An Integrated Model for Input and Migration of Mercury in Chinese Coastal Sediments

Quantifying the impact of anthropogenic emissions and aquatic environmental impacts on sedimentary mercury variations in a typical urban river

In urban and industrial regions, sedimentary mercury (Hg) serves as the crucial indicator for Hg pollution, posing potential risks to ecology and human health. The physicochemical processes of Hg in aquatic environments are influenced by various factors such as anthropogenic emissions and aquatic environmental impacts, making it challenging to quantify the drivers of total mercury (THg) variations. Here, we analyzed the spatiotemporal variations, quantified driving factors, and assessed accumulation risks of sedimentary THg from the mainstream of a typical urban river (Haihe River). THg in the urban region (37-3237 ng g-1) was significantly higher (t-test, p < 0.01) than in suburban (71-2317 ng g-1) and developing regions (156-916 ng g-1). The sedimentary THg in suburban and developing regions increased from 2003 to 2018, indicating the elevated atmospheric deposition of Hg. Together with the temperature, grain size of sediments, total organic carbon (TOC), the pH and salinity of water, 40 components of parent and substituted polycyclic aromatic hydrocarbons (PAHs) were first introduced to quantify the driver of sedimentary THg based on generalized additive model. Results showed that anthropogenic emissions, including three PAHs components (31%) and TOC (63%), accounted for 94% of sedimentary THg variations. The aquatic environmental impacts accounted for 5% of sedimentary THg variations. The geo-accumulation index of THg indicated moderate to heavy accumulation in the urban region. This study demonstrates that homologous pollutants such as PAHs can be used to trace sources and variations of Hg pollution, supporting their co-regulation as international conventions regulate pollutants.

Mercury abatement in the environment: Insights from industrial emissions and fates in the environment

Mercury's neurotoxic effects have prompted the development of advanced control and remediation methods to meet stringent measures for industries with high-mercury feedstocks. Industries with significant Hg emissions, including artisanal and small-scale gold mining (ASGM)-789.2 Mg year-1, coal combustion-564.1 Mg year-1, waste combustion-316.1 Mg year-1, cement production-224.5 Mg year-1, and non-ferrous metals smelting-204.1 Mg year-1, use oxidants and adsorbents capture Hg from waste streams. Oxidizing agents such as O3, Cl2, HCl, CaBr2, CaCl2, and NH4Cl oxidize Hg0 to Hg2+ for easier adsorption. To functionalize adsorbents, carbonaceous ones use S, SO2, and Na2S, metal-based adsorbents use dimercaprol, and polymer-based adsorbents are grafted with acrylonitrile and hydroxylamine hydrochloride. Adsorption capacities span 0.2-85.6 mg g-1 for carbonaceous, 0.5-14.8 mg g-1 for metal-based, and 168.1-1216 mg g-1 for polymer-based adsorbents. Assessing Hg contamination in soils and sediments uses bioindicators and stable isotopes. Remediation approaches include heat treatment, chemical stabilization and immobilization, and phytoremediation techniques when contamination exceeds thresholds. Achieving a substantially Hg-free ecosystem remains a formidable challenge, chiefly due to the ASGM industry, policy gaps, and Hg persistence. Nevertheless, improvements in adsorbent technologies hold potential.

Spatial and temporal variations in the pollution status and sources of mercury in the Jiaozhou bay

