Soil Mercury Concentrations Research Articles

Citric acid facilitated thermal treatment: An innovative method for the remediation of mercury contaminated soil

Thermal treatment is a promising technology for the remediation of mercury contaminated soils, but it often requires high energy input at heating temperatures above 600°C, and the treated soil is not suitable for agricultural reuse. The present study developed a novel method for the thermal treatment of mercury contaminated soils with the facilitation of citric acid (CA). A CA/Hg molar ratio of 15 was adopted as the optimum dosage. The mercury concentration in soils was successfully reduced from 134mg/kg to 1.1mg/kg when treated at 400°C for 60min and the treated soil retained most of its original soil physiochemical properties. During the treatment process, CA was found to provide an acidic environment which enhanced the volatilization of mercury. This method is expected to reduce energy input by 35% comparing to the traditional thermal treatment method, and lead to agricultural soil reuse, thus providing a greener and more sustainable remediation method for treating mercury contaminated soil in future engineering applications.

Deforestation and cultivation mobilize mercury from topsoil

Terrestrial biomass and soils are a primary global reservoir of mercury (Hg) derived from natural and anthropogenic sources; however, relatively little is known about the fate and stability of Hg in the surface soil reservoir and its susceptibility to change as a result of deforestation and cultivation. In southwest Ohio, we measured Hg concentrations in soils of deciduous old- and new-growth forests, as well as fallow grassland and agricultural soils that had once been forested to examine how, over decadal to century time scales, man-made deforestation and cultivation influence Hg mobility from temperate surface soils. Mercury concentrations in surficial soils were significantly greater in the old-growth than new-growth forest, and both forest soils had greater Hg concentrations than cultivated and fallow fields. Differences in Hg:lead ratios between old-growth forest and agricultural topsoils suggest that about half of the Hg lost from deforested and cultivated Ohio soils may have been volatilized and the other half eroded. The estimated mobilization potential of Hg as a result of deforestation was 4.1mgm−2, which was proportional to mobilization potentials measured at multiple locations in the Amazon relative to concentrations in forested surface soils. Based on this relationship and an estimate of the global average of Hg concentrations in forested soils, we approximate that about 550Mmol of Hg has been mobilized globally from soil as a result of deforestation during the past two centuries. This estimate is comparable to, if not greater than, the amount of anthropogenic Hg hypothesized by others to have been sequestered by the soil reservoir since Industrialization. Our results suggest that deforestation and soil cultivation are significant anthropogenic processes that exacerbate Hg mobilization from soil and its cycling in the environment.

Accumulation and oxidation of elemental mercury in tropical soils

The role of chemical and mineralogical soil properties in the retention and oxidation of atmospheric mercury in tropical soils is discussed based on thermal desorption analysis. The retention of gaseous mercury by tropical soils varied greatly both quantitatively and qualitatively with soil type. The average natural mercury content of soils was 0.08±0.06μgg−1 with a maximum of 0.215±0.009μgg−1. After gaseous Hg0 incubation experiments, mercury content of investigated soils ranged from 0.6±0.2 to 735±23μgg−1, with a mean value of 44±146μgg−1. Comparatively, A horizon of almost all soil types adsorbed more mercury than B horizon from the same soil, which demonstrates the key role of organic matter in mercury adsorption. In addition to organic matter, pH and CEC also appear to be important soil characteristics for the adsorption of mercury. All thermograms showed Hg2+ peaks, which were predominant in most of them, indicating that elemental mercury oxidized in tropical soils. After four months of incubation, the thermograms showed oxidation levels from 70% to 100%. As none of the samples presented only the Hg0 peak, and the soils retained varying amounts of mercury despite exposure under the same incubation conditions, it became clear that oxidation occurred on soil surface. Organic matter seemed to play a key role in mercury oxidation through complexation/stabilization of the oxidized forms. The lower percentages of available mercury (extracted with KNO3) in A horizons when compared to B horizons support this idea.

