Source Of Hg Research Articles

Environmental forensics approach to source investigation in a mercury contaminated river: Insights from mercury stable isotopes

Environmental forensics approach was applied to assess the efficacy of mercury (Hg) stable isotopes for source screening and decision-making in the Hyeongsan River, South Korea. Four Hg contamination scenarios were identified− atmospheric Hg emissions from a steel manufacturing industry, upstream riverine Hg transport, and industrial Hg releases and historical landfill collapse from Gumu Creek. The absence of significant Hg isotope difference between the Hyeongsan River sediments (δ202Hg; −0.46 ± 0.17‰, Δ199Hg; −0.04 ± 0.06‰) and the Gumu Creek sediment (δ202Hg; −0.39 ± 0.26‰, Δ199Hg; −0.04 ± 0.03‰) confirm that Hg source is originated from Gumu Creek. The heterogeneous Hg distribution throughout Gumu Creek and statistically similar Hg isotope ratios between Gumu Creek and solid waste cores from the landfill suggests that the landfill collapse is the dominant source to the Hyeongsan-Gumu system. Present Hg releases is also possible given the elevated and matching Δ199Hg between some riverine sediments and wastewater sampled from the landfill. The ternary mixing model estimates that the landfill collapse and wastewater releases contribute 61 ± 25 % and 22 ± 11 %, and the regional background, reflecting terrestrial runoff using deep sediment cores, explain 17 ± 24 % of Hg to the riverine sediment. We suggest that Hg isotopes can be used for routine source screening in areas where Hg sources are unknown.

Mercury Isotope Values in Shoreline Spiders Reveal the Transfer of Aquatic Mercury Sources to Terrestrial Food Webs.

The transfer of aquatic contaminants, including mercury (Hg), to terrestrial food webs is an often-overlooked exposure pathway to terrestrial animals. While research has implemented the use of shoreline spiders to assess aquatic to terrestrial Hg transfer, it is unclear whether Hg sources, estimated from isotope ratios, can be successfully resolved to inform site assessments and remedy effectiveness. To examine aquatic to terrestrial Hg transfer, we collected shoreline spiders (Tetragnatha spp.) and aquatic insect larvae (suborder Anisoptera) across a mosaic of aquatic and shoreline habitats in the St. Louis River and Bad River, tributaries to Lake Superior. The fraction of industrial Hg in sediments was reflected in the δ202Hg values of aquatic dragonfly larvae and predatory fish, connecting benthic Hg sources to the aquatic food web. Shoreline spiders mirrored these aquatic Hg source signatures with highly positive correlations in δ202Hg between tetragnathids and dragonfly larvae (r2 = 0.90). Further assessment of different spider taxa (i.e., araneids and pisaurids) revealed that differences in prey consumption and foraging strategies resulted in isotope differences, highlighting the importance of spider taxa selection for Hg monitoring efforts.

Mercury Sources and Fate in a Large Brackish Ecosystem (the Baltic Sea) Depicted by Stable Isotopes.

Identifying Hg sources to aquatic ecosystems and processes controlling the levels of monomethylmercury (MMHg) is critical for developing efficient policies of Hg emissions reduction. Here we measured Hg concentrations and stable isotopes in sediment, seston, and fishes from the various basins of the Baltic Sea, a large brackish ecosystem presenting extensive gradients in salinity, redox conditions, dissolved organic matter (DOM) composition, and biological activities. We found that Hg mass dependent fractionation (Hg-MDF) values in sediments mostly reflect a mixing between light terrestrial Hg and heavier industrial sources, whereas odd Hg isotope mass independent fractionation (odd Hg-MIF) reveals atmospheric inputs. Seston presents intermediate Hg-MDF and odd Hg-MIF values falling between sediments and fish, but in northern basins, high even Hg-MIF values suggest the preferential accumulation of wet-deposited Hg. Odd Hg-MIF values in fish indicate an overall low extent of MMHg photodegradation due to limited sunlight exposure and penetration but also reveal large spatial differences. The photodegradation extent is lowest in the central basin with recurrent algal blooms due to their shading effect and is highest in the northern, least saline basin with high concentrations of terrestrial DOM. As increased loads of terrestrial DOM are expected in many coastal areas due to global changes, its impact on MMHg photodegradation needs to be better understood and accounted for when predicting future MMHg concentrations in aquatic ecosystems.