In the past few decades, mercury (Hg) discharged into the coastal bays of China has significantly increased; however, long-term trends regarding the pollution status and sources of Hg in these bays have yet to be clear. Focusing on this issue, surface sediments and core sediments were collected in the Jiaozhou Bay (JZB), a typical bay highly affected by human activities in China, to analyze the concentrations and stable isotopic composition of Hg. Total mercury (THg) concentrations in surface sediment varied from 7 to 163 ng/g, with higher levels located in the eastern JZB, possibly attributed to intensive industrial and population density. THg in sediment cores 14 and 20 displayed fluctuating increasing trends from 1936 to 2019, reflecting the deterioration of Hg pollution. In contrast, THg in sediment core 28 near the river mouth exhibited a declining trend, possibly due to the river dam construction. Using a stable isotope mixing model, contributions of various sources (atmospheric, riverine, and industrial emissions) to Hg in the JZB were estimated. The results showed that industrial emissions were the main source (over 50%) of mercury in the JZB in 2019. Sediment cores recorded an increase in industrial Hg due to early industrialization and Reform and Opening-up before 2000. In addition, sediment core 20 demonstrated a rise in the percentage of riverine Hg due to land reclamation at the bay's mouth during 2000-2007.

Impacts of autochthonous dissolved organic matter on the accumulation of methylmercury by phytoplankton and zooplankton in a eutrophic coastal ecosystem

The bioaccumulation of methylmercury (MeHg) within the pelagic food webs is a crucial determinant of the MeHg concentration in the organisms at higher trophic levels. Dissolved organic matter (DOM) is recognized for its influence on mercury (Hg) cycling in the aquatic environment because of its role in providing metabolic substrate for heterotrophic organism and serving as a strong ligand for MeHg. However, the impact of DOM on MeHg bioaccumulation in pelagic food chains remain controversial. Here, we explored MeHg bioaccumulation within a pelagic food web in China, in the eutrophic Bohai Sea and adjacent seas, covering a range of DOM concentrations and compositions. Our findings show that elevated concentrations of dissolved organic carbon (DOC) and phytoplankton biomass may contribute to a reduction in MeHg uptake by phytoplankton. Moreover, we observe that a higher level of autochthonous DOM in the water may result in more significant MeHg biomagnification in zooplankton. This can be explained by alterations in the structure of pelagic food webs and/or an increase in the direct consumption of DOM and particulate organic matter (POM) containing MeHg. Our study offers direct field monitoring evidence of dual roles played by DOM in regulating MeHg transfers from water to phytoplankton and zooplankton in coastal pelagic food webs. A thorough understanding of the intricate interactions is essential for a more comprehensive evaluation of ecological risks associated with MeHg exposure in coastal ecosystems.

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.

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.

Mercury stable isotopes in the ocean: Analytical methods, cycling, and application as tracers

Mercury (Hg) has seven stable isotopes that can be utilized to trace the sources of Hg and evaluate the importance of transport and transformation processes in the cycling of Hg in the environment. The ocean is an integral part of the Earth and plays an important role in the global mercury cycle. However, there is a lack of a systematic review of Hg stable isotopes in marine environments. This review is divided into four sections: a) advances in Hg stable isotope analysis, b) the isotope ratios of Hg in various marine environmental matrices (seawater, sediment, and organisms), c) processes governing stable Hg isotope ratios in the ocean, and d) application of Hg stable isotopes to understand biotic uptake and migration. Mercury isotopes have provided much useful information on marine Hg cycling that cannot be given by Hg concentrations alone. This includes (i) sources of Hg in coastal or estuarine environments, (ii) transformation pathways and mechanisms of different forms of Hg in marine environments, (iii) trophic levels and feeding guilds of marine fish, and (iv) migration/habitat changes of marine fish. With the improvement of methods for seawater Hg isotope analysis (especially species-specific methods) and the measurement of Hg isotope fractionation during natural biogeochemical processes in the ocean, Hg stable isotopes will advance our understanding of the marine Hg cycle in the future, e.g., mercury exchange at the sea-atmosphere interface and seawater-sediment interface, contributions of different water masses to Hg in the ocean, fractionation mechanisms of Hg and MeHg transformation in seawater.

