Runsheng Yin

Mercury in the marine boundary layer and seawater of the South China Sea: Concentrations, sea/air flux, and implication for land outflow

Using R/V Shiyan 3 as a sampling platform, measurements of gaseous elemental mercury (GEM), surface seawater total mercury (THg), methyl mercury (MeHg), and dissolved gaseous mercury (DGM) were carried out above and in the South China Sea (SCS). Measurements were collected for 2 weeks (10 to 28 August 2007) during an oceanographic expedition, which circumnavigated the northern SCS from Guangzhou (Canton), Hainan Inland, the Philippines, and back to Guangzhou. GEM concentrations over the northern SCS ranged from 1.04 to 6.75 ng m(-3) (mean: 2.62 ng m(-3), median: 2.24 ng m(-3)). The spatial distribution of GEM was characterized by elevated concentrations near the coastal sites adjacent to mainland China and lower concentrations at stations in the open sea. Trajectory analysis revealed that high concentrations of GEM were generally related to air masses from south China and the Indochina peninsula, while lower concentrations of GEM were related to air masses from the open sea area, reflecting great Hg emissions from south China and Indochina peninsula. The mean concentrations of THg, MeHg, and DGM in surface seawater were 1.2 +/- 0.3 ng L-1, 0.12 +/- 0.05 ng L-1, and 36.5 +/- 14.9 pg L-1, respectively. In general, THg and MeHg levels in the northern SCS were higher compared to results reported from most other oceans/seas. Elevated THg levels in the study area were likely attributed to significant Hg delivery from surrounding areas of the SCS primarily via atmospheric deposition and riverine input, whereas other sources like in situ production by various biotic and abiotic processes may be important for MeHg. Average sea/air flux of Hg in the study area was estimated using a gas exchange method (4.5 +/- 3.4 ng m(-2) h(-1)). This value was comparable to those from other coastal areas and generally higher than those from open sea environments, which may be attributed to the reemission of Hg previously transported to this area.

Stable Mercury Isotope Variation in Rice Plants (Oryza sativa L.) from the Wanshan Mercury Mining District, SW China

To study the sources and transformations of Hg in the rice plant ( Oryza sativa L.), stable Hg isotope variations in different tissues (foliage, root, stem, and seed) of rice which were collected from the Wanshan mercury mine (WSMM, Guizhou province, SW China) were investigated by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). In comparison, Hg isotope compositions of paddy soil, lichen, and direct ambient air samples in WSMM were also analyzed. We observed that mass dependent fractionation (MDF) of Hg differed by up to ∼ 3.0‰ in δ(202)Hg values and that mass independent fractionation (MIF) of Hg isotopes affected the odd Hg isotopes to produce a ∼ 0.40‰ range in Δ(199)Hg (and Δ(201)Hg) values in tissues of rice plant. The 1:1 Δ(199)Hg/Δ(201)Hg ratio in tissues of rice supported the hypothesis that a fraction of Hg in tissues of rice plants has undergone a photoreduction process prior to being accumulated by rice plants. We suggest that the variation of MIF represents a mixing between soil Hg and atmospheric Hg in rice plants. The estimated fraction of atmospheric Hg (f) in tissues of rice followed the trend of f leaf > f stem > f seed > f root. Finally, we demonstrated a significant MDF of >1.0‰ in δ(202)Hg during the processes of absorption of atmospheric Hg by leaf tissues and of absorption of soil Hg by roots. Our study demonstrated that Hg isotopes may represent an important contribution both to the study of Hg transportation in plants and to the understanding of sources of Hg contamination to critical food crops.

Atmospheric mercury inputs in montane soils increase with elevation: evidence from mercury isotope signatures

The influence of topography on the biogeochemical cycle of mercury (Hg) has received relatively little attention. Here, we report the measurement of Hg species and their corresponding isotope composition in soil sampled along an elevational gradient transect on Mt. Leigong in subtropical southwestern China. The data are used to explain orography-related effects on the fate and behaviour of Hg species in montane environments. The total- and methyl-Hg concentrations in topsoil samples show a positive correlation with elevation. However, a negative elevation dependence was observed in the mass-dependent fractionation (MDF) and mass-independent fractionation (MIF) signatures of Hg isotopes. Both a MIF (Δ199Hg) binary mixing approach and the traditional inert element method indicate that the content of Hg derived from the atmosphere distinctly increases with altitude.

Effect of DBP/DEHP in vegetable planted soil on the quality of capsicum fruit.