The bioaccessibility of soil-based mercury as determined by physiological based extraction tests and human biomonitoring in children

Environmental contaminants associated with soil particles are generally less bioavailable than contaminants associated with other exposure media where chemicals are often found in more soluble forms. In vitro methods, such as Physiological Based Extraction Tests (PBET), can provide estimates of bioaccessibility for soil-based contaminants. The results of these tests can be used to predict exposure to contaminants from soil ingestion pathways within human health risk assessment (HHRA). In the current investigation, an HHRA was conducted to examine the risks associated with elevated concentrations of mercury in soils in the northern Canadian smelter community of Flin Flon, Manitoba. A PBET was completed for residential soils and indicated mean bioaccessibilities of 1.2% and 3.0% for total mercury using gastric phase and gastric+intestinal phase methodologies, respectively. However, as many regulators only allow for the consideration of in vitro results for lead and arsenic in the HHRA process, in vitro bioaccessibility results for mercury were not utilized in the current HHRA. Based on the need to assume 100% bioaccessibility for inorganic mercury in soil, results from the HHRA indicated the need for further assessment of exposure and risk. A biomonitoring study was undertaken for children between 2 and 15years of age in the community to examine urinary inorganic mercury concentrations. Overall, 375 children provided valid urine samples for analysis. Approximately 50% of urine samples had concentrations of urinary inorganic mercury below the limit of detection (0.1μg/L), with an average creatinine adjusted concentration of 0.11μg/g. Despite high variability in mercury soil concentrations within sub-communities, soil concentrations did not appear to influence urinary mercury concentrations. The results of the current investigation indicate that mercury bioaccessibility in residential soils in the Flin Flon area was likely limited and that HHRA estimates would have been better approximated through inclusion of the in vitro study results.

Concentration and distribution of mercury in drainage catchment sediment and alluvial soil of China

The China Geochemical Baselines (CGB) project provides nation-wide catchment sediment/alluvial soil geochemical baseline data for 76 elements including Hg from 3382 top (0–25cm) and 3380 deep sediment/alluvial soil samples (under a depth of 100cm) at 3382 sampling sites, corresponding to a sampling density of about 1 site per 3000km2. Mercury was determined by cold vapour generation atomic fluorescence spectrometry (AFS) under strict quality control using field duplicates, standard reference materials and analytical replicate samples. The 25th percentile is at 13 and 11μg/kg in top and deep sediment/alluvial soil samples, respectively; these concentrations are close to the crustal abundance in China. The median Hg value is at 26 and 18μg/kg in top and deep sediment/alluvial soil samples, respectively; the 75th percentile is 56μg/kg in top and 36μg/kg in deep sediment/alluvial soil samples. Mercury concentrations at the 50th (26μgHg/kg) and 75th (56μgHg/kg) percentiles exhibit systematic enrichment in the near-surface material. The Hg distribution maps show distinct increasing trends from northern to southern and from western to eastern China, which are primarily related to the distribution of parent rocks, including rocks associated with mineral resources of Hg, Sb, Au, As, Pb–Zn, and climate, resulting in different soil types, as well as to population density with accompanying industrial development. Anomalous Hg concentrations in top sediment/alluvial soil samples above the 85th percentile (87μg/kg) occur mainly in south and south-west and sparsely in north and east China; they most likely have a dual origin, natural and human-induced, with the latter having a greater contribution because of the intense industrial activities, and particularly mercury emissions from Hg, Sb, As, Au, Pb–Zn mining, coal combustion, and production of batteries, fluorescent lamps, thermometers and cement. The spatial distribution map of Hg ratios of top to deep sediment/alluvial soil samples displays higher values, suggesting that top samples are most likely polluted from human activities in the highly populated urban areas of eastern China. About 6.86% and 3.52% of top and deep sediment/alluvial soil samples, respectively, have Hg concentrations higher than the soil contamination limit of 150μg/kg set by the National Environmental Standards for Heavy Metals of the People's Republic of China.

