An investigation of mercury sources in the Puyango-Tumbes River: Using stable Hg isotopes to characterize transboundary Hg pollution

Mercury stable isotopes in seabirds in the Ebro Delta (NE Iberian Peninsula): Inter-specific and temporal differences

Mercury (Hg) is a global pollutant, which particularly affects aquatic ecosystems, both marine and freshwater. Top-predators depending on these environments, such as seabirds, are regarded as suitable bioindicators of Hg pollution. In the Ebro Delta (NE Iberian Peninsula), legacy Hg pollution from a chlor-alkali industry operating in Flix and located ca. 100 km upstream of the Ebro River mouth has been impacting the delta environment and the neighboring coastal area. Furthermore, levels of Hg in the biota of the Mediterranean Sea are known to be high compared to other marine areas. In this work we used a Hg stable isotopes approach in feathers to understand the processes leading to different Hg concentrations in three Laridae species breeding in sympatry in the area (Audouin's gull Ichthyaetus audouinii, black-headed gull Chroicocephalus ridibundus, common tern Sterna hirundo). These species have distinct trophic ecologies, exhibiting a differential use of marine resources and freshwater resources (i.e., rice paddies prey). Moreover, for Audouin's gull, in which in the Ebro Delta colony temporal differences in Hg levels were documented previously, we used Hg stable isotopes to understand the impact of anthropogenic activities on Hg levels in the colony over time. Hg stable isotopes differentiated the three Laridae species according to their trophic ecologies. Furthermore, for Audouin's gull we observed temporal variations in Hg isotopic signatures possibly owing to anthropogenic-derived pollution in the Ebro Delta. To the best of our knowledge this is the first time Hg stable isotopes have been reported in seabirds from the NW Mediterranean.

Transitional dynamics from mercury to cyanide-based processing in artisanal and small-scale gold mining: Social, economic, geochemical, and environmental considerations

Artisanal and small-scale gold mining (ASGM) is the leading global source of anthropogenic mercury (Hg) release to the environment. Top-down mercury reduction efforts have had limited results, but a bottom-up embrace of cyanide (CN) processing could eventually displace mercury amalgamation for gold recovery. However, ASGM transitions to cyanidation nearly always include an overlap phase, with mercury amalgamation then cyanidation being used sequentially. This paper uses a transdisciplinary approach that combines natural and social sciences to develop a holistic picture of why mercury and cyanide converge in gold processing and potential impacts that may be worse than either practice in isolation. We show that socio-economic factors drive the comingling of mercury and cyanide practices in ASGM as much or more so than technical factors. The resultant Hg-CN complexes have been implicated in increasing the mobility of mercury, compared to elemental mercury used in Hg-only processing. To support future inquiry, we identify key knowledge gaps including the role of Hg-CN complexes in mercury oxidation, transport, and fate, and possible links to mercury methylation. The global extent and increase of mercury and cyanide processing in ASGM underscores the importance of further research. The immediacy of the problem also demands interim policy responses while research advances, though ultimately, the well-documented struggles of mercury reduction efforts in ASGM temper optimism about policy responses to the mercury-cyanide transition.

Impact of forest fire on the mercury stable isotope composition in litter and soil in the Amazon

Mercury (Hg) emissions from forest fires, especially tropical forests such as the Amazonian forest, were shown to contribute significantly to the atmospheric mercury budget, but new methods are still necessary to improve the traceability and to reduce the great uncertainties related to this emission source. Recent studies have shown that the combustion process can result in Hg stable isotope fractionation that allows tracking coal combustion Hg emissions, as influenced by different factors such as combustion temperature. The main goal of the present study was, therefore, to investigate for the first time the potential of Hg stable isotopes to trace forest fire Hg emissions and pathways. More specifically, small-scale and a large scale prescribed forest fire experiments were conducted in the Brazilian Amazonian forest to study the impact of fire severity on Hg isotopic composition of litter, soil, and ash samples and associated Hg isotope fractionation pathways. In the small-scale experiment, no difference was found in the mercury isotopic composition of the samples collected before and after burning. In contrast, the larger-scale experiment resulted in significant mass dependent fractionation (MDF δ202Hg) in soils and ash suggesting that higher combustion temperature influence Hg isotopic fractionation with the emission of lighter Hg isotopes to the atmosphere and enrichment with heavier Hg in ashes. As for coal combustion, mass independent fractionation was not observed. To our knowledge, these results are the first to highlight the potential of forest fires to cause Hg isotopic fractionation, depending on the fire severity. The results also allowed to establish an isotopic fingerprint for tropical forest fire Hg emissions that corresponds to a mixture of litter and soil Hg isotopic composition (resulting atmospheric δ202Hg, Δ200Hg and Δ199Hg were -1.79 ± 0.24‰, -0.05 ± 0.04‰ and -0.45 ± 0.12‰, respectively).

