Mercury Isotopic Compositions Research Articles

Variation in the mercury concentration and stable isotope composition of atmospheric total suspended particles in Beijing, China

We investigated the effect of the temporary ban of local industrial activities during the Asia-Pacific Economic Cooperation (APEC) summit (4th–14th Nov 2014) in Beijing, China on total suspended particulate mercury (HgTSP) concentrations and isotope compositions. We measured Hg concentrations and isotope ratios in 33 TSP samples from central Beijing, including 21 samples collected from Jun 2012 to Apr 2014, and 12 samples collected from 14th Oct–19th Nov 2014. Volumetric concentrations of both TSP and HgTSP during the APEC summit were a factor of 2 lower than during the pre-APEC period, indicating substantial reductions in total particulate matter and HgTSP as a result of emissions controls. However, mass-normalized concentrations and mercury isotope ratios of HgTSP did not vary significantly between samples collected before, during, or after the APEC summit. These results show that local emissions are important sources of particle bound mercury (PBM) in Beijing and that their control can be used to immediately lower the volumetric concentration of HgTSP. They also indicate that a similarly complex mixture of sources contributed to PBM in Beijing before and during emissions controls were put in place and that PBM concentrations in Beijing are primarily controlled by emissions and secondarily by photoreduction.

Application of an Isotope Binary Mixing Model for Determination of Precise Mercury Isotopic Composition in Samples with Low Mercury Concentration.

An isotope binary mixing model was applied for high precision measurement of mercury isotope ratios in samples with low mercury concentrations by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). Standard addition was used to evaluate the precision and accuracy of the isotope composition calculations resulting from the isotope binary mixing model. A high, steady 202Hg signal of approximately 2.13 V was achieved, with the mercury concentration reaching 3 ng/mL. The isotopic composition of three standards (NIST SRM 1646a; NIST SRM 1575a; BCR 482) and natural samples were precisely determined. The standards and natural samples were diluted to low mercury concentrations (low to 0.90 ng/mL) and mixed with standard solutions (NIST SRM 3133) with high mercury concentrations (50 ng/mL); the isotopic compositions of low mercury concentration samples were calculated using an isotope binary mixing model after the isotopic compositions of the mixing solutions were measured. The results showed that the uncertainty of the calculated mercury isotopic compositions was in an acceptable range and the calculation isotope data were in good agreement with direct measurements. Our method allows the precise determination of mercury isotope composition in mercury solutions of concentrations (0.90 ng/mL) below the detection limit of the current system (3.00 ng/mL).

Changes in the mercury isotopic composition of sediments from a remote alpine lake in Wyoming, USA

Mercury (Hg) deposition from the atmosphere has increased dramatically since 1850 and Hg isotope records in lake sediments can be used to identify changes in the sources and cycling of Hg. We collected a sediment core from a remote lake (Lost Lake, Wyoming, USA) and measured vertical variation of Hg concentration and isotopic composition as well as 210Pb and 137Cs activities to establish a chronology. We also analyzed vegetation and soil samples from the watershed which has a small ratio of watershed area to lake surface area (2.06). The Hg flux remains constant from ~1350 to 1850 before increasing steadily to modern values that are approximately four times pre-1850 values. The modern Hg isotopic composition preserved in the sediments is distinct from the Hg isotopic composition of pre-1850 samples with both δ202Hg and Δ199Hg becoming progressively more positive through time, with shifts of +0.37‰ and +0.23‰ respectively. To explain temporal changes in δ202Hg, Δ199Hg, and Hg concentration in the core segments, we estimated a present-day atmospheric endmember based on precipitation and snow samples collected near Lost Lake. The observed change in Hg isotopic values through time cannot be explained solely by addition of anthropogenic Hg with the isotopic composition that has been estimated by others for global anthropogenic emissions. Instead, the isotope variation suggests that the relative importance of redox transformations, whether in the atmosphere, within the lake, or both, have changed since 1850.