Pollution Characteristics and Sources of Heavy Metals in Soil of a Typical Pyrite Concentrated Mining Area in Anhui Province

To identify the characteristics and sources of heavy metal pollution in the surrounding soil of a typical pyrite concentrated mining area in Anhui Province, the pH value and the concentrations of Zn, Cu, Cd, Pb, Cr, Ni, Hg, and As in 42 surface soil samples and 16 soil samples from two vertical sections in the study area were collected and measured. The distribution characteristics, pollution assessment, and source analysis of heavy metal elements were conducted using the ArcGis inverse distance weight interpolation method, Nemero comprehensive index method, principal component analysis method, and absolute factor score-multiple linear regression (APCS-MLR) receptor model. The results showed that the average concentration of the eight heavy metals was 1.03-13.14 times the background value in the Tongling area. The local enrichment of Zn, Cu, Cd, Pb, Hg, and As was obvious, and the spatial distribution was basically consistent with the location of man-made mining activities. The single-factor pollution index evaluation showed that Zn, Cu, Cd, Pb, and As had different degrees of pollution risk, and the pollution degree of Cd and Cu was the most serious, accounting for 47.62% and 42.86% of moderate pollution, respectively. The Nemerow comprehensive pollution index evaluation showed that 61.90% of the soil samples in the study area were moderately polluted. The ground accumulation index evaluation showed that the pollution degree of Zn, Cu, Cd, Pb, Hg, and As in the study area was mainly from light pollution to strong pollution. In the vertical soil profile variation, heavy metals were easily enriched in the surface layer of the soil but migrated slowly to the deep layer, with concentrations mainly above 1 m. The results of source analysis showed that the high geological background and mining contribution rates of Zn, Pb, and As were 37.82%, 43.49%, and 46.63%, respectively. The natural contribution rates of weathering of parent material were 34.02%, 40.88%, and 38.52%, respectively. The sources of Cr and Ni were mainly natural sources of weathering of the parent material, with contribution rates of 91.95% and 73.68%, respectively. Geological high background and mining activities contributed 41.91% of the Cu sources, and atmospheric sedimentation and agricultural comprehensive sources contributed 41.30%. There were many sources of Hg. The natural source of weathering of soil parent material contributed 35.60%, geological high background and mining activities contributed 29.87%, and unknown sources contributed 34.05%. The main source of Cd was atmospheric sedimentation and agricultural comprehensive sources, contributing 81.81%.

Mercury budgets in the suspended particulate matters of the Yangtze River.

Riverine processes are crucial for the biogeochemical cycle of mercury (Hg). The Yangtze River, the largest river in East Asia, discharges a substantial amount of Hg into the East China Sea. However, the influencing factors of the Hg budget and its recent trends remain unclear. This study quantitatively analyzed the total Hg concentration (THg) in suspended particulate matter (SPM) in the Yangtze River and calculated the Hg budget in 2018 and 2021. The results showed that the total Hg concentrations varied substantially along the river, with concentrations ranging from 23 to 883μg/kg in 2018 and 47 to 146μg/kg in 2021. The average Hg flux to China Sea in 2018 and 2021 were approximately 10 Mg/yr, lower than in 2016 (48 Mg/yr). Over 70% of the SPM was trapped in the Three Gorges Dam (TGD), and 22 Mg/yr of Hg settled in the TGD in 2018 and 10 Mg/yr in 2021. Hg fluxes in the Yangtze River watershed were driven by various factors, including decreased industrial emissions, increased agriculture emissions, and decreased soil erosion flux. We found that in the upper reach of the Yangtze River changed from sink to source of Hg possibly due to the resuspension of sediments, which implies that the settled sediments could be a potential source of Hg for downstream. Overall, emission control policies may have had a positive impact on reducing Hg flux to the East China Sea from 2016 to 2021, but more efforts are needed to further reduce Hg emissions.