Enhanced mercury phytoremediation by Pseudomonodictys pantanalensis sp. nov. A73 and Westerdykella aquatica P71

Mercury is a non-essential and toxic metal that induces toxicity in most organisms, but endophytic fungi can develop survival strategies to tolerate and respond to metal contaminants and other environmental stressors. The present study demonstrated the potential of mercury-resistant endophytic fungi in phytoremediation. We examined the functional traits involved in plant growth promotion, phytotoxicity mitigation, and mercury phytoremediation in seven fungi strains. The endophytic isolates synthesized the phytohormone indole-3-acetic acid, secreted siderophores, and solubilized phosphate in vitro. Inoculation of maize (Zea mays) plants with endophytes increased plant growth attributes by up to 76.25%. The endophytic fungi stimulated mercury uptake from the substrate and promoted its accumulation in plant tissues (t test, p < 0.05), preferentially in the roots, which thereby mitigated the impacts of metal phytotoxicity. Westerdykella aquatica P71 and the newly identified species Pseudomonodictys pantanalensis nov. A73 were the isolates that presented the best phytoremediation potential. Assembling and annotation of P. pantanalensis A73 and W. aquatica P71 genomes resulted in genome sizes of 45.7 and 31.8 Mb that encoded 17,774 and 11,240 protein-coding genes, respectively. Some clusters of genes detected were involved in the synthesis of secondary metabolites such as dimethylcoprogen (NRPS) and melanin (T1PKS), which are metal chelators with antioxidant activity; mercury resistance (merA and merR1); oxidative stress (PRX1 and TRX1); and plant growth promotion (trpS and iscU). Therefore, both fungi species are potential tools for the bioremediation of mercury-contaminated soils due to their ability to reduce phytotoxicity and assist phytoremediation.

A synthesis of mercury research in the Southern Hemisphere, part 2: Anthropogenic perturbations

Environmental mercury (Hg) contamination is a global concern requiring action at national scales. Scientific understanding and regulatory policies are underpinned by global extrapolation of Northern Hemisphere Hg data, despite historical, political, and socioeconomic differences between the hemispheres that impact Hg sources and sinks. In this paper, we explore the primary anthropogenic perturbations to Hg emission and mobilization processes that differ between hemispheres and synthesize current understanding of the implications for Hg cycling. In the Southern Hemisphere (SH), lower historical production of Hg and other metals implies lower present-day legacy emissions, but the extent of the difference remains uncertain. More use of fire and higher deforestation rates drive re-mobilization of terrestrial Hg, while also removing vegetation that would otherwise provide a sink for atmospheric Hg. Prevalent Hg use in artisanal and small-scale gold mining is a dominant source of Hg inputs to the environment in tropical regions. Meanwhile, coal-fired power stations continue to be a significant Hg emission source and industrial production of non-ferrous metals is a large and growing contributor. Major uncertainties remain, hindering scientific understanding and effective policy formulation, and we argue for an urgent need to prioritize research activities in under-sampled regions of the SH.