Mercury isotopic compositions of mosses, conifer needles, and surface soils: Implications for mercury distribution and sources in Shergyla Mountain, Tibetan Plateau

Understanding the distribution and sources of mercury (Hg) in the Tibetan Plateau is of great value to study the long-range transport of Hg. Herein, the total Hg (THg) concentrations and the isotopic compositions of mosses, conifer needles, and surface soils collected from both slopes of the Shergyla Mountain of Tibetan Plateau were analyzed. The contents of THg in samples (except mosses on the eastern slope) were significantly positively correlated with altitude in both the western and eastern slopes, possibly caused by topographic factors. In contrast, Δ199Hg in samples was significantly negatively correlated with altitude. On the basis of Hg isotopic compositions, atmospheric Hg0 uptake was indicated as the primary accumulation pathway of Hg in mosses (Δ199Hg: −0.12 ± 0.09‰, −0.26 – 0.00‰, 1 SD, n = 10) and conifer needles (Δ199Hg: −0.21 ± 0.08‰, −0.36 – −0.11‰, 1 SD, n = 9). Moreover, the contributing fractions of atmospheric Hg0 to Hg in surface soils (Δ199Hg: −0.20 ± 0.07‰, −0.31 – −0.06‰, 1 SD, n = 17) increased with altitude and accounted for an average of 87 ± 9% in atmospheric sources. Due to the special geographic positions and environmental conditions of the Tibetan Plateau, the results of this study were essential for further understanding the long-range transport and global cycling of Hg.

Characteristics of Stable Mercury Isotopic Compositions in the Food Web of the Caohai Lake

Caohai Plateau Wetland is a National Nature Reserve. The characteristics of stable mercury isotopic compositions in the food web were studied by comprehensively analyzing the concentrations of Hg species (MeHg, THg), δ13 C, and δ15N, and the isotopic compositions of Hg in different aquatic organisms. The main results are as follows:all samples of the food web show mass-dependent fractionation (MDF) and mass-independent fractionation (MIF) and a negative δ202 Hg(-0.93‰±1.32‰, n=14)and positive △199 Hg(0.79‰±0.76‰, n=14). The δ199 Hg values are significantly positively correlated with δ15N (r=0.65, P<0.05) and the δ202 Hg values also exhibit a positive correlation with δ15N, except for Myriophyllum spicatum(δ15N=-1.88‰), indicating that the bioaccumulation of mercury leads to an enrichment with heavier isotopes. The △199 Hg values increase with δ15N(r=0.67, P<0.05). Nevertheless, the △199 Hg values correlate with% MeHg (r=0.58, P<0.05), indicating that the increase of the MIF level in the samples with the food web might be related to% MeHg.

An improved method for recovering and preconcentrating mercury in natural water samples for stable isotope analysis

A new method is developed to meet the criteria for precise and efficient measurements of mercury isotopic composition in various water samples.

Spatial distributions and sources of heavy metals in sediments of the Changjiang Estuary and its adjacent coastal areas based on mercury, lead and strontium isotopic compositions

The distribution, source and fate of the heavy metals mercury (Hg) and lead (Pb) in surface sediments from the East China Sea (ECS) were studied using mercury, lead and strontium (Sr) isotopic ratios. Hydrodynamic circulation and the sedimentary depositional process within the ECS were the dominant factors controlling the distribution and fate of heavy metals, referring from relationships of heavy metals (Hg and Pb) concentrations and total organic carbon (TOC) and clay contents. Spatial variations in Hg isotopic compositions (δ202Hg) were observed in the ECS, with δ202Hg ranging from −1.86 to −0.83‰ and Δ199Hg ranging from −0.07 to +0.26‰. The high δ202Hg values and relatively negative Δ199Hg values in estuarine and inner shelf sites indicated that the riverine inputs from Changjiang River played an important role in delivering Hg to ECS. In contrast, Hg isotopic signatures in outer shelf sediments had relatively low δ202Hg and positive Δ199Hg, implying that atmospheric Hg deposition could be a relatively dominant source for Hg. Using these Hg isotope compositions, the source attributions of sediments in ECS were estimated based on a triple mixing model, suggesting that river-dominated inputs, discharging pollutants from industrial sources, and atmospheric deposition could dominate in the occurrence and fate of Hg in surface sediments of ECS. Moreover, the results of Pb and Sr isotopic ratios in surface sediment samples and potential sources showed that the Pb accumulated in the ECS was mainly from background and anthropogenic sources, with the contribution rates of 45% and 55%, respectively.

