Source Of Hg Research Articles

Using mercury stable isotope fractionation to identify the contribution of historical mercury mining sources present in downstream water, sediment and fish.

Ecosystems downstream of mercury (Hg) contaminated sites can be impacted by both localized releases as well as Hg deposited to the watershed from atmospheric transport. Identifying the source of Hg in water, sediment, and fish downstream of contaminated sites is important for determining the effectiveness of source-control remediation actions. This study uses measurements of Hg stable isotopes in soil, sediment, water, and fish to differentiate between Hg from an abandoned Hg mine from non-mine-related sources. The study site is located within the Willamette River watershed (Oregon, United States), which includes free-flowing river segments and a reservoir downstream of the mine. The concentrations of total-Hg (THg) in the reservoir fish were 4-fold higher than those further downstream (>90 km) from the mine site in free-flowing sections of the river. Mercury stable isotope fractionation analysis showed that the mine tailings (δ202Hg: -0.36‰ ± 0.03‰) had a distinctive isotopic composition compared to background soils (δ202Hg: -2.30‰ ± 0.25‰). Similar differences in isotopic composition were observed between stream water that flowed through the tailings (particulate bound δ202Hg: -0.58‰; dissolved: -0.91‰) versus a background stream (particle-bound δ202Hg: -2.36‰; dissolved: -2.09‰). Within the reservoir sediment, the Hg isotopic composition indicated that the proportion of the Hg related to mine-release increased with THg concentrations. However, in the fish samples the opposite trend was observed-the degree of mine-related Hg was lower in fish with the higher THg concentrations. While sediment concentrations clearly show the influence of the mine, the relationship in fish is more complicated due to differences in methylmercury (MeHg) formation and the foraging behavior of different fish species. The fish tissue δ13C and Δ199Hg values indicate that there is a higher influence of mine-sourced Hg in fish feeding in a more sediment-based food web and less so in planktonic and littoral-based food webs. Identifying the relative proportion of Hg from local contaminated site can help inform remediation decisions, especially when the relationship between total Hg concentrations and sources do not show similar covariation between abiotic and biotic media.

Environmental and Health Risk Assessment Due to Potentially Toxic Elements in Soil near Former Antimony Mine in Western Serbia

Background: Anthropogenic activities have clearly affected the environment, with irreversible and destructive consequences. Mining activities have a significant negative impact, primarily on soil, and then on human health. The negative impact of the first mining activities is represented even today in the soils of those localities. Research shows that, for different types of mines, the concentrations of potentially toxic elements (PTEs) are high, especially in antimony, multi-metal and lead–zinc mines, which have adverse effects on the environment and then on human health and the economy. A large flood in 2014 in Western Serbia resulted in the breaking of the dam of the processed antimony ore dump of the former antimony mine, causing toxic tailings to spill and pollute the downstream area. Due to this accident, tailings material flooded the area downstream of the dump, and severely affected the local agriculture and population. Methods: Potentially toxic elements content, pollution indices and health indices were determined in soil samples from the flooded area, using referenced methodologies. The sources and routes of pollutants and risks were determined and quantified using statistical principal component analysis, positive matrix factorisation, and a Monte Carlo simulation. Results: The main source of As, Cd, Hg, Pb, Sb and Zn in the upper part of the study area was the tailing material. Based on the pollution indices, about 72% of the studied samples show a high risk of contamination and are mainly distributed immediately downstream of the tailings dump that was spilled due to heavy rainfall. Conclusions: Although the content of the PTEs is high, there is no non-carcinogenic risk for any PTEs except As, for which a threshold risk was determined. There is no carcinogenic risk in the study area.

Contamination and Risk Assessment of Potentially Toxic Elements in Coastal Sediments of the Area between Al-Jubail and Al-Khafji, Arabian Gulf, Saudi Arabia