A synthesis of mercury research in the Southern Hemisphere, part 1: Natural processes

Recent studies demonstrate a short 3-6-month atmospheric lifetime for mercury (Hg). This implies Hg emissions are predominantly deposited within the same hemisphere in which they are emitted, thus placing increasing importance on considering Hg sources, sinks and impacts from a hemispheric perspective. In the absence of comprehensive Hg data from the Southern Hemisphere (SH), estimates and inventories for the SH have been drawn from data collected in the NH, with the assumption that the NH data are broadly applicable. In this paper, we centre the uniqueness of the SH in the context of natural biogeochemical Hg cycling, with focus on the midlatitudes and tropics. Due to its uniqueness, Antarctica warrants an exclusive review of its contribution to the biogeochemical cycling of Hg and is therefore excluded from this review. We identify and describe five key natural differences between the hemispheres that affect the biogeochemical cycling of Hg: biome heterogeneity, vegetation type, ocean area, methylation hotspot zones and occurence of volcanic activities. We review the current state of knowledge of SH Hg cycling within the context of each difference, as well as the key gaps that impede our understanding of natural Hg cycling in the SH. The differences demonstrate the limitations in using NH data to infer Hg processes and emissions in the SH.

Mercury migration to surface water from remediated mine waste and impacts of rainfall in a karst area - Evidence from Hg isotopes

Mine waste (MW) in historical mercury (Hg) mining areas continuously emits Hg into local environment, including aquatic ecosystems. Tracing Hg migration process from MW and determining its relative contribution to Hg pollution is critical for understanding the environmental impact of MW remediation. In this study, we combined data of Hg concentration, speciation, and isotope to address this issue in the Wanshan Hg mining area in southwest China. We found that rainfall can elevate Hg concentrations in river water and control the partitioning and transport of Hg in karst fissure zones through changing the hydrological conditions. A consistently large offset of δ²⁰²Hg (1.24‰) was observed between dissolved Hg (DHg) and particulate Hg (PHg) in surface water during the low-flow period (LFP), which may have been related to the relatively stable hydrologic conditions and unique geological background (karst fissure zones) of the karst region (KR). Results from the ternary Hg isotopic mixing model showed that, despite an order of magnitude reduction in Hg concentration and flux in river water after remediation, the remediated MW is still a significant source of Hg pollution to local aquatic ecosystems, accounting for 49.3 ± 11.9% and 37.8 ± 11.8% of river DHg in high flow period (HFP) and LFP, respectively. This study provides new insights into Hg migration and transportation in aquatic ecosystem and pollution source apportionment in Hg polluted area, which can be used for making polices for future remediation actions.

Mercury pollution in Peru: geographic distribution, health hazards, and sustainable removal technologies

Peru is one of the great gold producers worldwide. However, a significant portion of the gold produced in Peru derives from artisanal small-scale gold mining (ASGM) in the Andes and Amazon. In ASGM, gold amalgamation with mercury (Hg) is a critical procedure to refine gold through the formation of Au-Hg alloys. Due to the rudimentary and improvised techniques conducted by small-scale and informal miners, Hg contamination has become of great concern and is strictly associated with ASGM. Multiple studies have evidenced notably high concentrations of Hg in consumable fish species, rivers, sediments, and air in locations where ASGM is one of the main sources of income to local communities and is carried out aggressively. In the present review, we have conducted a systematic search for national and international literature reporting the concentration and distribution of Hg pollution across environmental compartments, biota, and human samples in Peru. The results and data retrieved from the articles were quantitatively and qualitatively analyzed, and the distribution of Hg across environmental compartments was visualized through a geographic information system. Additionally, we reviewed the use of adsorption techniques as alternatives to treat Hg⁰ vapor from the gold shop and smelter flues, one of the main sources of hazardous levels of Hg exposure.

History, Socioeconomic Problems and Environmental Impacts of Gold Mining in the Andean Region of Ecuador

Mining in Ecuadorian territory comprises three stages of Ecuadorian history: pre-Columbian, colonial, and republican times. In its beginnings, this activity did not have regulations or a legal foundation. The first Mining Law dates back to 1830, and it has been modified until the most recent update in 2009. The Andean region consists of 10 provinces, 9 of which have registered gold concessions, the most important of which are Loja, Azuay, and in recent years, Imbabura and Pichincha, which are the provinces with the highest number of reported concessions. The objective of this study focused on analyzing the historical and current situation of Artisanal and Small-scale Mining (ASGM) and the emergence of large-scale (industrial) mining. For the elaboration of this study, different methodological techniques were used, such as literature review, field interviews, and expert judgment validation. The main findings show that the provinces of Loja, Azuay, Imbabura, and Pichincha are the most conflictive areas in the region due to the impacts caused by mining activities. In socio-economic terms, there are conflicts between inhabitants in favor and against these activities and problems associated with human health. In environmental terms, the findings suggest historical contamination of water sources by heavy metals, which has altered the surrounding aquatic and terrestrial systems. Finally, the study concludes that implementing public policies should be promoted to balance socio-economic and environmental aspects in gold mining activities in the Andean region of Ecuador, strengthening the use of new technologies and education to raise awareness of the serious effects of mining activities.