The consumption of ice-derived resources is associated with higher mercury contamination in an Arctic seabird

Sea ice plays a fundamental role in Arctic marine environments, by driving primary productivity and sustaining ice-associated ecosystems. Simultaneously, sea ice influences the contamination of Arctic marine organisms, by modifying contaminant cycles or their bioavailability. Changes in sea ice conditions could therefore profoundly impact the functioning of Arctic marine food webs and their contamination. Top predators such as seabirds, which are subject to bioaccumulation and biomagnification of contaminants, are particularly exposed. In this context, the present study aims to investigate the influence of sea ice and of the use of ice-derived resources on the contamination of seabirds by mercury (Hg). To this end, eggs of thick-billed murres (Brünnich's guillemots, Uria lomvia; n = 60) were collected on Prince Leopold Island (Canadian High Arctic) during four years of varying ice conditions (2010–2013). Trophic tracers (i.e., Highly Branched Isoprenoids, HBIs – an indicator of the use of ice-derived resources; carbon and nitrogen stable isotopes – indicators of foraging habitats and trophic status), as well as total Hg concentrations were quantified. Results showed that feeding on ice-derived resources (as indicated by HBI concentrations) was positively correlated to sea ice cover, and both positively influenced Hg concentrations in murre eggs. However, when testing for the best predictor with model selection, sea ice concentration only drove Hg contamination in murres. This work provides new insights into the role of sea ice and ice-derived resources in the contamination by Hg of Arctic wildlife. Further research is now needed to better understand the relationship between sea ice and Hg contamination in Arctic biota and its underlying mechanisms, but also to identify Hg sources in rapidly changing environmental conditions in the Arctic.

Contrasting mercury contamination scenarios and site susceptibilities confound fish mercury burdens in Suriname, South America

In Suriname, mercury (Hg) use has recently increased because of gold mining, which has put fish-reliant communities (e.g., Indigenous and Tribal) at risk of enhanced Hg exposure through the riverine fish these communities consume. To quantify how the magnitude of these risks change according to location and time, we measured total mercury (HgT) in fish at sites downstream and upstream of an artisanal and small-scale gold mining (ASGM) operation in 2004–2005 and in 2017–2018. We tested whether fish HgT burdens over dynamic ranges were increased. Surprisingly, our findings did not support broadly increased fish Hg burden over time or that proximity to ASGM was diagnostic to fish HgT-burden. Subsequently, we elected to test the HgT stable isotope ratios on a set of freshly collected 2020 fish to determine whether differences in Hg source and delivery pathways might cofound results. We found that remote unmined sites were more susceptible to gaseous elemental Hg deposition pathways, leading to enhanced risk of contamination, whereas ASGM proximate sites were not. These results highlight that elemental mercury releases from ASGM practices may have significant impact on fish-reliant communities that are far removed from ASGM point source contamination.

The Marginal Ice Zone as a dominant source region of atmospheric mercury during central Arctic summertime

Atmospheric gaseous elemental mercury (GEM) concentrations in the Arctic exhibit a clear summertime maximum, while the origin of this peak is still a matter of debate in the community. Based on summertime observations during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition and a modeling approach, we further investigate the sources of atmospheric Hg in the central Arctic. Simulations with a generalized additive model (GAM) show that long-range transport of anthropogenic and terrestrial Hg from lower latitudes is a minor contribution (~2%), and more than 50% of the explained GEM variability is caused by oceanic evasion. A potential source contribution function (PSCF) analysis further shows that oceanic evasion is not significant throughout the ice-covered central Arctic Ocean but mainly occurs in the Marginal Ice Zone (MIZ) due to the specific environmental conditions in that region. Our results suggest that this regional process could be the leading contributor to the observed summertime GEM maximum. In the context of rapid Arctic warming and the observed increase in width of the MIZ, oceanic Hg evasion may become more significant and strengthen the role of the central Arctic Ocean as a summertime source of atmospheric Hg.

Quantifying the impacts of coal mining activities on topsoil using Hg stable isotope: A case study of Guqiao mining area, Huainan City

The Hg released from coal mining activities can endanger soil ecosystems and pose a risk to human health. Understanding the accumulation characteristics of mercury (Hg) in coal mining soil is important for effectively controlling Hg emissions and developing measures for the prevention and control of Hg contamination. To identify the potential sources of Hg in soils, the Hg concentration and isotopic composition characteristics of raw coal and different topsoil types from the areas surrounding a coal mine were determined in this study. The results showed that Hg in coal mainly exists mainly in the form of inorganic Hg, and Hg has experienced Hg2+ photoreduction prior to incorporating into coal. In addition, the composition of Hg isotopes differed significantly among different topsoil types, and the δ202Hg value of the farmland soil exhibited large negative excursions compared to the coal mining soil. The ternary mixed model further revealed the presence of substantial differences in potential Hg sources among the two regions, with the coal mining soil being greatly disturbed by anthropogenic activity, and the relative contributions of Hg from raw coal, coal gangue, and background soil to coal mining soil being 33.42%, 34.4%, and 32.19%, respectively. However, Hg from raw coal, coal gangue and background soil contributed 17.04%, 21.46%, and 61.51% of the Hg in the farmland soil, indicating that the accumulation of Hg in farmland soil was derived primarily from the background soil. Our study demonstrated that secondary pollution in soil caused by immense accumulation of solid waste (gangue) by mining activities offers a significant challenge to ecological security. These findings provide new insights into controlling soil Hg in mining areas and further highlight the urgency of strict protective measures for contaminated sites.