大伙房水库土壤汞动态与污染特征研究

为了解大伙房水库汞污染现状和环境风险，选择10个采样点，采集了30个土壤样品，20个水体样品，30个空气样品，分析不同区域土壤、水体和大气中的总汞含量及分布，并采用地累积指数法和潜在生态风险指数法对比探讨了土壤总汞污染现状和环境风险，分析其生物可利用性及其潜在风险，探究大气汞与土壤汞富集的关系。结果表明，大伙房水库土壤中的汞平均含量分别为27.76 μg/kg，变异系数为69.32，最大值为82.47 μg/kg，最小值为12.49 μg/kg；大伙房水库采集水中的汞平均含量分别为19.87 μg/kg，变异系数为71.35，最大值为53.82 μg/kg，最小值为2.92 μg/kg。向大气释放汞的年排放通量17.80~62.47 μg/m2/h，平均37.76 μg/m2/h。土壤汞含量与大气汞浓度的相关系数为0.81** (P < 0.01)，相关显著，土壤汞富集对大气汞污染的贡献较大。从汞的空间分布表明，社河流域汞金属污染较低，浑河苏子河流域沉积物汞金属含量较高，水中汞含量较低。地累积指数的土壤汞污染评价和潜在生态危害指数的土壤汞生态风险评价，两种评价结果表明大伙房水库污染水平和生态风险都较低，大气汞污染对土壤汞富集的贡献较大。 To explore the pollution situation and the environmental risk of mercury in Dahuofang reservoir, we choose 10 sampling points, collected 30 soil samples, 20 water samples and 30 air samples to analyze the contents and distribution of mercury in soil, water and air in different areas. We discuss the pollution status and environmental risks of mercury in soil, analyze the biological availability and potential risks and explore the relationship between the atmospheric mercury and the soil mercury enrichment by the geoaccumulation index method and potential ecological risk index method. The results indicated that the average content of mercury in the soil of Dahuofang reser-voir were 27.76 μg/kg, the variation coefficient was 69.32, The maximum was 82.47 μg/kg, the minimum was 12.49 μg/kg; The average content of mercury in the collected water of Dahuofang reservoir were 19.87 μg/kg, The variation coefficient was 71.35, the maximum was 53.82 μg/kg, the minimum was 2.92 μg/kg. The released mercury flux into the atmosphere was 17.80 - 62.47 μg/m2/h, the average was 37.76 μg/m2/h. The correlation coefficient between mercury content in soil and the mercury concentration in atmospheric was 0.81** (P < 0.01), they were significantly correlated. The soil mercury enrichment contributed greatly to atmospheric mercury pollution. According to the spatial distribution of mercury, it indicated that the river was slightly polluted. The mercury content in sediment of Hun River and Suzi River was higher, and the content of mer-cury in water was lower. The evaluation of soil mercury pollution by geoaccumulation index method and the soil mercury ecological risk assessment by potential ecological risk index method. The results showed that the pollution level and the ecological risk of Dahuofang reservoir were low, atmospheric mercury pollution contributed great to soil mercury enrichment.

Influence of soil mercury concentration and fraction on bioaccumulation process of inorganic mercury and methylmercury in rice (Oryza sativa L.).

Recent studies showed that rice is the major pathway for methylmercury (MeHg) exposure to inhabitants in mercury (Hg) mining areas in China. There is, therefore, a concern regarding accumulation of Hg in rice grown in soils with high Hg concentrations. A soil pot experimental study was conducted to investigate the effects of Hg-contaminated soil on the growth of rice and uptake and speciation of Hg in the rice. Our results imply that the growth of rice promotes residual fraction of Hg transforming to organic-bound fraction in soil and increased the potential risks of MeHg production. Bioaccumulation factors deceased for IHg but relatively stabilized for MeHg with soil total mercury (THg) increasing. IHg in soil was the major source of Hg in the root and stalk, but leaf was contributed by Hg from both atmosphere and soil. Soluble and exchangeable Hg fraction can predict the bioavailability of IHg and MeHg in soils, and that can provide quantitative description of the rate of uptake of the bioavailable Hg. Soluble and exchangeable Hg fraction in paddy soil exceeding 0.0087 mg kg(-1) may cause THg concentration in rice grain above the permissible limit standard, and MeHg concentration in paddy soil more than 0.0091 mg kg(-1) may have the health risks to humans.

Spatial distribution of mercury in the surface soils of the urban areas, Arak, Iran.