Riverine input of suspended particulate matter controls distribution, partitioning and transport of mercury and methylmercury in the Yellow River Estuary

Riverine mercury (Hg) is the largest global source of Hg in coastal oceans. The Yellow River delivers the majority of Hg to the semi-enclosed Bohai Sea, where Hg contamination adversely affects the surrounding heavily populated provinces in northern China. Mercury distribution patterns in the river-estuary interacting area provides essential information to understand the riverine Hg transport and biogeochemical cycling of Hg in the estuary. Analyzing the spatial distributions of total- (THg) and methyl-Hg (MeHg) in the lower end of Yellow River (∼105 km) and adjacent estuary, we found the dominant role of suspended particulate matter (SPM) in Hg transport, with 99.1% and 86.3% of THg and MeHg being in particulate phase. The SPM dynamics, such as transport, retention, sorting and sedimentation, governs Hg transport with water flow and particle-water partition of Hg. While THg decreased along the water flow to the river mouth with the settlement of particulate THg (about 27.5% onto the riverbed and the rest entering the sea), MeHg and particulate MeHg increased by 110% and 117%, respectively. This study highlights the distinct patterns in THg and MeHg distribution and transport and suggests potential Hg methylation and external MeHg input in the river-estuary mixed zone.

Seasonal variation in mercury and methylmercury production in vegetated sediment in the Dongtan wetlands of the Yangtze River Estuary, China

The seasonal cycling of mercury (Hg) in vegetated sediments in the Dongtan wetlands of the Yangtze River Estuary were determined, and microcosm incubation experiments were conducted to evaluate methylmercury (MeHg) production after Hg input. The results showed that the seasonal variations of total Hg and MeHg were very different. The enhanced activity of methylating bacteria could have been the main contributor to the elevated MeHg in the upper surface layer (0-12 cm), which was supported by the higher copy numbers of the hgcA gene in the surface sediment and the MeHg increase during sediment incubation following litterfall addition. Moreover, the incubation results showed that Hg addition greatly increased net MeHg production and that this increase remained under suboxic conditions, suggesting that the potential health risk of Hg in estuarine wetlands could exist for a long time under changing redox conditions.

Combining of C, N and specific Hg stable isotopes to track bioaccumulation of monomethylmercury in coastal and freshwater seafood

Human exposure to monomethylmercury (MMHg) through seafood consumption is a global concern. This study investigates the potential sources and processes of MMHg in seafood of coastal and freshwater areas through combing of δ¹³C, δ¹⁵N, and specific Hg (including MMHg and inorganic Hg (IHg)) isotopes. The results showed that δ¹³C and δ¹⁵N values exhibit different patterns in coastal and freshwater species. Δ¹⁹⁹Hg_MMHg/δ²⁰²Hg_MMHg values suggested that coastal and freshwater seafood undergo similar aqueous MMHg photodegradation processes. The Δ¹⁹⁹Hg_MMHg values could distinguish that, coastal fish absorb MMHg from water column whereas coastal shellfish absorb MMHg mainly from sediment. The positive values of Δ¹⁹⁹Hg_IHg in seafood could reflect in vivo MMHg demethylation and IHg reabsorption. Positive correlation between δ¹⁵N and Δ¹⁹⁹Hg_IHg indicated that aquatic organisms in various trophic levels may have different MMHg demethylation efficiency. We proposed that combining of multiple isotopes can provide overall profiles on aquatic MMHg biogeochemical cycle and bioaccumulation.

Reclaimable MoS2 Sponge Absorbent for Drinking Water Purification Driven by Solar Energy

With the fast development of modern industries, scarcity of freshwater resources caused by heavy metal pollution (i.e., Hg²⁺) has become a severe issue for human beings. Herein, a 3D-MoS₂ sponge as an excellent absorbent is fabricated for mercury removal due to its multidimensional adsorption pathways, which decreases the biomagnification effect of methylmercury in water bodies. Furthermore, a secondary water purification strategy is employed to harvest drinkable water with the exhausted adsorbents, thus alleviating the crisis of drinking water shortage. Compared to the conventional landfill treatment, the exhausted MoS₂ sponge absorbents are further functionalized with a poly(ethylene glycol) (PEG) layer to prevent the heavy metals from leaking and enhance the hydrophilicity for photothermal conversion. The fabricated evaporator displays excellent evaporation rates of ∼1.45 kg m^-2 h^-1 under sunlight irradiation and produces freshwater with Hg²⁺ under the WHO drinking water standard at 0.001 mg L^-1. These results not only assist in avoiding the biodeposition effect of mercury in water but also provide an environment-friendly strategy to recycle hazardous adsorbents for water purification.