Coastal environments need continuous environmental risk assessment, especially with increasing coastal development and human activities. The present work evaluates the distribution, contamination, and environmental risk of potentially toxic elements (PTEs) in coastal sediments between Al-Jubail and Al-Khafji cities along the Arabian Gulf, Saudi Arabia, and documents the influence of background references applied in pollution indices. Thirty-two sediment samples were collected for analysis of Ni, Cu, Cr, As, Zn, Pb and Hg using ICP-AES. The ranges of PTEs (mg/kg) were in the following order: Cr (3.00–20.0), Ni (2.00–32.0), Zn (2.00–14.0), As (2.00–4.00), Pb (1.50–5.00), Cu (1.00–5.00), and Hg (0.50–1.00). The coastal sediments show severe enrichment with As and Hg, and no to minor enrichment and a low contamination with Cr, Cu, Cr, Zn, and Pb. Based on sediment quality guidelines, concentrations of Cu, Pb, Zn, As, and Cr do not represent a concern for benthic communities, while Ni and Hg show a risk for benthic communities in four and 17 sampled areas, respectively. Multivariate analysis indicated a geogenic source for Zn, Cr, Cu, Ni, and Pb, mixed natural and anthropogenic sources for As, and an anthropogenic source for Hg, mostly from oil pollution, sewage, and industrial effluents spreading near Al-Jubail industrial city.

Critical review on biogeochemical dynamics of mercury (Hg) and its abatement strategies

Mercury (Hg) is among the naturally occurring heavy metal with elemental, organic, and inorganic distributions in the environment. Being considered a global pollutant, high pools of Hg-emissions ranging from >6000 to 8000 Mg Hg/year get accumulated by the natural and anthropogenic activities in the atmosphere. These toxicants have high persistence, toxicity, and widespread contamination in the soil, water, and air resources. Hg accumulation inside the plant parts amplifies the traces of toxic elements in the linking food chains, leads to Hg exposure to humans, and acts as a potential genotoxic, neurotoxic and carcinogenic entity. However, excessive Hg levels are equally toxic to the plant system and severely disrupt the physiological and metabolic processes in plants. Thus, a plausible link between Hg-concentration and its biogeochemical behavior is highly imperative to analyze the plant-soil interactions. Therefore, it is requisite to bring these toxic contaminants in between the acceptable limits to safeguard the environment. Plants efficiently incorporate or absorb the bioavailable Hg from the soil thus a constructive understanding of Hg uptake, translocation/sequestration involving specific heavy metal transporters, and detoxification mechanisms are drawn. Whereas recent investigations in biological remediation of Hg provide insights into the potential associations between the plants and microbes. Furthermore, intense research on Hg-induced antioxidants, protein networks, metabolic mechanisms, and signaling pathways is required to understand these bioremediations techniques. This review sheds light on the mercury (Hg) sources, pollution, biogeochemical cycles, its uptake, translocation, and detoxification methods with respect to its molecular approaches in plants.

Mercury in multimedia system of Itacaiúnas Basin, Brazilian Amazon: An integrated approach to understand its distribution, origin, and ecological risk

This study presents the first integrated study on total Hg (THg) level in surface soil (SS), bottom soil (BS), stream sediments (SD), lake sediments (LS), stream water (SW), and lake water (LW) of Itacaiúnas River Watershed (IRW), Brazil to investigate the source and distribution of Hg in different environmental media considering contrasts of geological domains and sub-basins and its potential ecological and human risk. Hg content in most of the soils and sediments were above the upper crustal average values (56 μg/kg), however, when compared to the legal limits set by the Resolution CONAMA (Conselho Nacional de Meio Ambiente: soil 500 μg/kg; sediment 486 μg/kg), only 1 soil sample from Parauapebas sub-basin and 4 sediment samples from Violão Lake exceeded the limit. None of the SW and LW samples (<0.2 μg/L; CONAMA limit for Class II freshwater) are markedly contaminated by Hg. The SS and BS show similar contents and spatial distribution of Hg with higher contents being registered mostly in the Itacaiúnas and Parauapebas sub-basins, which are closely correlated with SD. This suggests that Hg levels are largely of geogenic origin and anthropogenic effect is highly limited. Principal Component Analysis (PCA) results show that Hg is strongly associated with total organic carbon (TOC), loss on ignition (LOI), and SO3, indicating organic matter as the main factor controlling the distribution of Hg and this is the major cause of accentuated Hg enrichment in lake sediments. The ecological risk index revealed a low pollution risk for most of the solid samples, except 11% LS and <1.5% SS and SD samples, which registered moderate risk. Health risk assessment indicated no adverse non-carcinogenic health effect on either adults and children in terms of Hg contamination. This information will be useful for Hg risk assessment in the Carajás region and future environmental research in this direction in the Amazonia.

