Xuewu Fu

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.

Methylmercury Accumulation in Rice (Oryza sativa L.) Grown at Abandoned Mercury Mines in Guizhou, China

Mercury is a global pollutant that can transform into methylmercury, a highly toxic and bioaccumulative organic form. Previous surveys have shown that fish is the main source of human methylmercury exposure, whereas most other food products have an average value below 20 microg/kg and primarily in the inorganic form. This paper reports that methylmercury in rice (Oryza sativa L.) grown at abandoned mercury mining areas contained levels >100 microg/kg in its edible portion and proved to be 10-100 times higher than other crop plants. The daily adult intake of methylmercury through rice consumption causes abnormally high methylmercury exposure to humans. The results demonstrate that rice is a methylmercury bioaccumulative plant and the main methylmercury source for human exposure in the areas studied.

A review of studies on atmospheric mercury in China

Due to the fast developing economy, mercury (Hg) emissions to the atmosphere from Chinese mainland have increased rapidly in recent years. Consequently, this issue has received a considerable attention internationally. This paper reviews the current understanding of and knowledge on atmospheric Hg emissions, distribution and transport in China. The magnitude of Hg emissions to the atmosphere from Chinese anthropogenic sources has been estimated to be in the range of 500-700 tons per year, whereby comprising a significant proportion of the globe total anthropogenic emissions. Emissions of Hg from natural surfaces including bare soil, water, and vegetation covered soil tend in a comparison to be higher in China than in Europe and North America, indicating the importance of this source category. Atmospheric Hg exhibits a significant concentration variability among urban, semi-remote, and remote areas. Total Gaseous Mercury (TGM) concentrations in urban areas of China were often 1.5 - 5 folds higher compared to the corresponding settings in North America and Europe. In turn, particulate mercury (PHg) concentrations in urban areas of China were up to two orders of magnitude higher compared to North America and Europe. Atmospheric observations made at strictly remote sites in China also include the presence of occasional high concentrations of TGM, and the more short-lived fractions PHg and Reactive Gaseous Mercury (RGM). Accordingly, Hg deposition fluxes tended to be higher in China, with remote areas and urban areas being 1-2 times and 1-2 magnitude higher than those in North America and Europe, respectively.

Elevated atmospheric deposition and dynamics of mercury in a remote upland forest of southwestern China

Mt. Gongga area in southwest China was impacted by Hg emissions from industrial activities and coal combustion, and annual means of atmospheric TGM and PHg concentrations at a regional background station were 3.98 ng m(-3) and 30.7 pg m(-3), respectively. This work presents a mass balance study of Hg in an upland forest in this area. Atmospheric deposition was highly elevated in the study area, with the annual mean THg deposition flux of 92.5 microg m(-2) yr(-1). Total deposition was dominated by dry deposition (71.8%), and wet deposition accounted for the remaining 28.2%. Forest was a large pool of atmospheric Hg, and nearly 76% of the atmospheric input was stored in forest soil. Volatilization and stream outflow were identified as the two major pathways for THg losses from the forest, which yielded mean output fluxes of 14.0 and 8.6 microg m(-2) yr(-1), respectively.

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.

Atmospheric Mercury Transfer to Peat Bogs Dominated by Gaseous Elemental Mercury Dry Deposition

Gaseous elemental mercury (GEM) is the dominant form of mercury in the atmosphere. Its conversion into oxidized gaseous and particulate forms is thought to drive atmospheric mercury wet deposition to terrestrial and aquatic ecosystems, where it can be subsequently transformed into toxic methylmercury. The contribution of mercury dry deposition is however largely unconstrained. Here we examine mercury mass balance and mercury stable isotope composition in a peat bog ecosystem. We find that isotope signatures of living sphagnum moss (Δ(199)Hg = -0.11 ± 0.09‰, Δ(200)Hg = 0.03 ± 0.02‰, 1σ) and recently accumulated peat (Δ(199)Hg = -0.22 ± 0.06‰, Δ(200)Hg = 0.00 ± 0.04‰, 1σ) are characteristic of GEM (Δ(199)Hg = -0.17 ± 0.07‰, Δ(200)Hg = -0.05 ± 0.02‰, 1σ), and differs from wet deposition (Δ(199)Hg = 0.73 ± 0.15‰, Δ(200)Hg = 0.21 ± 0.04‰, 1σ). Sphagnum covered during three years by transparent and opaque surfaces, which eliminate wet deposition, continue to accumulate Hg. Sphagnum Hg isotope signatures indicate accumulation to take place by GEM dry deposition, and indicate little photochemical re-emission. We estimate that atmospheric mercury deposition to the peat bog surface is dominated by GEM dry deposition (79%) rather than wet deposition (21%). Consequently, peat deposits are potential records of past atmospheric GEM concentrations and isotopic composition.