The mercury flow through a terrestrial songbird food chain in subtropical pine forest: Elucidated by Bayesian isotope mixing model and stable mercury isotopes

In order to comprehend the transfer of inorganic mercury (IHg) and methylmercury (MeHg) within food chains in terrestrial pine forests, we collected samples of Great Tit nestlings, common invertebrates, plants, and soil in a subtropical pine forest and used Bayesian isotope mixing model analysis, Hg daily intake, and stable Hg isotopes to elucidate the flow of MeHg and IHg in these food chains. Results indicate that caterpillars and cockroaches are the predominant prey items for nestlings, accounting for a combined contribution of 81.5%. Furthermore, caterpillars, cockroaches, and spiders were found to contribute the most (∼80%) of both IHg and MeHg that dietary accumulated in nestlings. The provisoned invertebrates tend to supply more IHg and diluting the proportion of MeHg as total Hg (MeHg%). Notably, nestling feathers displayed the highest Δ199Hg values but a relatively lower MeHg%, suggesting an imbalanced incorporation of Hg from maternal transfer and dietary accumulation during the nestling stage. This study highlights the efficacy of nestlings as indicators for identifying Hg sources and transfers in avian species and food chains. However, caution must be exercised when using Hg isotope compositions in growing feathers, and the contribution of maternally transferred Hg should not be ignored.

Non-conservative mixing behaviors of mercury in subterranean estuary: Coupling effect of hydrological and biogeochemical processes and implications for rapidly changing world

Coastal ecosystem is an important zone of mercury (Hg) storage and hotspot of neurotoxic methylmercury (MMHg) production and bioaccumulation. The releases of Hg from coastal aquifer or subterranean estuary (STE) via submarine groundwater discharge (SGD) to coastal waters provide an important source of Hg from land to seas. However, the transport and biogeochemical transformation of Hg in STEs are less quantified. In this study, we documented total Hg (THg) and MMHg dynamics in two distinct STEs (a sandflat at an open coast versus a mudflat at a bay) during two different seasons (December versus August) in the temperate coast of northern China, and further applied the salinity‐based conservative mixing model (CMM) to quantify the coupling effect of hydrological and biogeochemical processes on STE Hg cycle. Our field data presented large variations of THg and MMHg concentrations and%MMHg/THg of groundwater and sediment in both STEs over time and space. The CMM results clearly displayed substantial divergences of dissolved THg and MMHg from salinity in groundwater between sites and seasons, and the concentration and percent deviations in the Hg-rich mudflat were significantly higher than those in the Hg-poor sandflat. Our findings indicate the non-conservative mixing behaviors of Hg along the groundwater flow paths of both STEs, and the Hg-rich intertidal zone could be hotspot for the production and source of dissolved THg and MMHg to coastal waters via SGD. Our results provide field evidence to highlight that the hydrological shifts and biogeochemical processes collectively drive complex transport and biogeochemical transformation of Hg in STEs. The non-conservative mixing behaviors of Hg in STEs also highlight that, for more accurately calculating SGD-derived Hg fluxes to coastal seas, we need to carefully select the groundwater zonation of STE to better represent the output endmember. Our findings also address that human activities and climate change will profoundly alter the Hg biogeochemical cycle and toxicology in global coastal aquifers.