This study assessed the baseline concentrations and spatial distribution of total mercury (Hg) in urban soils of the city of Arak, Iran. Concentrations of Hg were determined in soil collected from urban areas, and the spatial distribution was analyzed using the semivariogram approach in geostatistical technology. Mercury in soil ranged from 66.3 to 581µg/kg. The experimental variogram of soil mercury concentrations was best-fitted by a spherical model. A spatial distribution map revealed that Hg concentration showed decreasing trends from south to north, west to east and center to suburb. Overall, the results showed that Hg concentrations in urban soils of Arak may be considered medium or low.

Modelling and mapping spatio-temporal trends of heavy metal accumulation in moss and natural surface soil monitored 1990–2010 throughout Norway by multivariate generalized linear models and geostatistics

Objective. This study explores the statistical relations between the accumulation of heavy metals in moss and natural surface soil and potential influencing factors such as atmospheric deposition by use of multivariate regression-kriging and generalized linear models. Based on data collected in 1995, 2000, 2005 and 2010 throughout Norway the statistical correlation of a set of potential predictors (elevation, precipitation, density of different land uses, population density, physical properties of soil) with concentrations of cadmium (Cd), mercury and lead in moss and natural surface soil (response variables), respectively, were evaluated. Spatio-temporal trends were estimated by applying generalized linear models and geostatistics on spatial data covering Norway. The resulting maps were used to investigate to what extent the HM concentrations in moss and natural surface soil are correlated. Results. From a set of ten potential predictor variables the modelled atmospheric deposition showed the highest correlation with heavy metals concentrations in moss and natural surface soil. Density of various land uses in a 5 km radius reveal significant correlations with lead and cadmium concentration in moss and mercury concentration in natural surface soil. Elevation also appeared as a relevant factor for accumulation of lead and mercury in moss and cadmium in natural surface soil respectively. Precipitation was found to be a significant factor for cadmium in moss and mercury in natural surface soil. The integrated use of multivariate generalized linear models and kriging interpolation enabled creating heavy metals maps at a high level of spatial resolution. The spatial patterns of cadmium and lead concentrations in moss and natural surface soil in 1995 and 2005 are similar. The heavy metals concentrations in moss and natural surface soil are correlated significantly with high coefficients for lead, medium for cadmium and moderate for mercury. From 1995 up to 2010 the modelled moss and natural surface soil estimates indicate a decrease of lead concentration in both moss and natural surface soil. In the case of the moss data the decrease of accumulation is more pronounced. By contrast, the modelled cadmium and mercury concentrations do not exhibit any significant temporal trend. Conclusions. In Europe, there is hardly any nation-wide investigation of statistical correlations between the accumulation of heavy metals in moss and natural surface soil and potential influencing factors such as atmospheric deposition. This study could show that assessments of heavy metal concentrations in natural surface soil could complement biomonitoring with moss but should not replace it since the heavy metal concentrations in mosses reliably traces the spatial pattern of respective atmospheric deposition. Generalized linear models extend established methods for estimating spatial patterns and temporal trends of HM concentration in moss and natural surface soil.

Mercury removal from contaminated soil by thermal treatment with FeCl3 at reduced temperature

Thermal treatment has been used to remediate mercury-contaminated soils; however, existing thermal technologies use high temperatures (e.g., 600–800°C) and require high energy costs. Moreover, the treated soil is unfavorable for agricultural reuse. To address these issues, the present study developed a method for the thermal treatment of mercury-contaminated soils at a reduced temperature (400°C) by adding FeCl3. A FeCl3/Hg molar ratio of 100:1 in the soil was adopted as the optimum dosage of FeCl3 required to achieve maximum reduction of mercury. The mercury concentration in soils was successfully reduced to 0.8mgkg−1 when treated at 400°C for 60min and the treated soil retained most of its original soil properties. FeCl3 addition during thermal treatment not only accelerated the volatilization of mercury in the easily removed fraction but also reduced the volatilization temperature of mercury in the hardly removed fraction. The adsorbable organic halogens and PCDD/Fs formed during thermal treatment with FeCl3 would not affect the soil reuse in agriculture. The thermal decontamination method reduces energy costs and leads to agricultural soil reuse, thus providing a greener and more sustainable remediation method for treating mercury-contaminated soil in future engineering applications.