Mercury vapor analyzer based on capillary lamp with natural mercury isotope composition in the transverse Zeeman effect: capabilities and prospects

A mercury-vapor analyzer which is based on a method of atomic absorption spectroscopy is proposed to operate in the atmospheric air. The source of emission used in the instrument is a low-pressure capillary lamp filled with mercury of natural isotope composition. Features of its emission spectrum are described under the transverse Zeeman effect in the vicinity of a resonance wavelength of 253.7 nm. The emission intensities π and the sums of σ components of this lamp are studied. The results of experimental investigations of the analyzer operating modes are presented, and systematic measurement errors are estimated (±30 ng/m3). Some options of improving the analyzer response are demonstrated.

Spatial and temporal variation in the isotopic composition of mercury in the South River, VA

Historic point source mercury (Hg) inputs from industrial processes on the South River (Waynesboro, Virginia) ended many decades ago, but sediment and surface water Hg concentrations remain elevated relative to the regional background. To understand Hg sources, mobility, and fate in the South River, we analyzed total Hg concentrations and Hg stable isotope compositions of streambed sediments, bank soils, suspended particles, filtered surface waters, and channel margin hyporheic zone pore waters. Hg isotopes allow for the identification of three distinct Hg end-member inputs to the South River, consisting of a regional background source and two isotopically distinct contaminant sources. Hydrologic conditions are demonstrated to have an influence on within-channel Hg isotope fractionation and Hg partitioning, with no observed isotopic discrimination between suspended particulate Hg and filtered surface water Hg during elevated flow conditions. Channel margin hyporheic zone porewaters had significantly higher δ202Hg values than surface waters (δ202Hg = −0.52 ± 0.44‰ and δ202Hg = −0.89 ± 0.20‰ respectively [mean ± 1SD]). A subset of porewaters exhibited mass independent fractionation signatures (Δ199Hg = 0.33 ± 0.06‰; Δ200Hg = 0.19 ± 0.03‰ [mean ± 1SD]) that are suggestive of a precipitation-derived origin for the dissolved Hg pool. Sediments from a floodplain profile were analyzed to explore the temporal variation in Hg isotopic composition within the South River, indicating brief excursions (up to δ202Hg = +0.61‰) from the average composition observed in modern samples (δ202Hg = −0.52 ± 0.09‰). By improving understanding of the spatial, temporal, and hydrologic conditions that contribute to variations in Hg isotopic composition, this study provides insights into the processes that control Hg isotopic end-member sources, Hg-loading to the channel during elevated flows, and Hg fate in the South River.

Development of a High-Resolution Laser Absorption Spectroscopy Method with Application to the Determination of Absolute Concentration of Gaseous Elemental Mercury in Air.