Mercury occurrence and speciation in sediments from hard coal mining in Czechia

This study examines Hg distribution in stream sediments impacted by hard coal mining in the Upper Silesian Coal Basin (USCB), Czechia. By means of a comparative analysis, geological samples and samples from stream sediments were used to carry out a comprehensive assessment of the effects of anthropogenic activities on Hg distribution and speciation. Total Hg (THg), total organic and inorganic carbons (TOC and TIC), and total sulphur (TS) were measured in the samples to reveal a potential relationship. In addition, THg and TS species were discussed in order to elucidate their mobility pattern in the environment. The results have shown that there are no correlations between THg, TS, and TOC indicating overlapping Hg sources attributed to industrial processes. Geological samples, particularly coal and associated sedimentary rocks, contained lower Hg concentrations compared to a variety of stream sediments. The main Hg species identified in the samples was a stable β-HgS, which decreases its mobility in the riverine environment. It follows that Hg enrichment and speciation is linked to industrial processes, which are the main origin/cause for Hg enrichment and transformation. Minor proportions of HgO in some samples show Hg oxidation upon diagenesis, while HgCl2 is attributed to the chemical loads from the former coking plant.

Mercury isotope compositions in seawater and marine fish revealed the sources and processes of mercury in the food web within differing marine compartments.

Anthropogenic activities and climate change have significantly increased mercury (Hg) levels in seawater. However, the processes and sources of Hg in differing marine compartments (e.g. estuary, marine continental shelf (MCS) or pelagic area) have not been well studied, which makes it difficult to understand Hg cycling in marine ecosystems. To address this issue, the total Hg (THg) concentration, methylmercury (MeHg) concentration and stable Hg isotopes were determined in seawater and fish samples collected from differing marine compartments of the South China Sea (SCS). The results showed that the estuarine seawater exhibited substantially higher THg and MeHg concentrations than those in the MCS and pelagic seawater. Significantly negative δ202Hg (-1.63‰ ± 0.42‰) in estuarine seawater compared with that in pelagic seawater (-0.58‰ ± 0.08‰) may suggest watershed input and domestic sewage discharge of Hg in the estuarine compartment. The Δ199Hg value in estuarine fish (0.39‰ ± 0.35‰) was obviously lower than that in MCS (1.10‰ ± 0.54‰) and pelagic fish (1.15‰ ± 0.46‰), which showed that relatively little MeHg photodegradation occurred in the estuarine compartment. The Hg isotope binary mixing model based on Δ200Hg revealed that approximately 74% MeHg in pelagic fish is derived from atmospheric Hg(II) deposition, and over 60% MeHg in MCS fish is derived from sediments. MeHg sources for estuarine fish may be highly complex (e.g. sediment or riverine/atmospheric input) and further investigations are warranted to clarify the contribution of each source. Our study showed that Hg stable isotopes in seawater and marine fish can be used to identify the processes and sources of Hg in different marine compartments. This finding is of great relevance to the development of marine Hg food web models and the management of Hg in fish.

Multidimensional Drivers of Mercury Distribution in Global Surface Soils: Insights from a Global Standardized Field Survey.

Soil stores a large amount of mercury (Hg) that has adverse effects on human health and ecosystem safety. Significant uncertainties still exist in revealing environmental drivers of soil Hg accumulation and predicting global Hg distribution owing to the lack of field data from global standardized analyses. Here, we conducted a global standardized field survey and explored a holistic understanding of the multidimensional environmental drivers of Hg accumulation in global surface soils. Hg content in surface soils from our survey ranges from 3.8 to 618.2 μg kg-1 with an average of 74.0 μg kg-1 across the globe. Atmospheric Hg deposition, particularly vegetation-induced elemental Hg0 deposition, is the major source of surface soil Hg. Soil organic carbon serves as the major substrate for sequestering Hg in surface soils and is significantly influenced by agricultural management, litterfall, and elevation. For human activities, changing land-use could be a more important contributor than direct anthropogenic emissions. Our prediction of a new global Hg distribution highlights the hot spots (high Hg content) in East Asia, the Northern Hemispheric temperate/boreal regions, and tropical areas, while the cold spots (low Hg content) are in arid regions. The holistic understanding of multidimensional environmental drivers helps to predict the Hg distribution in global surface soils under a changing global environment.