Mercury distribution and speciation in water and fish from abandoned Hg mines in Wanshan, Guizhou province, China

Concentrations of total mercury (Hg(T)), methylmercury (MeHg), and its speciation in water samples as well as fish collected from abandoned Hg mines in Wanshan, Guizhou province, China, were measured to show regional dispersion of Hg contaminations that are not well known. High Hg(T) and MeHg(T) (total methylmercury) concentrations obtained in waters from mining areas, ranged from 15 to 9300 ng/l and 0.31 to 25 ng/l, respectively. MeHg(T) were not correlated with Hg(T), whereas, peak values in both cases were in accord with high concentrations of particulate fraction, which appeared to be enhanced during high-flow regime with ratios reaching to 99%. Elevated Hg concentrations in the particulate form indicated that particles released from Hg mining tailings (calcines) might be an important pathway of Hg to the aquatic system. The concentrations of total Hg in fish muscle were elevated ranging from 0.061 to 0.68 mg/kg, but MeHg were generally low ranging from 0.024 to 0.098 mg/kg with a mean ratio of 28%. The concentrations and distribution patterns of Hg in aquatic systems suggested derivation from historic Hg mining sites in the Wanshan area.

Temporal and spatial distributions of total gaseous mercury concentrations in ambient air in a mountainous area in southwestern China: Implications for industrial and domestic mercury emissions in remote areas in China

Spatial and temporal distributions of total gaseous mercury (TGM) concentrations in ambient air were investigated in the Mt. Gongga area (Sichuan province, PR China) from April 2006 to June 2007. The annual geometric mean TGM concentration at the Moxi baseline station was 3.90+/-1.20 ng m(-3). Geometric mean TGM concentrations at 14 representative sampling sites during the warm season ranged from 1.60 to 20.1 ng m(-3) and varied spatially, with levels decreasing between urbanized areas and more remote regions: urban area (U1-U3: 7.76+/-4.57 to 20.1+/-15.1 ng m(-3)), town (T1: 4.61+/-1.15 ng m(-3)) and village (V1-V4: 3.26+/-0.63 to 8.45+/-3.06 ng m(-3)), and remote area (R1-R6: 1.60+/-0.43 to 3.41+/-1.26 ng m(-3)). Our study suggested that industrial activities, especially non-ferrous smelting activities, were an important source of atmospheric Hg and played a vital role in the regional distribution of TGM. In addition, domestic coal and biomass combustion to heat residential homes were important sources of TGM in densely populated areas during the winter months.

Atmospheric mercury concentrations observed at ground-based monitoring sites globally distributed in the framework of the GMOS network

Long-term monitoring of data of ambient mercury (Hg) on a global scale to assess its emission, transport, atmospheric chemistry, and deposition processes is vital to understanding the impact of Hg pollution on the environment. The Global Mercury Observation System (GMOS) project was funded by the European Commission (http://www.gmos.eu) and started in November 2010 with the overall goal to develop a coordinated global observing system to monitor Hg on a global scale, including a large network of ground-based monitoring stations, ad hoc periodic oceanographic cruises and measurement flights in the lower and upper troposphere as well as in the lower stratosphere. To date, more than 40 ground-based monitoring sites constitute the global network covering many regions where little to no observational data were available before GMOS. This work presents atmospheric Hg concentrations recorded worldwide in the framework of the GMOS project (2010-2015), analyzing Hg measurement results in terms of temporal trends, seasonality and comparability within the network. Major findings highlighted in this paper include a clear gradient of Hg concentrations between the Northern and Southern hemispheres, confirming that the gradient observed is mostly driven by local and regional sources, which can be anthropogenic, natural or a combination of both.

Exchange fluxes of Hg between surfaces and atmosphere in the eastern flank of Mount Gongga, Sichuan province, southwestern China

In situ total gaseous mercury (TGM) concentrations and mercury exchange fluxes from 17 sampling sites of three representative landscapes (agriculture, grassland, and forest) were intensively measured in the eastern flank of Mount Gongga area, Sichuan province, southwestern China, from October 2005 to September 2006. Average TGM concentrations in ambient air ranged from 1.60 to 5.10 ng m(-3) in warm season, while the values were highly elevated in cold season with the highest mean TGM concentration of 7.65 ng m(-3). Hg fluxes from agriculture and grassland sampling sites showed clearly seasonal distribution pattern with net depositions observed in cold season and net emissions observed in warm season. Mean Hg fluxes at agriculture and grassland field fell in the range from -4.1 to 132.0 ng m(-2) h(-1) and from -18.7 to 13.4 ng m(-2) h(-1), respectively, while mean Hg fluxes from forest sites varied from 0.5 to 9.3 ng m(-2) h(-1). Notable diurnal pattern of Hg fluxes were observed from all sampling sites, with the maximum Hg fluxes observed at midday and the minimum values observed during the nighttime. TGM concentrations in cold season significantly negatively correlated with Hg flux, suggesting that highly elevated TGM concentration could inhibit Hg emission even cause significant deposition. Vegetation acted as a great sink of air Hg in cold season, while in warm season, it could significantly inhibit Hg emission from surfaces.