Elucidating sources of mercury in the west coast of Korea and the Chinese marginal seas using mercury stable isotopes

Nearshore systems play an important role as mercury (Hg) sources to the open ocean and to human health via fish consumption. The nearshore system along East Asia is of particular concern given the rapid industrialization, which contributes to significant anthropogenic Hg emissions and releases. We used Hg stable isotopes to characterize Hg sources in the sediment and fish along the west coast of Korea, located at the northeast of the East China Sea. The Hg isotope ratios of the west coast sediments (δ²⁰²Hg; -0.89 to -0.27‰, Δ¹⁹⁹Hg; -0.04 to 0.14‰) were statistically similar with other nearshore sediments (δ²⁰²Hg; -0.99 to -0.30‰, Δ¹⁹⁹Hg; -0.04 to 0.19‰) and overlapped with the industrial Hg source end-member (δ²⁰²Hg; -0.5‰, Δ¹⁹⁹Hg; 0.01‰) estimated from the Chinese marginal seas. Using a ternary mixing model, we estimated that industrial Hg sources contribute 83-97% in the west coast of Korea, and riverine and atmospheric Hg sources play minor roles in the Korean west coast and the Chinese marginal seas. The comparison between Hg isotope ratios of the sediment and nearshore fish revealed that the fish in the most west coast sites are exposed to MeHg produced in the sediment. At a few southwest coast sites, external MeHg produced in rivers and the open ocean water column appears to be more important as a source in fish. This is supported by much higher δ²⁰²Hg (0.74‰; similar to oceanic fish) and lower δ²⁰²Hg (-0.71‰; similar to riverine sources) compared to fish collected from other west coast sites influenced by sedimentary MeHg. The substantial Hg contributions from industrial activities suggest the national policies regulating anthropogenic Hg releases can directly mitigate human Hg exposure originating via local fish consumption. This study contributes to the growing regional and global inventories of Hg fluxes and sources exported into coastal oceans.

Highly Resolved Inventory of Mercury Release to Water from Anthropogenic Sources in China

This study developed an up-to-date and point-source-based inventory of mercury (Hg) releases to water in China by applying probabilistic release factors that combined industry removal efficiencies, reuse of reclaimed water, and receiving water types. In 2017, the national mercury release to water was estimated to be 50 (35-66) tons, in which 47%, 8%, 7%, and 25% were from nonferrous metal smelting, vinyl chloride monomer (VCM) production, coal-fired boilers, and domestic sewage, respectively. Approximately 95% of mercury was released to inland rivers, and the rest was discharged to lakes or coastal water. The significant sources were identified based on their mercury releases to water. The control of mercury release to water in China shall focus on zinc smelting plants, municipal sewage treatment plants, and the VCM production process. For zinc smelting plants, China can tighten the limit of mercury concentration in discharged wastewater and combine Hg-catcher device in traditional integrated treatment. For municipal sewage treatment plants and the VCM production process, promoting processes of Hg-free production can reduce mercury inputs at the source. Our study provides insights for other parties to identify the relevant sources of mercury release to water and to conduct control measures, so as to promote the global convention implementation.