Tracking the multiple Hg sources in sediments in a typical river-lake basin by isotope compositions and mixing models

In this study, total mercury (THg) contents and Hg isotope compositions in sediments were investigated in the Lianxi River, Zijiang River and South Dongting Lake to identify and quantify multiple Hg sources and evaluate the Hg environmental processes. The THg contents, δ202Hg and Δ199Hg values in sediments were 48.22 ∼ 4284.32 µg/kg, − 1.33 ∼ 0.04‰ and − 0.25 ∼ 0.03‰, respectively. Relatively distinct Hg isotope characteristics of sediments were presented in the Lianxi River, Zijiang River and South Dongting Lake, indicating the dominant Hg sources considerably varied in these regions. Source apportionment based on MixSIAR proved that Hg in sediments mainly originated from industrial activities, and the ternary mixing model concluded non-ferrous metal smelting was the dominant industrial Hg contributor in the Lianxi River. Compared with the Lianxi River, the relative contribution of Hg in sediments from industrial activities significantly decreased, while the relative contributions of Hg from background releases significantly increased in the Zijiang River and South Dongting Lake. Nonetheless, the contribution of industrial Hg in this study area deserves more attention. These results are conducive to further manage Hg pollution.

Appalachian Basin mercury enrichments during the Late Devonian Kellwasser Events and comparison to global records

The Late Devonian Kellwasser Events are two major biodiversity crises recorded at and just below the Frasnian-Famennian stage boundary for which the ultimate cause or causes of diversity depletion remain unclear. The discovery of anomalous mercury (Hg) enrichments in Upper Kellwasser Event (UKE) strata has led to increased interest in a potential volcanic trigger for one or both events. However, UKE Hg anomalies are found mainly on the continental shelves of the Palaeotethys Ocean, and Hg isotope values from at least one distal basin indicate a non-volcanic Hg source. These findings suggest volcanism during the UKE may have had regional rather than global impacts. In comparison to the UKE, few works have investigated the sedimentary Hg record of the Lower Kellwasser Event (LKE). Here, we contribute new Hg data from the LKE of the Appalachian Basin and compare this to a compilation of global Hg data from both events. The Appalachian Basin contains no sedimentary Hg enrichments consistent with massive volcanism during the LKE, and Hg concentrations are strongly correlated with total organic carbon. We argue that organic matter drawdown exerted a primary control upon Hg concentration in the Appalachian Basin. While basins more proximal to the Palaeotethys Ocean preserve potentially volcanogenic LKE Hg anomalies, the absence of such anomalies here reflects volcanism during the LKE that was at most only regionally significant, as hypothesized for the UKE. Volcanism is therefore an unlikely trigger of the global Kellwasser diversity depletions. Broader sampling of the Kellwasser record will assist in the development of an extinction model that accounts for variations in global Hg concentrations, as the depressed origination rates, prolonged background environmental stress, and variations in intra-basinal expression that characterize both events may indicate that the trigger of diversity loss in this interval is unique among the “Big Five” mass extinctions.

Addressing Uncertainties in Potential Human Dietary Exposure to Mercury in the Watershed of the South River, Virginia, USA.

Much has been published about the harmful effects to humans when they are exposed to mercury (Hg) in environmental media including their diet. Numerous health advisories around the world, including for the South River, Virginia, USA, warn against consumption of Hg-contaminated fish species. Fewer studies have focused on other dietary sources of Hg and how to advise humans potentially exposed by this route. In undertaking a human health risk assessment for the former DuPont facility in Waynesboro, Virginia, USA, and the nearby South River and surrounding watershed, the available published information on Hg exposure through dietary consumption of nonfish items proved unsuitable for extrapolation purposes. In response, an evaluation of potential Hg exposure to residents who might consume livestock, poultry, and wildlife raised or collected in the South River watershed was conducted to inform the risk-assessment process. The newly collected data on Hg in these dietary items filled an important data gap, suggesting that there was little concern about limiting dietary consumption for most items. These results were communicated to the public through print and electronic platforms, in the form of "fact sheets." We describe the studies and actions taken to better explain the potential for human exposures to Hg in nonfish dietary items from a portion of the watershed of the South River. Environ Toxicol Chem 2023;42:2237-2252. © 2023 SETAC.