Effect of cropping systems on heavy metal distribution and mercury fractionation in the Wanshan mining district, China: implications for environmental management.

The authors studied the concentration of heavy metals and mercury fractionation in contaminated soil in 2 agricultural land use systems (paddy rice and dry land) at the Wanshan mercury mine in China. The average concentrations of chromium, lead, copper, nickel, and zinc were generally lower in paddy rice soil relative to corn field soil. Soil under corn field production was slightly contaminated with lead (22-100 mg/kg), copper (31-64 mg/kg), and nickel (22-76 mg/kg) and moderately contaminated with zinc (112-635 mg/kg). In both soils, correlation of these metals with the titanium concentration in the soil indicates a geogenic origin for each metal (lead, r = 0.48; copper, r = 0.63; nickel, r = 0.47; zinc, r = 0.48). The mercury and antimony concentration in soil was high under both cropping systems, and future remediation efforts should consider the potential environmental risk presented by these metals. The concentration of bioavailable mercury in soil ranged from 0.3 ng/g to 11 ng/g across the 2 cropping systems. The majority of mercury (>80%) was associated with organic matter and the residual fraction. However, soil under paddy rice production exhibited a significantly lower concentration of Fe/Mn oxide-bound mercury than that under corn field production. This may be a function of the reduction of Fe/Mn oxides in the paddy rice soil, with the subsequent release of adsorbed metals to the soil solution. Sequential change from corn field to paddy rice production, as practiced in Wanshan, should therefore be avoided. Mercury adsorbed to Fe/Mn oxides in corn field soil potentially could be released into the soil solution and be made available for biomethylation under the flooded water management conditions of a rice paddy.

Mercury concentrations in forest soils and stream waters in northeast and south China

Atmospheric deposition of mercury (Hg) is generally higher in China than in North America and Europe. Transport and methylation of Hg deposited in forest ecosystems may cause health risks to humans. We collected water samples from 117 small streams, and soil samples from 25 sites in forested areas in northeast and south China during 2011–2013 to investigate the spatial distribution of Hg. Results showed that Hg concentration in surface soil (0–5cm in depth) was generally higher in south China (97.8±36.0μg/kg) than that in the northeast (44.0±14.1μg/kg). In contrast, the Hg concentration in stream water was higher in northeast China (17.2±11.0ng/L) than that in the south (6.2±6.4ng/L). Hg concentrations in surface soil were positively correlated with Hg concentrations in the overlying litter Oe/Oa horizon (r2=0.84). Hg concentrations in stream water were positively correlated to DOC (dissolved organic carbon) concentrations (r2=0.43) and to the Hg concentration in the litter Oe/Oa horizon (r2=0.69). Because the litter Oe/Oa horizon represents Hg accumulated by foliage, the positive correlations indicate that atmospheric Hg deposition was an important factor affecting Hg concentrations in soils and stream water.

Bayesian importance parameter modeling of misaligned predictors: soil metal measures related to residential history and intellectual disability in children.

In this paper, we propose a novel spatial importance parameter hierarchical logistic regression modeling approach that includes measurement error from misalignment. We apply this model to study the relationship between the estimated concentration of soil metals at the residence of mothers and the development of intellectual disability (ID) in their children. The data consist of monthly computerized claims data about the prenatal experience of pregnant women living in nine areas within South Carolina and insured by Medicaid during January 1, 1996 and December 31, 2001 and the outcome of ID in their children during early childhood. We excluded mother-child pairs if the mother moved to an unknown location during pregnancy. We identified an association of the ID outcome with arsenic (As) and mercury (Hg) concentration in soil during pregnancy, controlling for infant sex, maternal race, mother's age, and gestational weeks at delivery. There is some indication that Hg has a slightly higher importance in the third and fourth months of pregnancy, while As has a more uniform effect over all the months with a suggestion of a slight increase in risk in later months.