A review of possible mechanisms for mercury migration in diagenesis: Clay to pyrite

Though sedimentary mercury in marine sediments has been regarded as a geological indicator of volcanic activity based on volcanism activity is the dominant natural source of Hg to the oceans, the influence of diagenesis on mercury cannot be dismissed. Marine mudstone has been selected to explore the migration of mercury from the syn-sedimentary stage to the diagenetic stage in this review. Marine mudstones undergo a series of significant transformation processes, including the illitization of smectite and the formation of framboidal pyrite aggregates during the diagenetic stage. This process makes the adsorption capacity of minerals change significantly that clay minerals are weakened, while pyrites are enhanced. In this reason, it is inferred that the sedimentary mercury may re-migrate from clay minerals to pyrite. This at least means that the indication of volcanic activity by mercury enrichment in marine mudstone need to be re-evaluated.

Atmospheric wet deposition of mercury in urban Jinan, eastern China: Speciation, scavenging process and potential sources

Understanding the speciation and related influence factors of Hg in wet deposition is important to predict the fate and transport of mercury in the atmosphere. In this study, event-based samples of rainwater were collected for one year in Jinan, a northern city in eastern China. The volume-weighted mean concentration of total mercury (THg) in rainwater was 34.8 ng L−1, comparable to levels in some inland cities in China and were significantly higher than those in North America, Korea and Japan. Most of the Hg in rainwater was associated with particulates, accounted for 15.2–92.9% of THg with a mean of 66.9%, which might be attributed to the scavenging effects of high particulate-bound mercury concentrations in ambient air in urban Jinan. Dissolved mercury (DHg) accounted for 33.1% of THg, in which Hg(OH)2, HgClOH, HgCl2 and Hg(NH3)22+ are the dominant species based on the chemical equilibrium modeling simulations. THg concentrations in rainwater decreased as the rainfall amount increased owing to the dilution effect and 5 mm rainfall might be a threshold for the full wash-out capability of atmospheric Hg. For a continuous rain event, the proportion of DHg in THg could increase from 7.1% to 84.8% with the rainfall processing, especially for the species of HgClOH and HgCl2 under the influence of rainwater pH. Positive matrix factorization (PMF) analysis suggested that the major sources of Hg in rainwater were combustion emissions, marine sources, industrial emissions, as well as complexation process, which contributed to 51.4%, 24.7%, 12.2%, and 11.7% of the THg, respectively. For the specific species, the main sources varied with different Hg species, in which combustion emissions contributed one third to one half of each species sum to particulate mercury (PHg), HgClOH, HgCl2, HgBrOH and HgBrCl followed by marine sources and industrial emissions. Cluster analysis of backward trajectories revealed that polluted air masses, transported from southeast Shandong, Anhui and Jiangsu Provinces, as well as Beijing-Tianjin-Hebei region, contributed to high Hg concentration in rainwater in Jinan.

Mercury contamination in the water and sediments of a typical inland river – Lake basin in China: Occurrence, sources, migration and risk assessment

In the area affected by non-ferrous metal mining activities, mercury (Hg) contamination in the water and sediments posed potential risks to ecology and human health. In this study, river water and sediment samples were collected in the Zijiang river - South Dongting Lake basin to analyze Hg residues, identify potential Hg sources and evaluate the ecological and health risks posed by Hg contamination. In this study, the average concentrations of THg, PHg, DHg and DMeHg in river water were 38.05 ± 27.13 ng/L, 25.18 ± 26.83 ng/L, 12.88 ± 9.64 ng/L and 0.29 ± 0.07 ng/L, respectively. The THg and MeHg contents in sediments were 234.24 ± 152.93 µg/kg and 0.48 ± 0.16 µg/kg, respectively. The more enrichment of Hg in sediments was observed in the Zijiang River than in the South Dongting Lake, especially in the upstream and midstream regions. Two potential Hg sources in the basin were identified by correlation matrix, principal component analysis (PCA) and positive matrix factorization (PMF) model. The comparable Hg flux with other rivers worldwide was found in the Zijiang River (0.53 Mg/y). Furthermore, it was found by the delayed geochemical hazard (DGH) model that the ecological risk of Hg was more significant in the Zijiang River with more frequent transformation pathways. For different populations, the health risk values caused by Hg were all lower than the USEPA’s guideline value. This study provided sound evidence for further control of Hg contamination.

