Distribution of total and organic mercury in soils around an artisanal and small-scale gold mining area in West Java, Indonesia (original) (raw)
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Environmental Science and Pollution Research, 2016
This study investigates the distribution of total mercury (T-Hg) and methylmercury (MeHg) in the soil and water around the artisanal and small-scale gold mining (ASGM) area along the Cikaniki River, West Java, Indonesia. The concentration of T-Hg and MeHg in the forest soil ranged from 0.07 to 16.7 mg kg −1 and from <0.07 to 2.0 μg kg −1 , respectively, whereas it ranged from 0.40 to 24.9 mg kg −1 and from <0.07 to 56.3 μg kg −1 , respectively, in the paddy field soil. In the vertical variation of the T-Hg of forest soil, the highest values were observed at the soil surface, and these values were found to decrease with increasing depth. A similar variation was observed for MeHg and total organic carbon content (TOC), and a linear relationship was observed between them. Mercury deposited on the soil surface can be trapped and retained by organic matter and subjected to methylation. The slope of the line obtained for the T-Hg vs. TOC plot became larger near the ASGM villages, implying a higher rate of mercury deposition in these areas. In contrast, the plots of MeHg vs. TOC fell along the same trend line regardless of the distance from the ASGM village. Organic carbon content may be a predominant factor in controlling MeHg formation in forest soils. The T-Hg concentration in the river water ranged from 0.40 to 9.6 μg L −1. River water used for irrigation can prove to be a source of mercury for the paddy fields. The concentrations of Hg 0 and Hg 2+ in river water showed similar variations as that observed for the T-Hg concentration. The highest Hg 0 concentration of 3.2 μg L −1 can be attributed to the waste inflow from work sites. The presence of Hg 0 in river water can become a source of mercury present in the atmosphere along the river. MeHg concentration in the river water was found to be 0.004-0.14% of T-Hg concentration, which was considerably lower than the concentrations of other Hg species. However, MeHg comprised approximately 0.2% of the T-Hg in paddy field soil. Mercury deposited from the atmosphere and the river water can be subjected to methylation. Paddy fields are very important ecosystems; therefore, the effect of MeHg on these ecosystems and human beings should be further investigated.
The role of ground vegetation in the uptake of mercury and methylmercury in a forest ecosystem
2003
Litterfall from trees has been identified as an important pathway for deposition of mercury (Hg) and methylmercury (MeHg) in forested catchments, but very little is known about the role of ground vegetation in deposition and cycling of Hg compounds. This study was conducted to identify the origin of Hg compounds in the ground vegetation, and to estimate the role of its litterfall with respect to pools and fluxes of Hg in a coniferous forest in the German Fichtelgebirge mountains. Above and below ground biomass of the dominant ground vegetation (Vaccinium myrtillus, Deschampsia flexuosa and Calamagrostis villosa) were sampled at several plots successively during the growing season. The fluxes to the soil via litterfall of the ground vegetation were calculated using contents of Hg and MeHg in the annual fractions of aboveground biomass. With fluxes of 0.4-7.8 mg Hg total ha −1 a −1 and 0.01-0.04 mg MeHg ha −1 a −1 (depending on the plant species) this pathway contributes only a few percent to the total deposition of both compounds in the catchment. To identify the uptake pathways of Hg compounds, the same plant species were grown in a pot experiment with addition of isotope labelled Hg compounds (202 Hg 2+ , Me 198 Hg) to a clean sand substrate. Only small proportions of 202 Hg and Me 198 Hg in the substrate were taken up by the plants, but in all cases the proportion translocated into aboveground biomass after uptake was greater in case of Me 198 Hg. Thus, internal recycling in the plant-soil system is a source especially for MeHg in the ground vegetation. However, as compared to the input of Hg compounds by tree litterfall and storage in the forest floor, Hg total and MeHg in ground vegetation are of minor importance. High volatilization of added Hg isotopes raises the question of a re-emission of Hg compounds by the transpiration flux of the ground vegetation.
Journal of Geophysical Research: Biogeosciences, 2017
Global mercury contamination largely results from direct primary atmospheric and secondary legacy emissions, which can be deposited to ecosystems, converted to methylmercury, and bioaccumulated along food chains. We examined organic horizon soil samples collected across an elevational gradient on Whiteface Mountain in the Adirondack region of New York State, USA to determine spatial patterns in methylmercury concentrations across a forested montane landscape. We found that soil methylmercury concentrations were highest in the midelevation coniferous zone (0.39 ± 0.07 ng/g) compared to the higher elevation alpine zone (0.28 ± 0.04 ng/g) and particularly the lower elevation deciduous zone (0.17 ± 0.02 ng/g), while the percent of total mercury as methylmercury in soils decreased with elevation. We also found a seasonal pattern in soil methylmercury concentrations, with peak methylmercury values occurring in July. Given elevational patterns in temperature and bioavailable total mercury ...
