like turtles that traverse habitats. In addition, long-lived turtles could be incorporated into pollution monitoring programs to provide a more holistic picture of food web contamination and ecosystem health.

Poison in the nursery: Mercury contamination in the tadpole-rearing sites of an Amazonian frog

Artisanal and small-scale gold mining (ASGM) has become a major threat for Neotropical forests. This technique for obtaining gold is a substantial driver of small-scale deforestation and the largest contributor of Hg emissions to both the atmosphere and freshwater systems globally. Previous studies have demonstrated the impacts of Hg accumulation on various aquatic ecosystems and organisms. However, its consequences in other, more discrete systems such as phytotelmata (water-holding plant structures), and the organisms therein, have so far gone unnoticed. Here, we show high concentrations of Hg (mean ± SD: 1.43 ± 2.19 ppm) in phytotelmata and other small pools, the aquatic microenvironments used by the Neotropical poison frog Dendrobates tinctorius as tadpole-rearing sites. In 17 % of the cases, we detected Hg concentrations above the severe effect level (SEL = 2 ppm) for freshwater sediments. Hg concentrations varied depending on pool characteristics and tended to increase in proximity to known ASGM sites. We did not find an effect of Hg concentration on the number of D. tinctorius tadpoles in a given pool. Tadpoles were found in pools with concentrations of up to 8.68 ppm, suggesting that D. tinctorius fathers do not avoid pools with high Hg levels for tadpole deposition. While further research is needed to determine the potential effects of Hg on tadpole development, we found an intriguing tendency for tadpoles in later developmental stages to have lower body condition when occurring in pools with higher Hg concentrations. Our findings provide evidence of relevant Hg concentrations in the terrestrial water systems used by phytotelm-breeding anurans, and highlight the need of further field and experimental studies investigating the implications of Hg contamination for tadpole development and behaviour and the overall conservation of Amazonian biodiversity.

Assessing mercury contamination in Southern Hemisphere marine ecosystems: The role of penguins as effective bioindicators

Mercury (Hg) is a global pollutant known for its significant bioaccumulation and biomagnification capabilities, posing a particular threat to marine environments. Seabirds have been recognized as effective bioindicators of marine pollution, and, among them, penguins present a unique opportunity to serve as a single taxonomic group (Sphenisciformes) for monitoring Hg across distinct marine ecosystems in the Southern Hemisphere. In this study, we conducted a comprehensive systematic review of Hg concentrations, and performed a meta-analysis that took into account the various sources of uncertainty associated with Hg contamination in penguins. Beyond intrinsic species-specific factors shaping Hg levels, our results showed that the penguin community effectively reflects spatial patterns of Hg bioavailability. We identified geographic Hg hotspots in Australia, the Indian Ocean, and Tierra del Fuego, as well as coldspots in Perú and the South Atlantic. Furthermore, specific penguin species, namely the Southern Rockhopper (Eudyptes chrysocome) and Macaroni penguin (Eudyptes chrysolophus), are highlighted as particularly vulnerable to the toxic effects of Hg. Additionally, we identified knowledge gaps in geographic areas such as the Galápagos Islands, South Africa, and the coast of Chile, as well as in species including Fiordland (Eudyptes pachyrhynchus), Snares (Eudyptes robustus), Erect-crested (Eudyptes sclateri), Royal (Eudyptes schlegeli), Yellow-eyed (Megadyptes antipodes), and Galápagos (Spheniscus mendiculus) penguins. Overall, our study contributes to the growing body of literature emphasizing the role of penguins as bioindicators of Hg pollution, but it also highlights areas where further research and data collection are needed for a more comprehensive understanding of Hg contamination in marine ecosystems in the Southern Hemisphere.

Influence of a hydroelectric dam on fish mercury contamination along the Sinnamary River (French Guiana)

The Petit Saut hydroelectric dam and the upstream and downstream areas of the Sinnamary River in French Guiana (Amazon basin) have been studied from 1993 to 2020. The nearly thirty-years-long study of the monitoring of total mercury concentration in fish and the physicochemical survey of the environment made it possible to demonstrate the impact of the flooding of the forest and the role of the hydroelectric dam on the methylation of mercury. Results show that the physicochemical modifications generated by the construction of the dam led to a significant production of methylmercury (MeHg) in the anoxic part of the reservoir and downstream of the river leading to a strong spatio-temporal impact of the dam. Seven species of fishes are studied and their mercury concentrations vary according to many parameters: fish diet, position in the water column, site, lake oxycline level and time.

Gut microbiome play a crucial role in geographical and interspecies variations in mercury accumulation by fish

Mercury (Hg) contamination in fish has raised global concerns for decades. The Hg biotransformation can be manipulated by gut microbiome and it is found to have a substantial impact on the speciation and final fate of Hg in fish. However, the contribution of intestinal microbiota in geographical and interspecies variations in fish Hg levels has not been thoroughly understood. The present study compared the Hg levels in wild marine fish captured from two distinct regions in South China sea. We observed a quite “ironic” phenomenon that MeHg levels in carnivorous fish from a region with minimal human impacts (Xisha Islands, 92 ± 7.2 ng g−1 FW) were much higher than those from a region with severe human impacts (Daya Bay, 19 ± 0.41 ng g−1 FW). Furthermore, the results showed that gut microbiome determined Hg biotransformation and played a crucial role in the variances in fish Hg levels across different geographical locations and species. The intestinal methylators, rather than demethylators, were more significant in affecting Hg biotransformation in fish. The carnivorous species in Xisha Islands exhibited a higher abundance of intestinal methylators, leading to higher MeHg accumulation. Besides, the gut microbiome could be shaped in response to the elevated Hg levels in these fish, which may benefit their adaptation to Hg toxicity and overall health preservation. However, anthropogenic activities (particularly overfishing) in Daya Bay have severely affected the fish population, disrupting the reciprocal relationships between fish and intestinal microbiota and rendering them more susceptible to pathogenic microbes. Overall, this study provided a comprehensive understanding of the role of gut microbiome in Hg bioaccumulation in fish and offered valuable insights into the co-evolutionary dynamics between fish and gut microbiome in the presence of Hg exposure.