Water Quality Assessment and Environmental Impact of Heavy Metals in the Red Sea Coastal Seawater of Yanbu, Saudi Arabia

The Yanbu industrial city along the Red Sea coast includes industries associated with crude oil and natural gas production and refining and support industries that produce manufactured goods for domestic and/or internal consumption. This study investigates the potential environmental impact and the possible sources of heavy metals (HMs), and it evaluates the quality of coastal surface seawater in the vicinity of Yanbu, along the Red Sea coast of Saudi Arabia. Thirty seawater samples have been collected and analyzed using an inductively coupled plasma mass spectrometer (ICP-MS) in order to determine the concentration values of Fe, Cr, Pb, Sb, Mn, Cu, Zn, Al, Ni, As, Cd, Co, and Hg. Reported HMs averages (μg/L) are in the following sequence: Ni (4.424) &gt; As (4.297) &gt; Cu (2.447) &gt; Zn (1.667) &gt; Al (1.133) &gt; Fe (0.983) &gt; Cr (0.723) &gt; Mn (0.328) &gt; Cd (0.309) &gt; Pb (0.276) &gt; Sb (0.238) &gt; Co (0.144) &gt; Hg (0.058). The contamination index (Cd) showed low contamination levels in all of the analyzed samples, whereas the index of heavy metal pollution (HPI) revealed medium contamination levels in 28 samples and low levels in two samples. Reported high HMs variations within samples are attributed to the multiplication of sources. The statistical analyses indicated anthropogenic sources for Cd, Co, Hg, Zn, and Ni, which may have originated from industrial, farming, or fishing activities around Yanbu city, while the remaining metals might be originated from combined lithogenic and human sources.

Terrestrial rather than volcanic mercury inputs to the Yangtze Platform (South China) during the Ordovician-Silurian transition

The Hg proxy has been used to infer a close relationship between volcanism and the ‘Big Five’ Phanerozoic mass extinctions. However, because of conflicting interpretations of Hg data, this relationship remains in debate for the Late Ordovician mass extinction (LOME). In this study, three sections (Datianba, Shuanghe and YY1), located in shallow to deep shelf settings, were chosen for investigation of the Hg cycle on the Yangtze Platform during the Ordovician-Silurian transition (OST). Our results show that sulfur-normalized Hg concentrations (Hg/TS, TS: total sulfur) are the best proxy for assessing Hg anomalies in these sections due to Hg being hosted mainly by sulfide minerals. The Hg/TS profiles of the three study sections exhibit no enhanced Hg loading of a potential volcanic origin. Differing Al-Hg relationships among the study sections imply different Hg sources, with dominantly terrigenous Hg at Datianba and hydrogenous (seawater-derived) Hg at Shuanghe and YY1. This inference is supported by contrasting near-zero to weakly negative Δ199Hg values at Datianba versus positive Δ199Hg values at Shuanghe. These findings demonstrate the influence of terrigenously sourced Hg on Upper Ordovician sediments of the Yangtze Platform, and, in conjunction with the non-correlatability of Hg anomalies between the study sections and their lack of a stratigraphic relationship to bentonites, they do not support a relationship between the LOME and large igneous province (LIP) or arc volcanism in the South China region during the OST.

Influence of Human Activity on Hg Transportation

Hg pollutes the environment, living organisms, and humans; hence, studying Hg content is essential for human health security. Using the dataset in May, September, and October, the Hg content, horizontal distribution, sources and transportation paths in the waters of Jiaozhou Bay were easily determined. These results indicate that the Hg content changing range in the waters in May, September and October was 0.015-0.150 μg/L, corresponding to the national seawater quality standards of Class I and Class II. The Hg content in the water body mainly arises from two sources, the transportation of rivers and offshore ocean currents. It from rivers' offshore ocean currents was 0.019-0.150 μg/L and 0.020 μg/L, respectively. Among them, the transportation of rivers includes the transportation of Haibo River, Licun River and Loushan River. So, a model block diagram has been built to unveil Hg contents and its different paths during the transportation to Jiaozhou Bay. Thus, it becomes easy to quantitively determine the migration process of Hg content through human activities to the ocean and rivers. Hg's different paths and contents reveal four rules for entering Jiaozhou Bay. In May, the offshore ocean currents and Haibo River did not affect by Hg pollution. In September, the Laoshan River was not polluted by it. In October, the Licun River was not, while the Haibo River exhibited light Hg pollution. When the Hg content transported by rivers was relatively low, it by offshore ocean currents became visible. From May to October, three rivers were transporting Hg content. Hg mildly polluted only one river in October, depicting that human activity is a key concern for environmental protection. It discharged by humans to land was relatively low, meanwhile only once was river transportation slightly polluted by it.