Typical heavy metals accumulation, transport and allocation in a deglaciated forest chronosequence, Qinghai-Tibet Plateau

Understanding heavy metals (HMs) accumulation and transportation is the foundation to assess the ecological risks caused by the pollution of HMs in terrestrial ecosystems. There are large knowledge gaps regarding impacts of vegetation succession on shaping the HMs accumulation, transportation and allocation in the remote alpine regions. Herein, we comprehensively investigated the distribution and source contribution of mercury (Hg), cadmium (Cd) and chromium (Cr) along with vegetation succession in a deglaciated forest chronosequence of Qinghai-Tibet Plateau. Results showed that Hg and Cd were highly enriched in organic soils, while Cr concentrations and pool sizes decreased significantly with the vegetation succession. Atmospheric Hg deposition contributed to the dominant Hg sources in topsoil (74 − 87%), whereas moraine weathering was the main source of Cr (73 − 76%). Both moraine (18 − 48%) and atmospheric deposition inputs (52 − 82%) affected Cd accumulation in topsoil. Over the last century, the accumulation rate of Hg and Cd showed the distinctly decreasing trends due to the vegetation leading to the elevated atmospheric depositions at the earlier deglacial sites. The negative accumulation rate of Cr along with the vegetation succession reflected the formation of organic soil diluting the geogenic inputs of Cr.

Soil heavy metals in tropical coastal interface of eastern Hainan Island in China: Distribution, sources and ecological risks

Coastal interface is the most active in the global element cycling, linking the terrestrial and ocean ecosystem. However, little attention is paid to the ecological risk of multiple heavy metals (HMs) residues in tropical coastal soil and its relationships with human activities. Here, 199 coastal topsoils were collected from the eastern Hainan Island of China in 2021. Furthermore, the pollution characteristics, spatial distribution, and ecological risk of eight HMs were evaluated. The results showed that the mean contents of eight HMs were in the order of Cr (47.96 mg·kg−1) > Zn (40.93 mg·kg−1) > Pb (21.28 mg·kg−1) > Cu (14.89 mg·kg−1) > Ni (8.67 mg·kg−1) > As (5.64 mg·kg−1) > Cd (0.06 mg·kg−1) > Hg (0.05 mg·kg−1). These HMs contents were larger than the soil background values of Hainan Province, indicating the accumulation risk. Based on the Nemerow integrated pollution index, the sample sites with moderate and severe pollution accounted for 28.5% and 28.0%, respectively. In contrast, the sum of sites with no and slight pollution was only 10%. The ecological risk assessment revealed that 25% and 5% of sites displayed moderate or extreme ecological risks with the mean RI value larger than 90, and As and Cd were the most dangerous HMs. Spatially, the pollution hotspots of Zn, Pb, Cd and Hg were distributed in the middle urban of the study area and the dense road network in the west, while that of Cr, Ni, and Cu were distributed in the woodland in the northeast and southwest. The pollution hotspots of As were distributed in northeast cropland. The PMF model further indicated that the largest contributor to Zn, Pb, and Cd were the combined sources of traffic and agricultural activities, accounting for 55.66%, 56.30%, and 55.36%, respectively. Soil parent materials contributed to the Cr, Ni, and Cu, accounting for 77.1%, 58.4%, and 38.2%, respectively. Coal combustion was the main source of Hg, accounting for 81.3%, while agricultural activities accounted for 80.8% of the As in the soils. Overall, anthropogenic activities (63.60%) were the main source for HMs residues in the studied coastal soils, but the contribution of soil parent materials (36.40%) could not be neglected.

Mercury isotopes trace historical mercury pollution from Pb[sbnd]Zn smelter in China

Lead–zinc (PbZn) smelting is one of the largest anthropogenic emission sources of mercury (Hg) in China and the world. In the last few decades, Hg emission control devices have been employed in PbZn smelters to reduce Hg emissions. To evaluate the effectiveness of Hg emission control, this study uses Hg isotopes to trace the sources of Hg in soils and reservoir sediments near the Zhuzhou smelter, the largest Zn production facility in China. The results showed that Hg concentrations in reservoir sediments were higher than those in soils at the three study sites, suggesting that reservoir sediments accumulate more Hg than soils do under the same conditions. Hg concentrations and deposition fluxes in reservoir sediments have dramatically decreased since the year 2000, suggesting the effectiveness of Hg emission control in the Zhuzhou smelter. Mercury isotope compositions in soil suggest binary mixing of Hg from the Zhuzhou smelter and the local background, and the contribution of Hg from the Zhuzhou smelter to soils and sediment is mainly a function of location and distance from the source. The model output suggested that approximately 61–75% of Hg in reservoir sediments was sourced from the Zhuzhou smelter. This study demonstrates that legacy Hg will continue to be a source to local ecosystems, even after Hg emission control has been implemented for decades.