Field experiment was conducted to investigate the di-n-butyl phthalate (DBP) and di-2-ethylhexyl phthalate (DEHP) contamination in Capsicum annum fruit grown in DBP and DEHP contaminated soil, and to evaluate the effect of DBP and DEHP on the quality of capsicum fruit. The top layer soil (0-10 cm) of plots was treated with a mixture of DBP and DEHP (1:1 w/w) and capsicum seedlings were transplanted. After 90 days, capsicum fruit, shoot and root samples were collected. DBP and DEHP concentration in various parts of the samples were determined by gas chromatography. Vitamin C and capsaicin contents in fruit were determined using 2,4-dinitrophenylhydrazine colorimetric analysis and sodium nitrite-sodium molybdate colorimetric analysis, respectively. The results showed that DBP concentration in fruit, shoot and root increased with the increase of soil-applied DBP/DEHP concentration, but DEHP was not detected in all samples. When the soil-applied DBP/DEHP concentration was 5, 10, 20, 40, 80 and 160 mg kg(-1) soil, compared with control, vitamin C and capsaicin content in capsicum fruit decreased by 1.6%, 5.9%, 10.6%/o, 18.2%, 19.2%, 22.6% and 1.6%, 2.5%, 12.9%, 20.1%, 22.2%, respectively. Pearson correlation analysis demonstrated that the decrease of vitamin C and capsaicin content was negatively correlated to the increase of DBP concentration in capsicum fruit, which suggested that DBP uptake by the plant might be mainly responsible for quality degradation of capsicum fruit.

Characterization of mercury species in brown and white rice (Oryza sativa L.) grown in water-saving paddies

In China, total Hg (HgT) and methylmercury (MeHg) were quantified in rice grain grown in three sites using water-saving rice cultivation methods, and in one Hg-contaminated site, where rice was grown under flooded conditions. Polished white rice concentrations of HgT (water-saving: 3.3±1.6 ng/g; flooded: 110±9.2 ng/g) and MeHg (water-saving 1.3±0.56 ng/g; flooded: 12±2.4 ng/g) were positively correlated with root-soil HgT and MeHg contents (HgT: r2=0.97, MeHg: r2=0.87, p<0.05 for both), which suggested a portion of Hg species in rice grain was derived from the soil, and translocation of Hg species from soil to rice grain was independent of irrigation practices and Hg levels, although other factors may be important. Concentrations of HgT and other trace elements were significantly higher in unmilled brown rice (p<0.05), while MeHg content was similar (p>0.20), indicating MeHg infiltrated the endosperm (i.e., white rice) more efficiently than inorganic Hg(II).

Mercury Stable Isotopic Compositions in Coals from Major Coal Producing Fields in China and Their Geochemical and Environmental Implications

Total mercury (Hg) concentrations (THg) and stable mercury isotopic compositions were measured in coal samples (n = 61) from major coal producing fields in China. The THg concentrations in coals ranged from 0.05 to 0.78 μg g(-1), with a geometric mean of 0.22 μg g(-1). Hg isotopic compositions in coals showed large variations both in mass-dependent fractionation (MDF, δ(202)Hg: -2.36 to -0.14‰) and mass-independent fractionation (MIF, Δ(199)Hg: -0.44 to +0.38‰). The MIF signatures in coals may reveal important information on the coal-forming conditions (e.g., humic and sapropelic). The Δ(199)Hg/Δ(201)Hg of ∼1 determined in coals indicated that a portion of Hg has been subjected to photoreduction process prior to being incorporated to coals. On the basis of THg, Hg isotopic signatures, and other geological factors (e.g., total ash content and total sulfur content), the potential sources of Hg in coals from different coal producing regions were estimated. The main source of Hg in coals from southwestern China and eastern part of northern China is likely geogenic Hg, whereas the source of Hg in coals from other parts of northern China is mainly biogenic Hg. Finally, we estimated that Hg emission from coal combustion in China is characterized by diagnostic Hg isotopic signatures (δ(202)Hg: ∼-0.70‰ and Δ(199)Hg: ∼-0.05‰). The present study demonstrates that Hg isotopes can serve as a tool in understanding the sources and transformation of Hg in coals and may also be used as a tracer to quantify Hg emissions from coal combustion.

Identifying the sources and processes of mercury in subtropical estuarine and ocean sediments using Hg isotopic composition.

The concentrations and isotopic compositions of mercury (Hg) in surface sediments of the Pearl River Estuary (PRE) and the South China Sea (SCS) were analyzed. The data revealed significant differences between the total Hg (THg) in fine-grained sediments collected from the PRE (8-251 μg kg(-1)) and those collected from the SCS (12-83 μg kg(-1)). Large spatial variations in Hg isotopic compositions were observed in the SCS (δ(202)Hg, from -2.82 to -2.10‰; Δ(199)Hg, from +0.21 to +0.45‰) and PRE (δ(202)Hg, from -2.80 to -0.68‰; Δ(199)Hg, from -0.15 to +0.16‰). The large positive Δ(199)Hg in the SCS indicated that a fraction of Hg has undergone Hg(2+) photoreduction processes prior to incorporation into the sediments. The relatively negative Δ(199)Hg values in the PRE indicated that photoreduction of Hg is not the primary route for the removal of Hg from the water column. The riverine input of fine particles played an important role in transporting Hg to the PRE sediments. In the deep ocean bed of the SCS, source-related signatures of Hg isotopes may have been altered by natural geochemical processes (e.g., Hg(2+) photoreduction and preferential adsorption processes). Using Hg isotope compositions, we estimate that river deliveries of Hg from industrial and urban sources and natural soils could be the main inputs of Hg to the PRE. However, the use of Hg isotopes as tracers in source attribution could be limited because of the isotope fractionation by natural processes in the SCS.