Potential sources of methylmercury in tree foliage
Environmental Pollution, 2012
Litterfall is a major source of mercury (Hg) and toxic methylmercury (MeHg) to forest soils and influences exposures of wildlife in terrestrial and aquatic ecosystems. However, the origin of MeHg associated with tree foliage is largely unknown. We tested the hypothesis that leaf MeHg is influenced by root uptake and thereby related to MeHg levels in soils. Concentrations of MeHg and total Hg in deciduous and coniferous foliage were unrelated to those in soil at 30 urban and rural forested locations in southwest Ohio. In contrast, tree genera and trunk diameter were significant variables influencing Hg in leaves. The fraction of total Hg as MeHg averaged 0.4% and did not differ among tree genera. Given that uptake of atmospheric Hg 0 appears to be the dominant source of total Hg in foliage, we infer that MeHg is formed by in vivo transformation of Hg in proportion to the amount accumulated.
Water Research, 2011
► Mercury and monomethylmercury were investigated in a tropical head watershed of French Guiana. ► The pristine area covered by oxisol acted as a sink for both species from rain and throughfall inputs. ► Hg contaminated soils of the former gold-mining flat were identified as a source of methylmercury. ► Monomethylmercury was mainly produced at the beginning of the rainy season and released latter on. ► As gold-mining continues to expand, an enhancement of methylmercury bioamplification is expected.
Biogeochemical factors affecting mercury methylation rate in two contaminated floodplain soils
Biogeosciences, 2012
An automated biogeochemical microcosm system allowing controlled variation of redox potential (E H) in soil suspensions was used to assess the effect of various factors on the mobility of mercury (Hg) as well as on the methylation of Hg in two contaminated floodplain soils with different Hg concentrations (approximately 5 mg Hg kg −1 and >30 mg Hg kg −1). The experiment was conducted under stepwise variation from reducing (approximately −350 mV at pH 5) to oxidizing conditions (approximately 600 mV at pH 5). Results of phospholipid fatty acids (PLFA) analysis indicate the occurrence of sulfate reducing bacteria (SRB) such as Desulfobacter species (10Me16:0, cy17:0, 10Me18:0, cy19:0) or Desulfovibrio species (18:2ω6,9), which are considered to promote Hg methylation. The products of the methylation process are lipophilic, highly toxic methyl mercury species such as the monomethyl mercury ion [MeHg + ], which is named as MeHg here. The ln(MeHg/Hg t) ratio is assumed to reflect the net production of monomethyl mercury normalized to total dissolved Hg (Hg t) concentration. This ratio increases with rising dissolved organic carbon (DOC) to Hg t ratio (ln(DOC/Hg t) ratio) (R 2 = 0.39, p < 0.0001, n = 63) whereas the relation between ln(MeHg/Hg t) ratio and lnDOC is weaker (R 2 = 0.09; p < 0.05; n = 63). In conclusion, the DOC/Hg t ratio might be a more important factor for the Hg net methylation than DOC alone in the current study. Redox variations seem to affect the biogeochemical behavior of dissolved inorganic Hg species and MeHg indirectly through related changes in DOC, sulfur cycle, and microbial community structure whereas E H and pH values, as well as concentration of dissolved Fe 3+ /Fe 2+ and Cl − seem to play subordinate roles in Hg mobilization and methylation under our experimental conditions.
Evidence for Elevated Production of Methylmercury in Salt Marshes
Environmental Science & Technology, 2007
epth variations of total mercury (Hg) and methylmercury (MeHg) concentrations were obtained in cores from nonvegetated sediments, sediments colonized by Sarcocornia fruticosa, Halimione portulacoides, and Spartina maritima and below-ground biomass in three Portuguese estuaries. Similar analyses were also performed on the above-ground plant tissues. Concentrations in below-ground biomass exceeded up to 9 (Hg) and 44 (MeHg) times the levels in sediments. Mercury and MeHg in below-ground biomass were up to 400 (Hg) and 4700 (MeHg) times higher than those found in above-ground parts, indicating a weak upward translocation. Methylmercury in colonized sediments reached 18% of the total Hg, which was 70 times above the maximum values found in nonvegetated sediments. Concentrations of MeHg in vegetated sediments were not related to plant type but were linearly proportional to the total mercury levels. The analysis of below-ground biomass at high depth resolution (2 cm) provided evidence that Hg and MeHg were elevated. The higher enrichment factors were found where the shifting of redox conditions suggested high microbial activity. Mercury and MeHg in below-ground tissues were a function of total levels in sediments and again were not plant-specific. These results suggest that the bioremediation of mercury-contaminated sediments is likely to increase the formation of methyl- mercury.