Using Zn isotopes to trace Zn sources and migration pathways in paddy soils around mining area

Paddy soils around mining areas suffer from the great threat of heavy metal pollution. The traditional source-tracing methods based on metal concentrations limit our ability to quantify the sources of heavy metals and trace their transport processes to paddy soils. In this study, Zn isotope compositions of paddy soils in Dabaoshan mine area, a typical sulfide deposit in southern China, have been systematically studied. According to a plot between 1/Zn (i.e. inverse concentration) and δ⁶⁶Zn value, all the polluted paddy soils fall on the mixing line between acid mine drainage precipitate (AMD-precipitate) and fertilizer while the unpolluted paddy soil falls on the mixing line between fertilizer and bedrock. This indicates the mixing of Zn sources at least three end-members: the mining end-member (i.e. AMD-precipitate), the agricultural end-member (i.e. fertilizer), and bedrock whose geochemical signature is often overprinted by the former two sources around the mining area. The quantitative calculations to apportion the end-member's contributions show that the mining activity contributes most Zn in the paddy soils with an average of ∼66.2%. The contribution of mining activities has significant spatial variations. Specifically, the mining activities have relatively low impacts on the lower reach and the deep soil. Additionally, the apparent Zn isotope fractionation between AMD and AMD-precipitate (Δ⁶⁶Zn_{AMD-precipitate} - _AMD of -0.35 to -0.08‰) in the tailings dam suggests that Zn cations in AMD coprecipitated with the secondary Fe-bearing minerals (e.g. jarosite and goethite). After being discharged from the tailings dam, Zn is mainly carried by the Fe-oxide minerals and migrated during surface runoff. Our study highlights the contribution of human activities to the Zn pollution in the paddy soils and the key role of Fe-bearing minerals in the migration of Zn. These findings provide a scientific base for the development of policy for pollution control in mining-affected region.

Particulate Mercury and Particulate Organic Matter in the Itenez Basin (Bolivia)

In rivers and other freshwater bodies, the presence of mercury can be due to direct contamination by anthropic activities such as gold mining. However, it can also be attributed to atmospheric deposition and erosion, runoff, or lixiviation from surrounding soils. In the case of the Amazon rainforest, high mercury contents have been reported for litter and topsoil, which could affect the mercury concentrations in water bodies. Samples of suspended particulate matter were obtained from a transect of the Itenez River, associated lakes, and some of its tributaries. The aim was to obtain information on particulate mercury’s origin in the study area and determine the relationship between particulate mercury and particulate organic carbon. The concentration of mercury, organic matter, and the C:N ratio of the suspended matter was determined. The concentration of particulate mercury by water volume depended on changes in suspended matter loads, which in turn were mostly affected by the nature of the watershed or sediment resuspension. The observed values for the percentage of organic matter and the C:N ratio suggest that most of the mercury content in rivers and lakes originated from soils. A positive correlation was found between mercury concentration by weight of particulate matter and organic carbon content in particles. This correlation might be due to the direct binding of mercury to organic matter through functional groups like thiols or to an indirect effect of oxyhydroxides that can adsorb mercury and are associated with organic matter.