Risk Assessment of Potentially Toxic Elements in Agricultural Soils of Al-Ahsa Oasis, Saudi Arabia

Contamination of soil with potentially toxic elements (PTEs) is receiving great attention worldwide due to its apparent toxicity and hazards to local residents. The assessments of soil PTE distribution, sources, and environmental risks are, therefore, the first steps of high-efficiency pollutant degradation and sustainable utilization. The current study used a variety of contamination indicators and multivariate methods to evaluate the environmental risk of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in Al-Ahsa soils in eastern Saudi Arabia. For analysis, 30 surface soil samples were collected from palm fields irrigated with groundwater and treated sewage water. Landsat images of Al-Ahsa indicated an increase in the total vegetative area and the residential area, and a decrease in the bare land area from 1985 to 2021. The average concentrations of PTEs (mg/kg−1) were lower than the maximum admissible concentrations and had the following decreasing order: Zn (54.43) &gt; Cr (28.67) &gt; Ni (14.53) &gt; Cu (10.83) &gt; Pb (5.23) &gt; As (2.27) &gt; Hg (0.35) &gt; Cd (0.26). The enrichment factor (EF) findings confirmed that the Al-Ahsa soil is significantly enriched with Hg, moderately to severely enriched with As, and moderately enriched with Cd. The potential ecological risk index (RI) demonstrates a moderate ecological risk, with only certain parts presenting a high risk. The different PTE levels in agricultural soils may be caused partly by the various qualities of groundwater that originate from various aquifers and sewage-treated water. The results of a multivariate analysis showed that most of the anthropogenic sources of Hg, As, and Cd may come from using a lot of fertilizers and insecticides. Levels of the remaining PTEs indicated natural sources from earth crust materials.

Large extent of mercury stable isotope fractionation in contaminated stream sediments induced by changes of mercury binding forms

Mercury (Hg) release from contaminated legacy sites is a large contributor to riverine ecosystems and can represent a significant local and regional environmental issue even long after the initial site contamination. Understanding processes of in-stream species transformation is therefore important to assess the fate and bioavailability of the released Hg. In this study, we investigated in-stream Hg transformation processes with analyses of Hg binding forms and Hg stable isotopes. Stream sediments were collected downstream of a former kyanization facility (Black Forest, SW Germany), where highly soluble Hg(II)-chloride (HgCl2) was used as an anti-fouling agent to treat timber. Exfiltration of partly anoxic, contaminated groundwater with Hg concentrations of up to 700 μg L−1 into the adjacent Gutach stream is the main source of Hg to sediments. Total Hg concentrations in the stream bottom sediments (&amp;lt;2 mm) ranged from background values of 6.3 µg kg−1 upstream of the contaminated site to 77 mg kg−1 near the location of exfiltration of contaminated groundwater. A five-step sequential extraction procedure and Hg pyrolytic thermal desorption (PTD) analyses indicated changes in Hg binding forms in the sediments along the flow path towards a higher proportion of organically bound Hg. A large shift towards negative δ202Hg values was observed downstream of the contaminated site (change of ≈2‰) along with a minor offset in mass-independent fractionation. Binary mixing models based on Hg isotope ratios using one industrial and different natural background endmembers were tested to estimate their respective contribution of Hg to the sediments but failed to produce plausible allocations. Based on the observed changes in isotopic composition, total Hg concentrations and Hg binding forms, we propose that the large extent of fractionation observed in downstream sediments is the result of a combination of kinetic isotope effects during sorption, redistribution of Hg within the sediment and the preferential transport of Hg associated with the sediment fine fraction. These results highlight the importance of transformation processes when assessing the sources and fate of Hg in environmental systems and show limitations of using simple mixing models based on Hg stable isotopes.