Accumulation of mercury and methylmercury by mushrooms and earthworms from forest soils
Environmental Pollution, 2011
Accumulation of total and methyl-Hg by mushrooms and earthworms was studied in thirty-four natural forest soils strongly varying in soil physico-chemical characteristics. Tissue Hg concentrations of both receptors did hardly correlate with Hg concentrations in soil. Both total and methyl-Hg concentrations in tissues were species-specific and dependent on the ecological groups of receptor. Methyl-Hg was low accounting for less than 5 and 8% of total Hg in tissues of mushrooms and earthworms, respectively, but with four times higher concentrations in earthworms than mushrooms. Total Hg concentrations in mushrooms averaged 0.96 mg Hg kg À1 dw whereas litter decomposing mushrooms showed highest total Hg and methyl-Hg concentrations. Earthworms contained similar Hg concentrations (1.04 mg Hg kg À1 dw) whereas endogeic earthworms accumulated highest amounts of Hg and methyl-Hg.
Biogeosciences, 2016
Rice paddy plantation is the dominant agricultural land use throughout Asia. Rice paddy fields have been identified as important sites for methylmercury (MeHg) production in the terrestrial ecosystem and a primary pathway of MeHg exposure to humans in mercury (Hg) mining areas. We compared the source and distribution of Hg species in different compartments of the rice paddy during a complete rice-growing season at two different typical Hg-contaminated mining sites in Guizhou province, China: an abandoned site with a high Hg concentration in soil but a low concentration in the atmosphere and a current-day artisanal site with a low concentration in soil but a high concentration in the atmosphere. Our results showed that the flux of new Hg to the ecosystem from irrigation and atmospheric deposition was insignificant relative to the pool of old Hg in soil; the dominant source of MeHg to paddy soil is in situ methylation of inorganic Hg (IHg). Elevated MeHg concentrations and the high pr...
Water, Air, & Soil Pollution, 2000
This study compares mercury (Hg) and methylmercury (MeHg) distribution in the soils of two forested stream watersheds at Acadia National Park, Maine, U.S.A. Cadillac Brook watershed, which burned in 1947, has thin soils and predominantly deciduous vegetation. It was compared to the unburned Hadlock Brook watershed, with thicker soil and predominantly coniferous vegetation. Soils in both watersheds were primarily well drained. The fire had a significant impact on the Cadillac watershed, by raising the soil pH, altering the vegetation, and reducing carbon and Hg pools. Total Hg content was significantly higher (P < 0.05) in Hadlock soils (0.18 kg Hg ha −1 ) compared to Cadillac soils (0.13 kg Hg ha −1 ). Hadlock O horizon had an average Hg concentration of 134±48 ng Hg g −1 dry weight, compared to 103±23 ng Hg g −1 dry weight in Cadillac O horizon. Soil pH was significantly higher in all soil horizons at Cadillac compared to Hadlock soils. This difference was especially significant in the O horizon, where Cadillac soils had an average pH of 3.41±0.22 compared to Hadlock soils with an average pH of 2.99±0.13. To study the mobilization potential of Hg in the O horizons of the two watersheds, batch adsorption experiments were conducted, and the results were modeled using surface complexation modeling. The results of Hg adsorption experiments indicated that the dissolved Hg concentration was controlled by the dissolved organic carbon (DOC) concentration. The adsorption isotherms suggest that Hg is more mobile in the O horizon of the unburned Hadlock watershed because of higher solubility of organic carbon resulting in higher DOC concentrations in that watershed. Methylmercury concentrations, however, were consistently higher in the burned Cadillac O horizon (0.20±0.13 ng Hg g −1 dry weight) than in the unburned Hadlock O horizon (0.07±0.07 ng Hg g −1 dry weight). Similarly, Cadillac soils possessed a higher MeHg content (0.30 g MeHg ha −1 ) than Hadlock soils (0.16 g MeHg ha −1 ). The higher MeHg concentrations in Cadillac soils may reflect generally faster rates of microbial metabolism due to more rapid nutrient cycling and higher soil pH in the deciduous forest. In this research, we have shown that the amount of MeHg is not a function of the total pool of Hg in the watershed. Indeed, MeHg was inversely proportional to total Hg, suggesting that landscape factors such as soil pH, vegetation type, or land use history (e.g., fire) may be the determining factors for susceptibility to high Hg in biota.