Mercury Emission from Artisanal Buladu Gold Mine and its Bioaccumulation in Rice Grains, Gorontalo Province, Indonesia

Available forms of mercury (Hg) released from artisanal gold mine activities could be taken up increasingly by plants via root and leaf stomata. Total mercury (THg) concentrations in dry deposit, surface soil and rice grains were investigated as well as the potential risks in september 2011 from three rice fields of concern. The results revealed that the concentrations of THg in dry deposition, top soil (0 to 5 cm depth), sub soil (6 to 10 cm depth) and rice grains (Oriza sativa L.) both brown (once milled) and white (twice milled) grains were ranged from 166 to 322 m-2 day-1, 484 to 4244 μg kg-1dw, 122 to 1812 μg kg-1ww, and 113 to 1084 μg kg-1ww, respectively. Hazard quotient (HQ) values for dry deposition, top soil and sub soil were ranged from 3 to 7, 5 to 42 and 5 to 36, respectively. Target hazard quotient (THQ) for brown and white rice grains consumptions were found in the range of 0.1 to 1.6 and 0.1 to 1.0, respectively. THQ values through brown rice consumption exceeded the guideline (&gt;1) presented that the brown rice in these areas should not be safe for consumption and are at risks for the whole lifespan. However, the THQ values of both brown and white rice grains in some areas were still low and should be safe for the whole life span consumption.

Are different soil metals near the homes of pregnant women associated with mild and severe intellectual disability in children?

We explored the association of relatively low concentrations of metals in the soil proximal to maternal residence during pregnancy, with intellectual disability. We hypothesized different metals would be associated with mild versus severe intellectual disability. We used a mixed methods design, starting with a retrospective cohort from 1996 to 2002, of 10,051 pregnant mothers, soil sampling in the areas where these mothers resided during pregnancy, and follow-up of their children to determine if there was an intellectual disability outcome. We tested the soil and then predicted the soil concentration at the maternal homes, and modeled the association with the severity of the child's intellectual disability. We found a significant positive association between mild intellectual disability and soil mercury (p=0.007). For severe intellectual disability, there was a significant positive association with the soil arsenic and lead (p=0.025). This is the first report of the differential impact of metals in soil and severity of intellectual disability in children. Soil mercury concentration in the area the mother lived during pregnancy is associated with significantly increased odds of mild intellectual disability; a combination of arsenic and lead is associated with significantly increased odds of severe intellectual disability. These associations are present when controlling for maternal, child, and neighborhood characteristics.

Predicting the Concentration of Total Mercury in Mineral Horizons of Forest Soils Varying in Organic Matter and Mineral Fine Fraction Content

The level of mercury (Hg) concentration in soils can be estimated using certain predictors such as the content of organic carbon (Corg) or the fine fractions (FFs) such as silt and clay. This study was focused on the potential use of Corg and FF contents as the predictors of Hg concentration at the spatial meso-scale in forest soils derived from Triassic sandstones and claystones, Quaternary sands derived from weathering sandstones and Quaternary sands of fluvioglacial origin. To understand the importance of Corg and FF contents for Hg retention in mineral soil, the allocation of Hg in physically separated fractions of soil samples was also tested. The experiment was designed over a regular 200 × 200-m grid, where 275 plots were established. The results implied that the concentration of total Hg in mineral soil may vary by several orders of magnitude because of the natural variation in Corg content. The model where the Corg content was the only variable explained 44 % of Hg concentration variability in soil, and other significantly correlated variables were the FF content and the C/N ratio. Detailed analysis revealed that the particulate organic matter fraction accumulated more Hg per unit of Corg than in the organic matter associated with FF. The content of Corg, FF and C/N ratio allowed, for the local soils, a satisfactory prediction of the spatial distribution and the magnitude of total Hg concentration in soils.