Recent advances in understanding and measurement of Hg in the environment: Surface-atmosphere exchange of gaseous elemental mercury (Hg0)

The atmosphere is the major transport pathway for distribution of mercury (Hg) globally. Gaseous elemental mercury (GEM, hereafter Hg⁰) is the predominant form in both anthropogenic and natural emissions. Evaluation of the efficacy of reductions in emissions set by the UN's Minamata Convention (UN-MC) is critically dependent on the knowledge of the dynamics of the global Hg cycle. Of these dynamics including e.g. red-ox reactions, methylation-demethylation and dry-wet deposition, poorly constrained atmosphere-surface Hg⁰ fluxes especially limit predictability of the timescales of its global biogeochemical cycle. This review focuses on Hg⁰ flux field observational studies, namely the theory, applications, strengths, and limitations of the various experimental methodologies applied to gauge the exchange flux and decipher active sub-processes. We present an in-depth review, a comprehensive literature synthesis, and methodological and instrumentation advances for terrestrial and marine Hg⁰ flux studies in recent years. In particular, we outline the theory of a wide range of measurement techniques and detail the operational protocols. Today, the most frequently used measurement techniques to determine the net Hg⁰ flux (>95% of the published flux data) are dynamic flux chambers for small-scale and micrometeorological approaches for large-scale measurements. Furthermore, top-down approaches based on Hg⁰ concentration measurements have been applied as tools to better constrain Hg emissions as an independent way to e.g. challenge emission inventories. This review is an up-dated, thoroughly revised edition of Sommar et al. 2013 (DOI: 10.1080/10643389.2012.671733). To the tabulation of >100 cited flux studies 1988-2009 given in the former publication, we have here listed corresponding studies published during the last decade with a few exceptions (2008-2019). During that decade, Hg stable isotope ratios of samples involved in atmosphere-terrestrial interaction is at hand and provide in combination with concentration and/or flux measurements novel constraints to quantitatively and qualitatively assess the bi-directional Hg⁰ flux. Recent efforts in the development of relaxed eddy accumulation and eddy covariance Hg⁰ flux methods bear the potential to facilitate long-term, ecosystem-scale flux measurements to reduce the prevailing large uncertainties in Hg⁰ flux estimates. Standardization of methods for Hg⁰ flux measurements is crucial to investigate how land-use change and how climate warming impact ecosystem-specific Hg⁰ sink-source characteristics and to validate frequently applied model parameterizations describing the regional and global scale Hg cycle.

Preparation, characterization and application of activated carbon from corn cob by KOH activation for removal of Hg(II) from aqueous solution

In the present study, activated carbon was prepared from corn cob. Corn cob by potassium hydroxide activation. SEM, BET, Raman, FTIR and XPS analysis methods were used to characterize the physical and chemical properties of activated carbon. The effects of adsorbent dosage, adsorption time, pH and initial Hg(II) concentration on mercury ion removal rate were studied. The specific surface area of this material is 1054.2 m2 g-1. The Langmuir and Freundlich adsorption models were used to verify the adsorption isotherms. The adsorption isotherms were simulated well by the Langmuir model, which implied that it is a monolayer adsorption process. The kinetic data conformed to the pseudo-second-order model, which implied that the predominant process is chemisorption.

Population-based dietary exposure to mercury through fish consumption in the Southern Peruvian Amazon

BACKGROUND

Mercury exposure related to artisanal and small-scale gold mining (ASGM) has raised environmental and public health concerns globally. Exposure to mercury, a potent neurotoxin that bioaccumulates in fish, is especially of concern to women of childbearing age (WCBA) and children in high-fish consuming populations. In Madre de Dios (MDD), Peru, an Amazon region with naturally occurring mercury and high ASGM activity, there is significant exposure concern among the mainly riverine, fish-consuming communities. The objective of this study was to conduct the first assessment of mercury exposure in a population-based sample of MDD, identify factors associated with elevated levels and compare the relationship between fish consumption and hair total mercury (H-THg) among persons living in ASGM affected and non-ASGM affected watersheds.

METHODS

Hair samples and household demographic surveys, including a module on fish consumption, were collected from 723 participants across 46 communities within 10 km of the Interoceanic Highway in MDD, who were previously enrolled in the first population-based study in MDD spanning areas affected and unaffected by ASGM. H-THg concentration (natural log transformed) was evaluated for association with independent demographic variables through multilevel multivariate regression models accounting for clustering among households and communities. Samples from canned fish available at local stores were also tested for total mercury.