Nano mercury selenide as a source of mercury for rice

Mercury (Hg) is a persistent and toxic metal while mercury selenide (HgSe) is generally considered as the environmental sink of Hg in its biogeochemical cycle. Recent studies found nano-sized HgSe (nano-HgSe) could be transformed by certain bacteria. This raises safety concerns about the application of selenium (Se) to curb Hg contamination in farmlands. Therefore, hydroponic experiments were performed in which rice plants were cultured with different concentrations of nano-HgSe and micro-sized HgSe (micro-HgSe) to explore their bioavailability and toxicity. It was found that both nano-HgSe and micro-HgSe did not affect the germination of rice seeds but affected the growth of rice seedlings. However, nano-HgSe could be more readily absorbed by roots and transferred to the aboveground parts compared to micro-HgSe. The highest Hg and Se levels were found to be 5255.67 ± 2496.14 μg/g and 1743.75 ± 61.87 μg/g, respectively in roots when exposed to 5000 mg/L nano-HgSe. Besides, small portion (1.2%) of methylmercury (MeHg) to total Hg was found accumulated in rice stem when exposed to 100 mg/L nano-HgSe, suggesting that nano-HgSe could be decomposed. Furthermore, nano-HgSe exposure brought oxidative damage to rice with decreased chlorophyll content and GSH-Px activity. In all, nano-HgSe was found to be more absorbable, transportable and methylated in rice plant compared to micro-HgSe. This suggests that although Se application in Hg contaminated farmland is an effective way to reduce the bioavailability of Hg, the risk of the possible remobilization of HgSe should not be neglected. Besides, the finding that nano-HgSe can act as an environmental source of Hg for plants deepens the understanding of biogeochemical cycle of Hg. More works are required to study the factors affecting the formation of nano-HgSe in the environment and the mechanisms of Hg methylation in rice plants after exposure to nano-HgSe.

Mercury Stable Isotope Composition of Lichens and Mosses from Northern Eurasia Reveals Hg Deposition Pathways and Sources

Mercury (Hg) concentrations in lichens and mosses can be used as surrogates for atmospheric Hg deposition to continental surfaces. In this study, we collected and analyzed Hg concentrations (n = 334) and isotopic composition (n = 67) of epiphytic tree lichens and terricolous lichens and mosses from remote locations across the Eurasian Arctic and sub-Arctic (50 to 72° N, 30 to 180° E). The total Hg (THg) concentrations ranged from 13 to 7700 ng g–1. Epiphytic tree lichens had significantly higher median THg levels (243 ng g–1) than terricolous lichens (35 ng g–1) and mosses (74 ng g–1). THg is substantially higher in both tree lichens and terricolous lichens near the Arctic Ocean shore and up to 300 km inland. The combined δ202Hg, Δ199Hg, and Δ200Hg signatures suggest that the elevated coastal Hg levels are delivered by marine air masses rich in gaseous and particulate-oxidized HgII forms, such as HgBr2. Similar to other vegetation Hg isotope studies, inland terricolous lichen and moss Δ200Hg are near zero, indicating a dominant (63%) atmospheric Hg0 origin followed by HgII wet and dry deposition. Inland tree lichens carry a more positive Δ200Hg of 0.15‰, similar to the atmospheric HgII end-member, suggesting that they preferentially accumulate HgII wet and dry deposition compared to colocated terricolous lichens. Mosses from the European sub-Arctic show a low δ202Hg of −3.1‰, which we speculate to result from regional soil Hg0 emissions that are recaptured by mosses. Overall, the Hg isotope variability of mosses and lichens reveals latitudinal gradients in Hg deposition pathways and identifies preferential Hg0 or HgII uptake.

Mercury Sources, Emissions, Distribution and Bioavailability along an Estuarine Gradient under Semiarid Conditions in Northeast Brazil