Isotope dilution-cold-vapor-inductively coupled plasma mass spectrometry (ID-CV-ICPMS) has become the primary standard for measurement of gaseous elemental mercury (GEM) mass concentration. However, quantitative mass spectrometry is challenging for several reasons including (1) the need for isotopic spiking with a standard reference material, (2) the requirement for bias-free passive sampling protocols, (3) the need for stable mass spectrometry interface design, and (4) the time and cost involved for gas sampling, sample processing, and instrument calibration. Here, we introduce a high-resolution laser absorption spectroscopy method that eliminates the need for sample-specific calibration standards or detailed analysis of sample treatment losses. This technique involves a tunable, single-frequency laser absorption spectrometer that measures isotopically resolved spectra of elemental mercury (Hg) spectra of 6 1S0 ← 6 3P1 intercombination transition near λ = 253.7 nm. Measured spectra are accurately modeled from first-principles using the Beer-Lambert law and Voigt line profiles combined with literature values for line positions, line shape parameters, and the spontaneous emission Einstein coefficient to obtain GEM mass concentration values. We present application of this method for the measurement of the equilibrium concentration of mercury vapor near room temperature. Three closed systems are considered: two-phase mixtures of liquid Hg and its vapor and binary two-phase mixtures of Hg-air and Hg-N2 near atmospheric pressure. Within the experimental relative standard uncertainty, 0.9-1.5% congruent values of the equilibrium Hg vapor concentration are obtained for the Hg-only, Hg-air, Hg-N2 systems, in confirmation with thermodynamic predictions. We also discuss detection limits and the potential of the present technique to serve as an absolute primary standard for measurements of gas-phase mercury concentration and isotopic composition.

Use of Mercury Isotopes to Quantify Mercury Exposure Sources in Inland Populations, China.

Mercury (Hg) isotopic compositions in hair and dietary sources from Wanshan (WS) Hg mining area, Guiyang (GY) urban area, and Changshun (CS) rural area were determined to identify the major Hg exposure sources of local residents. Rice and vegetables displayed low δ202Hg and small negative to zero Δ199Hg, and are isotopically distinguishable from fish which showed relatively higher δ202Hg and positive Δ199Hg. Distinct isotopic signatures were also observed for human hair from the three areas. Shifts of 2 to 3‰ in δ202Hg between hair and dietary sources confirmed mass dependent fractionation of Hg isotopes occurs during metabolic processes. Near zero Δ199Hg of hair from WS and CS suggested rice is the major exposure source. Positive Δ199Hg of hair from GY was likely caused by consumption of fish. A binary mixing model based on Δ199Hg showed that rice and fish consumption accounted for 59% and 41% of dietary Hg source for GY residents, respectively, whereas rice is the major source for WS and CS residents. The model output was validated by calculation of probable daily intake of Hg. Our study suggests that Hg isotopes can be a useful tracer for quantifying exposure sources and understanding metabolic processes of Hg in humans.

Mercury in litterfall and sediment using elemental and isotopic composition of carbon and nitrogen in the mangrove of Southeastern Brazil

Mercury and elemental and isotopic compositions of carbon and nitrogen were determined in litterfall and sediments from the mangrove of the Paraíba do Sul River, Rio de Janeiro, Brazil. Total mercury (THg) and monomethylmercury (MMHg) concentrations in sediment ranged from 33 to 123 ng g−1 and 0.20–1.38 ng g−1, respectively. The δ13C in sediment varied from −29.4 to −26.5‰ and from 2.4 to 5.8‰ in δ15N. The THg concentration in litterfall and its annual input to the mangrove was 21 ± 2 ng g−1 and 16 ± 4 μg m−2 for the species Laguncularia racemosa, 18 ± 1 ng g−1 and 17 ± 3 μg m−2 for Rhizophora mangle, and 53 ± 4 ng g−1 and 33 ± 4 μg m−2 for Avicennia germinans, respectively. The isotopic composition of leaf litter ranged from −28.6 to −26.9‰ for δ13C and 4.5–7.2‰ for δ15N. Both the highest annual Hg input via litterfall and highest sediment Hg concentration were observed in areas dominated by A. germinans. These results suggest that the rate of litterfall of plant species and the atmospheric deposition have played an important role in the Hg biogeochemical cycle in the mangrove ecosystem.

Mercury Stable Isotopes Discriminate Different Populations of European Seabass and Trace Potential Hg Sources around Europe.