Distribution of mercury isotope signatures in Yundang Lagoon, Xiamen, China, after long-term interventions

Isotope signatures of mercury (Hg) were determined for Hg fractions in seawater, sediments, porewaters, core sediments and fish from the Yundang Lagoon, Xiamen, China. Sequential extraction was used to extract Hg fractions in sediments and the purge-trap method was used to preconcentrate Hg in seawater. A large variation in mass dependent fractionation (δ²⁰²Hg: -2.50‰ to -0.36‰) was observed in the lagoon. Seawater and fish samples showed positive mass-independent fractionation (Δ¹⁹⁹Hg: -0.06‰-0.45‰), while most of sediment and porewater samples displayed insignificant mass-independent fractionation (Δ¹⁹⁹Hg: -0.10‰-0.07‰). Ancillary parameters (total organic carbon, sulfide, pH, Eh, water content and grain size) were also measured in the sediments to investigate correlations with Hg isotopes. Three sources (domestic sewage, sediments and atmospheric deposition) were identified as the main sources of Hg in the lagoon seawater. Photochemical reaction was the main process causing isotope fractionation in seawater. Through Hg partitioning and deposition, light isotopes were enriched from dissolved Hg to particulate Hg, then to sediments, and then to porewaters. Finally, Hg isotope signatures were used to identify the Hg sources and fractionation processes in core sediments from different depths. Our results demonstrate that Hg isotopes are powerful tools for tracing Hg sources and arriving at a better understanding of Hg biogeochemical cycling in the lagoon after long-term interventions.

Spatio-Temporal Distribution of Environmental Health Risk of Heavy Metals in Industrial Wastewater of China during 1999-2018

In recent decades, environmental health risk caused by heavy metals in industrial wastewater (EHR-IHM) has become a serious issue globally, especially for China. Given the spatial difference of heavy metal emissions, hydrogeography, population distribution, etc., it is essential to estimate China's EHR-IHM from a high-resolution perspective. Based on the framework of USEtox, this study constructs an environmental health risk assessment method for heavy metals discharged from industrial wastewater by coupling the Pollutant Accumulation Model (PAM). This method also considers the process of heavy metal flows between upstream and downstream areas. Based on this constructed method, we investigate the spatio-temporal distribution of EHR-IHM of As, Cd, Cr(VI), Hg, and Pb in China from 1999 to 2018. Results showed that the EHR-IHM in China increased rapidly during 1999-2007 and decreased gradually during 2007-2018, with the highest Damage Level (DL) of 6.8 × 10⁴ disability-adjusted life years (DALY). As and Cr(VI) were the major heavy metal pollutants, which induced 58.9-70.6% and 23.9-36.2% of the total EHR-IHM, respectively. Intake of aquatic products was the dominant exposure route, accounting for over 84.1% of national EHR-IHM, followed by drinking water intake, accounting for 9.5-15.8%. Regarding spatial distribution, the regions with high EHR-IHM are mainly distributed in the middle-lower reaches of the Yangtze River, southeast coastal cities, Bohai Rim, etc.

The influence of legacy contamination on the transport and bioaccumulation of mercury within the Mobile River Basin

Past industrial use and subsequent release of mercury (Hg) into the environment have resulted in severe cases of legacy contamination that still influence contemporary Hg levels in biota. While the bioaccumulation of legacy Hg is commonly assessed via concentration measurements within fish tissue, this practice becomes difficult in regions of high productivity and methylmercury (MeHg) production, like the Mobile River Basin, Alabama in the southeastern United States. This study applied Hg stable isotope tracers to distinguish legacy Hg from regional deposition sources in sediments, waters, and fish within the Mobile River. Sediments and waters displayed differences in δ²⁰²Hg between industrial and background sites, which corresponded to drastic differences in Hg concentration. Sites that were affected by legacy Hg, as defined by δ²⁰²Hg, produced largemouth bass with lower MeHg content (59-70%) than those captured in the main rivers (>85%). Direct measurements of Hg isotopes and mathematical estimates of MeHg isotope pools in fish displayed similar distinctions between legacy and watershed sources as observed in other matrices. These results indicate that legacy Hg can accumulate directly into fish tissue as the inorganic species and may also be available for methylation within contaminated zones decades after the initial release.