RESULTS

Fish consumption (diversity and total consumed) varied spatially along the highway. 269 participants (37.2%) had elevated H-THg (>2.2 μg/g; median 1.60 μg/g; mean 2.24 μg/g), including 42.7% of WCBA and 20.0% of children under 5. Overall, H-THg was higher among people living in ASGM-affected areas. H-THg concentrations were strongly associated with fish consumption; however, in the multivariate models, household consumption of high trophic level fish was associated with elevated H-THg only in communities located in the ASGM-impacted watersheds. Similarly, the relationship between living in a household engaged in economic activities of fishing or Brazil nut harvesting was associated with higher H-THg, but only among households in the ASGM-affected area. In the non-ASGM affected areas, we observed a positive relationship between household daily fruit consumption and H-THg that was not observed in ASGM-affected areas.

CONCLUSION

Diet, residential location, and occupation are strong predictors of mercury exposure in Madre de Dios, Peru. Canned fish may represent a previously overlooked source of dietary Hg exposure in the region. In accordance with the Minamata Convention on Mercury, the significant environmental health concern of mercury exposure in ASGM areas demands policy and programmatic attention.

Seasonal Fluctuation of Polycyclic Aromatic Hydrocarbons and Aerosol Genotoxicity in Long-Range Transported Air Mass Observed at the Western End of Japan

In order to clarify the level transboundary air pollution caused by polycyclic aromatic hydrocarbons (PAHs) and genotoxic substances, aerosols were collected from forest and suburban sites in Nagasaki, west Japan, for 6 years. The PAH concentration was measured, and the genotoxicity of the substances were evaluated using the umu test. The results showed no notable trends in the concentration or toxicity of either sites throughout the study period. The suburban and forest sites shared similar seasonal fluctuation patterns and quantitative values, suggesting that the western end of Japan might be affected by long-range transported pollutants, especially in winter. PAH concentration and genotoxicity showed the same seasonal patterns of increased levels in winter and lower levels in summer. This suggests that PAHs and genotoxic substances were correlated and share common sources. Back trajectory and source analyses were conducted using the diagnostic ratios of PAHs. It was predicted that air pollution by PAHs at the forest site arise predominantly as a result of biomass or coal combustion in continental regions, such as northern parts of China and the Korean Peninsula. This is particularly expected in winter. Therefore, genotoxic substances would also be strongly influenced by transboundary pollution from the continental region. In addition, it was estimated that the contribution of transboundary PAH pollution could reach 70% at the suburban site in winter.

Mercury accumulation in freshwater and marine fish from the wild and from aquaculture ponds

We analysed the total mercury (Hg) accumulation in bodies and gut contents of 13 species of marine wild fish, 7 species of wild freshwater fish and 4 species of farmed fish. In addition, metal concentrations were recorded in water, sediment, fish prey and fodder materials, to track the dynamics of bio-accumulation. Cultured freshwater fish were collected at four Austrian farms and compared with samples obtained from markets. Wild marine fish were collected at Santa Croce bank, in Italy (Mediterranean Sea). Metal accumulation varied with sampling site, species, and age (or weight) of fish. Wild marine fish exhibited higher levels than wild freshwater fish, which in turn had higher Hg levels than cultured freshwater fish. Mercury increased according to trophic levels of consumers. Total Hg contents in muscle of cultured and wild freshwater fish sampled in 2006-2008 did not exceed legal nutritional limits. Similarly, in market samples of trout and carp collected in 2019, we found low or undetectable concentrations of total Hg in muscle tissue. In contrast, some marine fish (both market samples and some species from coastal waters) exceeded the legal limits. Environmental contamination, food webs and biological factors are the main causes of Hg accumulation in fish. Our results reflect the actual differences between specific European sites and should not be generalized. However, they support the generally increasing demand for monitoring mercury pollution in view of its impact on human health and its value as an indicator of ecosystem contamination.