Our study reports the first data on mercury (Hg) isotope composition in marine European fish, for seven distinct populations of the European seabass, Dicentrarchus labrax. The use of δ202Hg and Δ199Hg values in SIBER enabled us to estimate Hg isotopic niches, successfully discriminating several populations. Recursive-partitioning analyses demonstrated the relevance of Hg stable isotopes as discriminating tools. Hg isotopic values also provided insight on Hg contamination sources for biota in coastal environment. The overall narrow range of δ202Hg around Europe was suggested to be related to a global atmospheric contamination while δ202Hg at some sites was linked either to background contamination, or with local contamination sources. Δ199Hg was related to Hg levels of fish but we also suggest a relation with ecological conditions. Throughout this study, results from the Black Sea population stood out, displaying a Hg cycling similar to fresh water lakes. Our findings bring out the possibility to use Hg isotopes in order to discriminate distinct populations, to explore the Hg cycle on a large scale (Europe) and to distinguish sites contaminated by global versus local Hg source. The interest of using Hg sable isotopes to investigate the whole European Hg cycle is clearly highlighted.

Stable isotope composition of mercury forms in flue gases from a typical coal-fired power plant, Inner Mongolia, northern China

Mercury forms emitted from coal combustion via air pollution control devices are speculated to carry different Hg isotope signatures. Yet, their Hg isotope composition is still not reported. Here, we present the first onsite Hg isotope data for gaseous elemental Hg (GEM) and gaseous oxidized Hg (GOM) of flue gases from a typical lignite-fired power plant (CFPP). Significant mass dependent fractionation (MDF) and insignificant mass independent fractionation (MIF) are observed between feed coal and coal combustion products. As compared to feed coal (δ202Hg=−2.04±0.25‰), bottom ash, GEM and GOM in flue gases before and after wet flue gas desulfurization system significantly enrich heavy Hg isotopes by 0.7–2.6‰ in δ202Hg, while fly ash, desulfurization gypsum and waste water show slight but insignificant enrichment of light Hg isotopes. GEM is significantly enriched heavy Hg isotopes compared to GOM and Hg in fly ash. Our observations verify the previous speculation on Hg isotope fractionation mechanism in CFPPs, and suggest a kinetically-controlled mass dependent Hg isotope fractionation during transformation of Hg forms in flue gases. Finally, our data are compared to Hg isotope compositions of atmospheric Hg pools, suggesting that coal combustion Hg emission is likely an important atmospheric Hg contributor.

Variations in the isotopic composition of stable mercury isotopes in typical mangrove plants of the Jiulong estuary, SE China

Variations in the composition of stable isotopes of mercury contained in tissues (root, stem, leaf, and hypocotyl or flower) of three typical mangrove plants (Kandelia candel, Aegiceras corniculata, and Bruguiera gymnorhiza), collected from the mangrove wetland of Jiulong estuary, SE China, were used to investigate the sources and transformation of mercury in the mangrove plants. Tissue samples from the plants were digested and mercury in the solution was pre-concentrated with purge-trap method and then analyzed by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The results showed that the mass dependent fractionation (MDF) of mercury ranged from -2.67 to -0.87‰ for δ 202Hg while the mass independent fractionation (MIF) of mercury isotopes ranged from -0.16 to 0.09 and -0.19 to 0.05‰ for Δ199Hg and Δ201Hg, respectively, relative to the standard NIST SRM 3133. The ratio of Δ199Hg/Δ201Hg was 0.991, indicating that the mercury had been photo-reduced before being accumulated in mangrove plants. Analyses of the data from MIF studies revealed that the major portion of the mercury measured in leaves (∼90%) originated from the atmosphere while the source of over half of the mercury present in roots was the surficial sediment. This study, the first of its kind investigating the variations in isotopic composition of mercury in the tissues of mangrove plants, could be helpful to identify the source of mercury contamination in mangroves and understand the biogeochemical cycle of mercury in the estuarine mangrove wetlands.