Insights into Mercury Source Identification and Bioaccumulation Using Stable Isotope Approaches in the Hannibal Pool of the Ohio River, USA

Mercury contamination in river systems due to historic and current Hg releases is a persistent concern for both wildlife and human health. In larger rivers, like the Ohio River, USA, it is difficult to directly link Hg discharges to bioaccumulation due to the existence of multiple industrial Hg sources as well as the varied dietary and migratory habits of biota. To better understand how industrial effluent influences the cycling and bioaccumulation of Hg within the Ohio River, Hg stable isotope analysis was applied to various nonbiological and biological media. High Hg concentrations in suspended particulate matter suggest this vector was the largest contributor of Hg to the water column, and distinct Hg source signatures were observed in effluent particulates from different industrial processes, such as chlor-alkali activity (δ202 Hg = -0.52‰) and coal power plant discharge (δ202 Hg = -1.39‰). Despite this distinction, average sediments (δ202 Hg = -1.00 ± 0.23‰) showed intermediate isotopic signatures that suggest the accumulation of a mixed Hg source driven by multiple industrial discharges. Biota in the system were shown to have a conserved range of δ202 Hg and estimation approaches related these signatures back to particulate matter within Hannibal Pool. Mussels were found to conserve Hg isotopes signatures independently of food web drivers and served as ideal water column indicators of bioaccumulated Hg sources. This study highlights the complexity of Hg cycling within an industrialized river and shows that an isotope tracer approach can provide insight to water column sources of Hg. Integr Environ Assess Manag 2021;17:233-242. Published 2020. This article is a US Government work and is in the public domain in the USA.

Isotopic tracing of mercury sources in estuarine-inner shelf sediments of the East China Sea

Large river estuarine-inner shelf systems play an important role in the coastal biogeochemical cycling of heavy metals; however, the source-to-sink of mercury (Hg) in these environments remain poorly understood. In this study, the Hg isotopic composition of surface sediments in the Yangtze River Estuary (YRE) and inner shelf of the East China Sea (ECS) were examined to quantitatively track Hg sources in this region. We detected large spatial variation in δ²⁰²Hg (-1.88 to -0.29‰) and Δ¹⁹⁹Hg (-0.22 to 0.13‰) in sediments of the YRE-ECS inner shelf. The impact of sediment resuspension and transport from the YRE to the inner shelf of the ECS could have little effect on Hg isotopic composition, and the two regions shared similar Hg isotopic composition. An isotope-based triple mixing model further revealed major contributors to sediment Hg from industrial Hg discharge into water (51.8 ± 24.5%), soil Hg from surface runoff (29.2 ± 17.0%), and precipitation-derived atmospheric deposition Hg (19.1 ± 17.5%). The Hg isotopic compositions of the YRE sediments and other local river estuaries were similar to those of direct industrial Hg discharge, indicating that contaminated riverine discharge was the dominant Hg source for estuarine and adjacent shelf areas. Soil Hg delivered through surface runoff was the primary source of Hg to the coastal areas not near large river estuaries, whereas precipitation-derived atmospheric deposition had a greater influence on offshore sediment Hg content. Industrial Hg discharged to rivers had the highest mean depositional flux (35.0 ± 27.3 ng cm^-2 yr^-1) and mass inventory (25.6 t yr^-1), accounting for 77.4% of the total Hg variance. The findings of this study demonstrate that large rivers such as the Yangtze River can supply substantial amounts of industrial Hg to the estuary and adjacent shelf.

Mercury isotope variations within the marine food web of Chinese Bohai Sea: Implications for mercury sources and biogeochemical cycling