In the semiarid coast of northeast Brazil, climate change and changes in land use in drainage basins affect river hydrodynamics and hydrochemistry, modifying the estuarine environment and its biogeochemistry and increasing the mobilization of mercury (Hg). This is particularly relevant to the largest semiarid-encroached basin of the region, the Jaguaribe River. Major Hg sources to the Jaguaribe estuary are solid waste disposal, sewage and shrimp farming, the latter emitting effluents directly into the estuary. Total annual emission reaches 300 kg. In that estuary, the distribution of Hg in sediment and suspended particulate matter decreases seaward, whereas dissolved Hg concentrations increase sharply seaward, suggesting higher mobilization at the marine-influenced, mangrove-dominated portion of the estuary, mostly in the dry season. Concentrations of Hg in rooted macrophytes respond to Hg concentrations in sediment, being higher in the fluvial endmember of the estuary, whereas in floating aquatic macrophytes, Hg concentrations followed dissolved Hg concentrations in water and were also higher in the dry season. Animals (fish and crustaceans) also showed higher concentrations and bioaccumulation in the marine-influenced portion of the estuary. The variability of Hg concentrations in plants and sediments agrees with continental sources of Hg. However, Hg fractionation in water and contents in the animals respond to higher Hg availability in the marine-dominated end of the estuary. The results suggest that the impact of anthropogenic sources on Hg bioavailability is modulated by regional and global environmental changes and results from a conjunction of biological, ecological and hydrological characteristics. Finally, increasing aridity due to global warming, observed in northeast Brazil, as well as in other semiarid littorals worldwide, in addition to increased water overuse, augment Hg bioavailability and environmental risk and exposure of the local biota and the tradition of human populations exploiting the estuary's biological resources.

Sonochemical oxidation and stabilization of liquid elemental mercury in water and soil

Over 3000 mercury (Hg)-contaminated sites worldwide contain liquid metallic Hg [Hg(0)l] representing a continuous source of elemental Hg(0) in the environment through volatilization and solubilization in water. Currently, there are few effective treatment technologies available to remove or sequester Hg(0)l in situ. We investigated sonochemical treatments coupled with complexing agents, polysulfide and sulfide, in oxidizing Hg(0)l and stabilizing Hg in water, soil and quartz sand. Results indicate that sonication is highly effective in breaking up and oxidizing liquid Hg(0)l beads via acoustic cavitation, particularly in the presence of polysulfide. Without complexing agents, sonication caused only minor oxidation of Hg(0)l but increased headspace gaseous Hg(0)g and dissolved Hg(0)aq in water. However, the presence of polysulfide essentially stopped Hg(0) volatilization and solubilization. As a charged polymer, polysulfide was more effective than sulfide in oxidizing Hg(0)l and subsequently stabilizing the precipitated metacinnabar (β-HgS) nanocrystals. Sonochemical treatments with sulfide yielded incomplete oxidation of Hg(0)l, likely resulting from the formation of HgS coatings on the dispersed µm-size Hg(0)l bead surfaces. Sonication with polysulfide also resulted in rapid oxidation of Hg(0)l and precipitation of HgS in quartz sand and in the Hg(0)l-contaminated soil. This research indicates that sonochemical treatment with polysulfide could be an effective means in rapidly converting Hg(0)l to insoluble HgS precipitates in water and sediments, thereby preventing its further emission and release to the environment. We suggest that future studies are performed to confirm its technical feasibility and treatment efficacy for remediation applications.

Enrichment of mercury in the Lower Cambrian sedimentary successions by submarine hydrothermal venting

• Widespread sedimentary Hg enrichments in the Early Cambrian can be attributed to periodic hydrothermal ventilation. • Prevailing hydrothermal ventilation was an important source of Hg in sediments in the Early Cambrian. • The accumulation of Hg in sediments may be more effective in euxinic environments. Although extremely high Hg contents are known in the Lower Cambrian sedimentary successions, the extent and spatial-temporal distribution of sedimentary Hg anomalies in these successions remain unclear. Here, we report concentrations of Hg, total organic carbon (TOC), total sulfur (TS), and major and rare earth elements of the Lower Cambrian (∼525 Ma) sedimentary rocks at the Dongxihe section in the interior of the Yangtze Platform, South China. We investigated the sedimentary Hg enrichment mechanism and the spatial-temporal fluctuations of Hg in the Lower Cambrian and compiled published Hg (Hg/TOC) data from the Upper Neoproterozoic to the Lower Cambrian to trace the potential Hg sources. Our study verified that hydrothermal vents provide an excess Hg source for the sedimentary Hg enrichment in the Dongxihe section, which is supported by the positive Eu anomaly and major element. The major elements show more Fe and Mn enrichment in the upper part than the lower part, indicating more hydrothermal contribution in the upper part. Additionally, the records of the spatial-temporal distribution of Hg show that most of the sections (including shelf, slope, and basin) in South China show strong sedimentary Hg enrichment, which can be attributed to widespread hydrothermal venting. By reconstructing fluctuations of Hg during the Late Neoproterozoic to the Early Cambrian, we proposed that in the context of the Gondwana continent assembly, the prevalent hydrothermal ventilation event during the Early Cambrian not only induced the abnormal enrichment of sedimentary Hg but also played a crucial role in shaping the marine environment and ecosystem during this period.