Mercury isotope compositions across North American forests

AbstractForest biomass and soils represent some of the largest reservoirs of actively cycling mercury (Hg) on Earth, but many uncertainties exist regarding the source and fate of Hg in forest ecosystems. We systematically characterized stable isotope compositions of Hg in foliage, litter, and mineral soil horizons across 10 forest sites in the contiguous United States. The mass‐independent isotope signatures in all forest depth profiles are more consistent with those of atmospheric Hg(0) than those of atmospheric Hg(II), indicating that atmospheric Hg(0) is the larger source of Hg to forest ecosystems. Within litter horizons, we observed significant enrichment in Hg concentration and heavier isotopes along the depth, which we hypothesize to result from additional deposition of atmospheric Hg(0) during litter decomposition. Furthermore, Hg isotope signatures in mineral soils closely resemble those of the overlying litter horizons suggesting incorporation of Hg from litter as a key source of soil Hg. The spatial distribution of Hg isotope compositions in mineral soils across all sites is modeled by isotopic mixing assuming atmospheric Hg(II), atmospheric Hg(0), and geogenic Hg as major sources. This model shows that northern sites with higher precipitation tend to have higher atmospheric Hg(0) deposition than other sites, whereas drier sites in the western U.S. tend to have higher atmospheric Hg(II) deposition than the rest. We attribute these differences primarily to the higher litterfall Hg input at northern wetter sites due to increased plant productivity by precipitation. These results allow for a better understanding of Hg cycling across the atmosphere‐forest‐soil interface.

Historical variations of mercury stable isotope ratios in Arctic glacier firn and ice cores

AbstractThe concentration and isotopic composition of mercury (Hg) were determined in glacier core samples from Canadian Arctic ice caps dating from preindustrial to recent time (early 21st century). Mean Hg levels increased from ≤ 0.2 ng L−1 in preindustrial time to ~0.8–1.2 ng L−1 in the modern industrial era (last ~200 years). Hg accumulated on Arctic ice caps has Δ199Hg and Δ201Hg that are higher (~ −1 to 2.9‰) than previously reported for Arctic snow impacted by atmospheric Hg depletion events (mostly &lt; −1‰), suggesting that these events contribute little to Hg accumulation on ice caps. The range of δ202Hg, Δ199Hg, and Δ201Hg in glacier cores overlaps with that of Arctic Hg0(g) and of seawater in Baffin Bay and also with that of midlatitude precipitation and industrial Hg sources, including coal and Hg ores. A core from Agassiz ice cap (80.7°N) shows a ~ +1‰ shift in δ202Hg over the nineteenth to twentieth centuries that could reflect changes in the isotopic composition of the atmospheric Hg pool in the High Arctic in response to growing industrial emissions at lower latitudes. This study is the first ever to report on historical variations of Hg stable isotope ratios in Arctic ice cores. Results could help constrain future modeling efforts of the global Hg biogeochemical cycle and the atmosphere's response to changing Hg emissions, past and future.

Historical variations in the stable isotope composition of mercury in a sediment core from a riverine lake: Effects of dams, pulp and paper mill wastes, and mercury from a chlor-alkali plant