Mercury isotopic signatures of tailings from artisanal and small-scale gold mining (ASGM) in southwestern Ecuador

Artisanal and small-scale gold mining (ASGM) is currently one of the largest anthropogenic sources of mercury (Hg) to the atmosphere and a significant source to downstream terrestrial aquatic systems. Given the potential toxicity of Hg when it is released to aquatic ecosystems, both scientific and regulatory communities have interest in the development of tools and methods for understanding the fate and transport of Hg in the environment. Although Hg isotopes are applied extensively to trace other anthropogenic point sources of Hg in aquatic ecosystems, few studies have used isotopic analyses to investigate the downstream impacts of ASGM. Furthermore, these studies are currently limited by relatively sparse Hg isotopic analyses on ASGM materials. In this study, ASGM samples from Portovelo-Zaruma (Ecuador), representing various stages of the processing of low-grade gold-bearing ores, were analyzed for Hg concentrations and stable isotope ratios. These data were used to assess the isotopic variability of the ASGM endmember and confirm the results of prior isotopic analyses of ASGM materials and downstream sediments from Portovelo-Zaruma. While the Hg concentrations of the ASGM samples varied significantly, isotopic analyses revealed a limited range of signatures that was characterized by relatively heavy mass-dependent fractionation (MDF) with little to no significant mass-independent fractionation (MIF). The signatures of ASGM samples analyzed in this study matched well with previously reported ASGM samples from Portovelo-Zaruma as well as downstream sediments (for up to 120 km). Furthermore, the overall Hg isotopic compositions of potential ASGM endmembers are distinct from typical compositions observed in freshwater ecosystems (e.g., from soil erosion, atmospheric deposition), allowing Hg isotopes to be a powerful tool in tracing downstream Hg contamination from ASGM.

TGF-β1 alleviates HgCl2 induced apoptosis via P38 MAPK signaling pathway in human trophoblast cells

It is well known that embryonic development can be perturbed by environmental factors such as heavy metals. Mercury is one of the most significant threats to the environment and human health. Mercury can damage many parts of the human body, including lungs, kidneys, nerves and fetus. However, the effect of mercury on human embryo remains unknown. Here, we showed that HgCl₂ treatment resulted in a significant increase in apoptosis in HTR-8/SVneo cells. However, the effect of HgCl₂ on apoptosis was partially reduced by the combination treatment with TGF-β1 and HgCl₂ in HTR-8/SVneo cells. Moreover, HgCl₂ treatment gradually decreased the expression of TGF-β1 in a dose dependent manner. Furthermore, a P38 MAPK inhibitor, SB202190, decreased the cell apoptosis and caspase activation induced by HgCl₂ in trophoblast cells. In addition, TGF-β1 alleviated HgCl₂ induced apoptosis of HTR-8/SVneo cells via p38 MAPK signaling pathway, which was involved in the TAK1 expression. These results might provide a theoretical basis for mercury induced trophoblast associated embryo damage and a potential avenue of intervention.

Tracking legacy mercury in the Hackensack River estuary using mercury stable isotopes

Spatial redistribution of legacy mercury (Hg) contamination in the Hackensack River estuary (New Jersey, USA) was evaluated using mercury stable isotopes. Total Hg varied from 0.06 to 3.8 μg g^-1 in sediment from the tidal Hackensack River and from 15 to 154 μg g^-1 near historically contaminated sites in upper Berry's Creek, a tributary of the Hackensack River. δ²⁰²Hg values for total Hg from Berry's Creek and Hackensack River estuaries varied over a fairly narrow range (-0.44‰ to -0.21‰), but were highest for sediment from upper Berry's Creek. Isotope mixing plots show that residual legacy mercury from upper Berry's Creek is partially diluted by a low concentration and low δ²⁰²Hg pool of mercury associated with low organic matter content sediments similar to those in Newark Bay. Based on an isotope mixing model, we estimate that upper Berry's Creek contributes 21%-82% of the mercury in sediments in the Hackensack River estuary and its tidal tributaries, including upstream marsh habitats far from the primary source. Our results show that mercury stable isotopes can be used to track the redistribution of mercury in tidal ecosystems and highlight the potentially large areas which may be affected by legacy mercury contamination in estuaries.