Mercury (Hg) speciation and isotopic compositions in a large-scale food web and seawater from Chinese Bohai Sea were analyzed to investigate methylmercury (MeHg) sources and Hg cycling. The biota showed ∼5‰ variation in mass dependent fractionation (MDF, -4.57 to 0.53‰ in δ²⁰²Hg) and mostly positive odd-isotope mass independent fractionation (odd-MIF, -0.01 to 1.21‰ in Δ¹⁹⁹Hg). Both MDF and odd-MIF in coastal biota showed significant correlations with their trophic levels and MeHg fractions, likely reflecting a preferential trophic transfer of MeHg with higher δ²⁰²Hg and Δ¹⁹⁹Hg than inorganic Hg. The MDF and odd-MIF of biota were largely affected by their feeding habits and living territories, and MeHg in pelagic food web was more photodegraded than in coastal food web (21-31% vs. 9-11%). From the Hg isotope signatures of pelagic biota and extrapolated coastal MeHg, we suggest that MeHg in the food webs was likely derived from sediments. Interestingly, we observed complementary even-MIF (mainly negative Δ²⁰⁰Hg of -0.36 to 0.08‰ and positive Δ²⁰⁴Hg of -0.05 to 0.82‰) in the biota and a significant linear slope of -0.5 for Δ²⁰⁰Hg/Δ²⁰⁴Hg. This leads us to speculate that atmospheric Hg⁰ is an important source to bioaccumulated MeHg, although the exact source-receptor relationships need further investigation.

The distribution and risk of mercury in Shenzhen mangroves, representative urban mangroves affected by human activities in China

Sediments were collected from urban mangroves in Shenzhen, China, including Shajing (SJ) and Xixiang (XX) featured with industrial district; Futian (FT) and Baguang (BG) featured with central business district and ecological preserve, respectively. Distributions, pollution levels and human health risks of Hg were explored. In both surface and vertical sediments, mean Hg concentration was highest in SJ mangrove, which may be due to its proximity to point-source discharge of Maozhou River in Pearl River Estuary, China. Sediment properties (pH, salinity, TOC and particle size) had limited impact on Hg accumulation due to their non-significant correlations. Geo-accumulation index, pollution load index, potential ecological risk index, and the ecological risk assessment code showed the highest ecological risk in SJ mangrove, followed by XX, FT, and BG mangroves. The assessment of human health risks showed that public experience little adverse health risk due to exposure to Hg polluted sediment in urban mangroves.

Accelerated screening of arsenic and selenium fractions and bioavailability in fly ash by microwave assistance

Huge amounts of fly ash (FA) can be annually produced in power plants. Fly ash always contains high levels of arsenic (As) and selenium (Se) due to the preconcentration of these two elements during coal combustion process. It would be much concerned to screen their fractions and potential environmental behaviors in fly ash for beneficial use and treatment. Fast and practical methods for this purpose are urgently needed. Two fast and effective microwave-assisted sequential extraction schemes (MASE) were developed for fast screening As and Se fractions in fly ash for the first time. The extraction parameters including microwave irradiation time, temperature and power energy were optimized by comparing the results from MASE and the conventional scheme (Wenzel method). The results indicate that the extraction efficiency of As and Se in various fractions can be significantly accelerated by microwave irradiation. The whole procedure operation time can be significantly reduced from 24.5 h to 44 min by microwave assistance compared with the conventional shaking schemes. The recoveries of As and Se in the various extracted fractions were all above 80% with relative standard deviations (RSDs) below 8%. The developed methods were further confirmed by the validation of the certified reference material GBW08401 and fly ash samples from six power plants. The developed MASE methods are practical and effective for fast screening arsenic and selenium fractions in fly ash samples.

Environmental applications of metal stable isotopes: Silver, mercury and zinc

With developments in multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), applications of metal stable isotopes received increasing attentions in the studies of source and fate of heavy metals in the environment. In light of the rapid progresses in this emerging field, we attempted to review the recent findings comprehensively in a way that environmental scientists can easily read. This review started with an introduction of basic terminologies in isotope geochemistry, followed with detailed descriptions of instrumentation and analytical procedures, and finally focused on the cases of three typical metal stable isotopes (Ag, Hg and Zn) to illustrate how they were applied to address environmental issues. Additionally, future perspectives on the applicability, opportunities, and limitations of metal stable isotope techniques as novel approaches in advancing environmental chemistry were discussed.