The Wabigoon River (Ontario, Canada) was affected by dams starting in 1898 and was polluted with pulp and paper mill wastes starting in 1913 and mercury from a chlor-alkali plant from 1962 to 1975. A dated sediment core from a riverine lake was analysed to investigate resultant changes in the biogeochemistry of mercury as revealed by variations in mercury isotope ratios and sediment chemistry. A total mercury maximum formed by the mercury pollution coincided with minimums in the δ-values of the 198Hg/202Hg, 199Hg/202Hg, 200Hg/202Hg, and 201Hg/202Hg ratios, and the δ-values decreased in the order δ201Hg > δ200Hg > δ199Hg > δ198Hg. Thus, mass-dependent fractionation caused depletion in lighter isotopes, implying evaporation of Hg(0) and pollution of the atmosphere as well as the river-lake system. Concurrently, mass-independent fractionation caused 199Hg enrichment, possibly reflecting an independently documented upsurge in methylmercury production, and 201Hg depletion, suggesting removal of methylmercury with anomalously high 201Hg/199Hg ratios by aquatic organisms and accumulation of 201Hg-depleted inorganic Hg(II) in sediments. The δ201Hg/δ199Hg ratio rose abruptly when mercury pollution began, reflecting the resultant increase in methylmercury production, and remained high but gradually declined as the pollution abated, paralleling trends shown by methylmercury in aquatic organisms. The δ201Hg/δ199Hg ratio of pre-1962 background mercury increased ca. 1898 and ca. 1913–1929, suggesting accelerated methylmercury production due to stimulation of microbial activities by the damming of the river and the input of pulp and paper mill wastes, respectively. Other variations were linked to economic and technological factors that affected pulp and paper manufacture.

Mercury isotope signatures of seawater discharged from a coal-fired power plant equipped with a seawater flue gas desulfurization system

Seawater flue gas desulfurization (SFGD) systems are commonly used to remove acidic SO2 from the flue gas with alkaline seawater in many coastal coal-fired power plants in China. However, large amount of mercury (Hg) originated from coal is also transferred into seawater during the desulfurization (De-SO2) process. This research investigated Hg isotopes in seawater discharged from a coastal plant equipped with a SFGD system for the first time. Suspended particles of inorganic minerals, carbon residuals and sulfides are enriched in heavy Hg isotopes during the De-SO2 process. δ202Hg of particulate mercury (PHg) gradually decreased from −0.30‰ to −1.53‰ in study sea area as the distance from the point of discharge increased. The results revealed that physical mixing of contaminated De-SO2 seawater and uncontaminated fresh seawater caused a change in isotopic composition of PHg isotopes in the discharging area; and suggested that both De-SO2 seawater and local background contributed to PHg. The impacted sea area predicted with isotopic tracing technique was much larger than that resulted from a simple comparison of pollutant concentration. It was the first attempt to apply mercury isotopic composition signatures with two-component mixing model to trace the mercury pollution and its influence in seawater. The results could be beneficial to the coal-fired plants with SFGD systems to assess and control Hg pollution in sea area.

Isotopic Composition of Inorganic Mercury and Methylmercury Downstream of a Historical Gold Mining Region.

We measured total mercury (THg) and monomethyl mercury (MMHg) concentrations and mercury (Hg) isotopic compositions in sediment and aquatic organisms from the Yuba River (California, USA) to identify Hg sources and biogeochemical transformations downstream of a historical gold mining region. Sediment THg concentrations and δ(202)Hg decreased from the upper Yuba Fan to the lower Yuba Fan and the Feather River. These results are consistent with the release of Hg during gold mining followed by downstream mixing and dilution. The Hg isotopic composition of Yuba Fan sediment (δ(202)Hg = -0.38 ± 0.17‰ and Δ(199)Hg = 0.04 ± 0.03‰; mean ± 1 SD, n = 7) provides a fingerprint of inorganic Hg (IHg) that could be methylated locally or after transport downstream. The isotopic composition of MMHg in the Yuba River food web was estimated using biota with a range of %MMHg (the percent of THg present as MMHg) and compared to IHg in sediment, algae, and the food web. The estimated δ(202)Hg of MMHg prior to photodegradation (-1.29 to -1.07‰) was lower than that of IHg and we suggest this is due to mass-dependent fractionation (MDF) of up to -0.9‰ between IHg and MMHg. This result is in contrast to net positive MDF (+0.4 to +0.8‰) previously observed in lakes, estuaries, coastal oceans, and forests. We hypothesize that this unique relationship could be due to differences in the extent or pathway of biotic MMHg degradation in stream environments.