Assessment and source apportionment of toxic metal in soils using integrated positive matrix factorization and Bayesian maximum entropy: A case study in Z county, southeastern China

Soil pollution by toxic metals has become an important environmental problem over the last several decades. Because of environmental factor variation, specific spatial patterns of pollution and sources exist. However, commonly used methods rarely take natural spatial heterogeneity into account. Positive matrix factorization and Bayesian maximum entropy models combined with specific environmental factors were proposed for quantitative source apportionment to account for spatial heterogeneity. The proposed method was implemented in a region located in southeastern China using dense samples (3627 total samples containing Cd, Hg, As, Pb, Cr, Cu, Zn and Ni data). The results showed that more than one-fifth of soils in the northwest, north-central and southeast of the study region exhibited different degrees of integrated pollution. Cd, Cu and As were the main pollutants, with proportions that exceeded the national standards of 26%, 10% and 7%, respectively. In addition, Cd was the primary element responsible for ecological risk, and As was the greatest hazard to human health. Five main pollution sources were extracted: 72.11% of the toxic metal pollution could be ascribed to anthropogenic sources, and natural sources explained the remaining 27.89%. Traffic emissions (24.31%) consistent with the major road distribution were the main source of Pb and Zn, and atmospheric deposition during the coal combustion (18.04%) distributed across the study area, except for the southeastern mountain areas, was the main source of Hg. Agricultural activities (16.81%) distributed mainly in the north-central regions contributed the most to Cd and Cu, and industrial activities (12.95%) clustered in the northwestern areas contributed the most to As. In addition, natural sources were closely linked to Ni and Cr in the southeastern mountain areas.

Mercury Speciation, Distribution, and Potential Sources in Surface Waters of the Yangtze and Yellow River Source Basins of Tibetan Plateau During Wet Season

To understand the mercury (Hg) biogeochemical cycle in alpine regions under global warming, it is critical to identify the distribution and sources of Hg in aquatic ecosystems of the Tibet Plateau. The spatial distribution pattern and potential sources of Hg species including total mercury (THg), particulate mercury (PHg), and dissolved mercury (DHg) were investigated in surface waters of the Yangtze and Yellow River source basins during the wet season. The results showed that average ρ(DHg) in surface water of the Yangtze and Yellow River source basins were comparable[(2.96±1.26) ng·L-1 and (2.47±0.83) ng·L-1, respectively], whereas the average ρ(THg)[(10.69±11.14) ng·L-1] and ρ(PHg)[(8.46±11.41) ng·L-1] in the source basin of the Yangtze River were significantly higher than that in surface water of the Yellow River source basin[(3.37±2.03) ng·L-1 and (1.13±1.02) ng·L-1, respectively]. It is worth noting that the ecological risk of Hg in the study area was limited because of low Hg concentration and methylation level. In addition, the correlation analysis illustrated that the THg was mainly concentrated by PHg in the source basin of the Yangtze River. Specifically, the concentration variations in Hg were mainly affected by the input of glacier meltwater, soil erosion, and precipitation. By contrast, the main species of Hg in the source basin of the Yellow River was DHg, the distribution pattern of which was mainly controlled by DOC. Spatially, a significant negative correlation was found between ρ(PHg) and longitude in the source basin of the Yangtze River (R2=0.46, P<0.01). The spatial distribution differences of river slope and soil erosion intensity were identified as the key factors leading to the decreasing trend of ρ(PHg) and ρ(THg) along the river flow in the source basin of the Yangtze River. The results of the PMF model further demonstrated that in the surface waters of the source regions of the Yangtze and Yellow Rivers, 51.4% of Hg derived from long-distance atmospheric deposition, 38.8% from erosion of soil rock or sediment via stream flow, and 9.7% from soil runoff or seepage input.