Isotopic Composition of Atmospheric Mercury in China: New Evidence for Sources and Transformation Processes in Air and in Vegetation

The isotopic composition of atmospheric total gaseous mercury (TGM) and particle-bound mercury (PBM) and mercury (Hg) in litterfall samples have been determined at urban/industrialized and rural sites distributed over mainland China for identifying Hg sources and transformation processes. TGM and PBM near anthropogenic emission sources display negative δ(202)Hg and near-zero Δ(199)Hg in contrast to relatively positive δ(202)Hg and negative Δ(199)Hg observed in remote regions, suggesting that different sources and atmospheric processes force the mass-dependent fractionation (MDF) and mass-independent fractionation (MIF) in the air samples. Both MDF and MIF occur during the uptake of atmospheric Hg by plants, resulting in negative δ(202)Hg and Δ(199)Hg observed in litter-bound Hg. The linear regression resulting from the scatter plot relating the δ(202)Hg to Δ(199)Hg data in the TGM samples indicates distinct anthropogenic or natural influences at the three study sites. A similar trend was also observed for Hg accumulated in broadleaved deciduous forest foliage grown in areas influenced by anthropogenic emissions. The relatively negative MIF in litter-bound Hg compared to TGM is likely a result of the photochemical reactions of Hg(2+) in foliage. This study demonstrates the diagnostic stable Hg isotopic composition characteristics for separating atmospheric Hg of different source origins in China and provides the isotopic fractionation clues for the study of Hg bioaccumulation.

Mercury distribution in the soil–plant–air system at the Wanshan mercury mining district in Guizhou, Southwest China

The level of mercury bioaccumulation in wild plants; the distribution of bioavailable Hg, elemental Hg, and total Hg in soil; and the concentration of total gaseous Hg (TGM) in ambient air was studied at three different mining sites (SiKeng [SK], WuKeng [WK], and GouXi [GX]) in the Wanshan mercury mining district of China. Results of the present study showed that the distribution of soil total Hg, elemental Hg, bioavailable Hg, and TGM varies across the three mining sites. Higher soil total Hg (29.4-1,972.3 mg/kg) and elemental Hg (19.03-443.8 mg/kg) concentrations were recorded for plots SK and WK than for plot GX. Bioavailable Hg was lower at plot SK and GX (SK, 3-12 ng/g; GX, 9-14 ng/g) than at plot WK (11-1,063 ng/g), although the TGM concentration in the ambient air was significantly higher for plot GX (52,723 ng/m(3) ) relative to WK (106 ng/m(3) ) and SK (43 ng/m(3)). Mercury in sampled herbage was elevated and ranged from 0.8 to 4.75 mg/kg (SK), from 2.17 to 34.38 mg/kg (WK), and from 47.45 to 136.5 mg/kg (GX). Many of the sampled plants are used as fodder or for medicinal purposes. High shoot Hg concentrations may therefore pose an unacceptable human health risk. Statistical analysis of the recorded data showed that the Hg concentration in plant shoots was positively correlated with TGM and that the Hg concentration in roots was positively correlated with the bioavailable Hg concentration in the soil. The bioaccumulation factor (BAF) in the present study was defined with reference to the concentration of bioavailable Hg in the soil (Hg([root]) /Hg([bioavail])). Three plant species, Macleaya cordata L., Achillea millefolium L., and Pteris vittata L., showed enhanced accumulation of Hg and therefore may have potential for use in the phytoremediation of soils of the Wanshan mining area.

Mercury Isotopes as Proxies to Identify Sources and Environmental Impacts of Mercury in Sphalerites

During the past few years, evidence of mass independent fractionation (MIF) for mercury (Hg) isotopes have been reported in the Earth’s surface reservoirs, mainly assumed to be formed during photochemical processes. However, the magnitude of Hg-MIF in interior pools of the crust is largely unknown. Here, we reported significant variation in Hg-MIF signature (Δ199Hg: −0.24 ~ + 0.18‰) in sphalerites collected from 102 zinc (Zn) deposits in China, indicating that Hg-MIF can be recorded into the Earth’s crust during geological recycling of crustal material. Changing magnitudes of Hg-MIF signals were observed in Zn deposits with different formations, evidence that Hg isotopes (especially Hg-MIF) can be a useful tracer to identify sources (syngenetic and epigenetic) of Hg in mineral deposits. The average isotopic composition in studied sphalerites (δ202Hgaverage: −0.58‰; Δ199Hgaverage: +0.03‰) may be used to fingerprint Zn smelting activities, one of the largest global Hg emission sources.