Mercury Isotope Fractionation in the Subsurface of a Hg(II) Chloride-Contaminated Industrial Legacy Site

To understand the transformations of mercury (Hg) species in the subsurface of a HgCl₂-contaminated former industrial site in southwest Germany, Hg isotope analysis was combined with an investigation of Hg forms by a four-step sequential extraction protocol (SEP) and pyrolytic thermodesorption. Data from two soil cores revealed that the initial HgCl₂ was partly reduced to metallic Hg(0) and that Hg forms of different mobility and oxidation state coexist in the subsurface. The most contaminated sample (K2-8, 802 mg kg^-1 Hg) had a bulk δ²⁰²Hg value of around -0.43 ± 0.06‰ (2SD), similar to published average values for industrial Hg sources. Other sample signatures varied significantly with depth and between SEP pools. The most Hg-rich samples contained mixtures of Hg(0) and Hg(II) phases, and the water-extractable, mobile Hg pool exhibited heavy δ²⁰²Hg values of up to +0.18‰. Sequential water extracts revealed slow dissolution kinetics of mobile Hg pools, continuously releasing isotopically heavy Hg into solution. This was further corroborated by heavy δ²⁰²Hg values of groundwater samples. Our results demonstrate that the Hg isotope signature of an industrial contamination source can be significantly altered during the transformations of Hg species in the subsurface, which complicates source tracing applications but offers the possibility of using Hg isotopes as process tracers in contaminated subsurface systems.

Quantifying the impacts of artisanal gold mining on a tropical river system using mercury isotopes

In some locations, artisanal and small-scale gold-mining (ASGM) represents a significant source of anthropogenic Hg to freshwater environments. The Hg released from ASGM can contaminate aquatic fauna and pose health risks to downstream populations. Total Hg (THg) concentrations, speciation, and isotopic compositions were analyzed in water, suspended particulate matter, soil, and bottom sediment samples from pristine areas and in places of active and legacy gold mining along the Oyapock River (French Guiana) and its tributaries. Mass-independent fractionation (MIF) of even Hg isotopes in top soils (Δ²⁰⁰Hg = -0.06 ± 0.02‰, n = 10) implied the uptake of gaseous Hg(0) by plants, rather than wet deposition, as the primary Hg source. Odd isotope MIF was lower in deep soils (Δ¹⁹⁹Hg = -0.75 ± 0.03‰, n = 7) than in top soils (Δ¹⁹⁹Hg = -0.55 ± 0.15‰, n = 3). This variation could be attributed to differences between the isotopic signatures of modern and pre-industrial atmospheric Hg. Combining a Hg-isotope binary mixing model with a multiple linear regression based on physico-chemical parameters measured in the sediment samples, we determined that active mined creek sediments are contaminated by ASGM activities, with up to 78% of THg being anthropogenic. Of this anthropogenic Hg, more than half (66-74%) originates from liquid Hg(0) that is released during ASGM. The remaining anthropogenic Hg comes from the ASGM-driven erosion of Hg-rich soils into the river. The isotope signatures of anthropogenic Hg in bottom sediments were no longer traceable in formerly mined rivers and creeks.

Distribution, sources and consequences of nutrients, persistent organic pollutants, metals and microplastics in South American estuaries

Estuarine pollution imposes rapid, increasing and lasting environmental modifications. In the present review, especial attention is given to estuaries in South America (SA), where legislation, policies and actions to guarantee environmental quality remain ineffective. There, the majority of estuaries face uncontrolled occupation of its margins by urban and industrial centres, agriculture and aquaculture expansion, water extraction and flow control. The lack of basic sanitation and poor environmental management (including territories within Marine Protected Areas) often lead to hydrological alterations, high nutrient loads, and the presence and dynamics of pollutants (nutrient loads, persistent organic pollutants (POPs), metals and plastic debris) along the entire estuarine ecocline. Organic enrichment has increased dissolved oxygen consumption, with wide spatio-temporal variability along latitudes and estuarine gradients. The toxicity, biogeochemistry and availability of metals and POPs depend on the annual fluctuations of salinity, water renewal, dissolved oxygen levels, suspended particulate loads, sediment mobility, grain size and composition at the sink. Plastic debris from land sources are widespread in estuaries, where they continue to fragment into microplastics. River basins are the main contributors of plastics to estuaries, whose transportation and accumulation are subjected to interannual water flow variations. Although some systems seems to be in a better condition in relation to others around the world (e.g. Goiana and Negro estuaries), many others are among the most modified worldwide (e.g. Guanabara Bay and Estero Salado System). We propose that, estuarine conservation plans should consider year-round fluctuations of the ecocline and the resulting cycles of retention and flush of environmental signals and their influence on trophic webs over the whole extent of estuarine gradients.