Sources of mercury in groundwater and soils of west Gijón (Asturias, NW Spain)

This work aimed to determine the cause of the presence of high concentrations of mercury in several springs that exhibit a low concentration of metals in the bedrocks of their recharge areas in Gijón, NW Spain and the extent of this contamination. On the basis of geological mapping, different lithological substrata were analysed at the regional scale with the objective of establishing the base level of mercury in natural soils. The mercury content was simultaneously analysed in several water samples, and the following parameters were also determined: major anions and cations, As, Pb, δ34S, and δ18OSO4. The soils of the recharge area of the springs exhibited Hg concentrations that were higher than the base level established for sandstone at the regional level, and four of the total number of springs analysed exhibited Hg concentrations higher than 1μg/l. In addition, the sulphate concentration exceeded the values that this type of aquifer shows in other parts of the region. A comparison between the regionally geochemical background of soils and mercury concentration in springs and soils of the study area did not exhibit a direct relationship, suggesting an anthropogenic and timely origin (most likely from industrial emissions) for this metal. The δ34S and δ18OSO4 values of dissolved sulphate from the springs with a higher Hg concentration also indicate an anthropogenic origin.

Parameterizing Soil Emission and Atmospheric Oxidation-Reduction in a Model of the Global Biogeochemical Cycle of Mercury

Using the GEOS-Chem atmosphere-land-ocean coupled mercury model, we studied the significances of two processes, soil emission and atmospheric oxidation-reduction, in the global biogeochemical cycling of mercury and their parametrization to improve model performance. Implementing an empirical equation for soil emission flux (Esoil) including soil mercury concentration, solar radiation, and surface air temperature as parameters enabled the model to reproduce the observed seasonal variations of Esoil, whereas the default setting, which uses only the former two parameters, failed. The modified setting of Esoil also increased the model-simulated atmospheric concentration in the summertime surface layer of the lower- and midlatitudes and improved the model reproducibility for the observations in Japan and U.S. in the same period. Implementing oxidation of atmospheric gaseous elemental mercury (Hg(0)) by ozone with an updated rate constant, as well as the oxidation by bromine atoms (Br) in the default setting, improved the model reproducibility for the dry deposition fluxes observed in Japan. This setting, however, failed to reproduce the observed seasonal variations of atmospheric concentrations in the Arctic sites due to the imbalance between oxidation and reduction, whereas the model with Br as the sole Hg(0) oxidant in the polar atmosphere could capture the variations.

Spatial and vertical distribution of mercury in upland forest soils across the northeastern United States

Assessing current Hg pools in forest soils of the northeastern U.S. is important for monitoring changes in Hg cycling. The forest floor, upper and lower mineral horizons were sampled at 17 long-term upland forest sites across the northeastern U.S. in 2011. Forest floor Hg concentration was similar across the study region (274 ± 13 μg kg−1) while Hg amount at northern sites (39 ± 6 g ha−1) was significantly greater than at western sites (11 ± 4 g ha−1). Forest floor Hg was correlated with soil organic matter, soil pH, latitude and mean annual precipitation and these variables explained approximately 70% of the variability when multiple regressed. Mercury concentration and amount in the lower mineral soil was correlated with Fe, soil organic matter and latitude, corresponding with Bs horizons of Spodosols (Podzols). Our analysis shows the importance of regional and soil properties on Hg accumulation in forest soils.

The distribution of mercury around the small-scale gold mining area along the Cikaniki river, Bogor, Indonesia

The distribution of mercury in the soil, sediment and river water around the artisanal small-scale gold mining (ASGM) area along the Cikaniki River, West Java, Indonesia, was investigated. The total mercury concentration (T-Hg) in the forest soil ranged from 0.11 to 7.0mgkg−1, and the highest value was observed at the ASGM village. In the vertical T-Hg profile around the villages, the highest value was observed at the soil surface, and the concentration decreased with depth. This result suggested that the mercury released by mining activity was dispersed through the atmosphere and deposited on the surface. The total organic carbon content (TOC) showed a similar vertical profile as the T-Hg, and a linear relationship was found between T-Hg and TOC. Mercury deposited on the surface can be absorbed by organic matter. The slope of the line was larger near the ASGM village, implying a higher rate of deposition of mercury. The T-Hg in the sediment ranged from 10 to 70mgkg−1, decreasing gradually toward the lower reaches of the river. Mining waste can be transported with the river flow and deposited along the river. The distribution of the mining waste can be determined using the mineralogical composition measured by X-ray fluorescence spectrometry.