Mercury In Soils Research Articles

Pollution Characteristics and Risk Assessments of Mercury in Jiutai, a County Region Thriving on Coal Mining in Northeastern China

Among human activities, coal mining and the combustion of fossil fuels are important sources of mercury in the environment. Research on mercury pollution in coal mining areas and surrounding cities, especially in densely populated areas, has always been at the forefront of this research field. In order to study the characteristics of environmental mercury pollution in small and medium-sized coal mining areas and surrounding towns in China, this study selected the main urban area of Jiutai District, a typical mining town in the Changchun City circle industrial base in northeast China, as the research object. In this study, the geo-accumulation index (Igeo) was used to study the soil mercury pollution degree in Jiutai District, the potential ecological risk index (Er) was used to evaluate the potential ecological risk of soil mercury in the study area, and the human exposure risk assessment model was used to evaluate the non-carcinogenic risk of soil mercury to the human body. The results showed that 32% of the soil samples in the study area had a higher mercury content than the regional soil background value of Jilin Province (0.04 mg·kg−1). According to the Igeo, 19% of the sample sites in the study area were polluted (index > 0). In general, the soil mercury pollution level in Jiutai District is low, and the polluted areas are mainly concentrated in the northeast of the study area. The Er of the soil mercury in the study area ranged from 7.2 to 522.0, with 32% of the sampling sites having a moderate or above potential ecological risk (Er > 40), and the potential ecological risk level of the soil mercury was higher in the northeast of the study area. The non-carcinogenic risk index (HQ) and total non-carcinogenic risk value (HI) of the soil mercury were all far less than 1, indicating that soil mercury pollution in the study area did not harm the health of local adults. The oral ingestion of soil mercury is the main form of human exposure to mercury.

Perceptions and realities of mercury contamination in a Peruvian artisanal and small-scale gold mining (ASGM) community

Artisanal and small-scale gold mining (ASGM) is the leading global source of mercury pollution. Efforts to reduce or eliminate mercury use in ASGM have produced limited results, in part because they do not engage the complex socio-technical nature of mercury issues in ASGM. The paper takes a multidisciplinary approach to understand the mercury issue with a socio-technical lens, pairing sampling of mercury in soils with surveys of miners' and residents' perceptions of mercury pollution and its dispersion. The research was conducted in Secocha, an ASGM boomtown in southern Peru. Mercury levels in soils exceeded relevant standards in both industrial zones (average of 72.6 mg/kg, versus the Peruvian standard of 24 mg/kg) and residential/urban zones (average of 9.5 mg/kg, versus the Peruvian standard of 6.6 mg/kg). Mercury levels were highest where processing and gold buying activity were concentrated. Surveys revealed that miners and residents correctly assumed mercury pollution to be highest in those areas. However, respondents seemed to underestimate the extent of mercury pollution in other parts of town, and many believed that only those who handle mercury directly were affected by it. Respondents also placed low priority on reducing mercury pollution. Miners' and residents’ partial knowledge about mercury contamination and the low priority accorded to the issue suggest that mercury reduction efforts would likely be met with indifference and potentially resistance.

Ecological Safety and Spatial Distribution of Mercury and Arsenic in Qinghai Spruce Ecosystems in Remote Plateau Mountains, Northwest China

The long-distance transport of toxic elements is a crucial external source of metals accumulated in remote forest ecosystems. Due to the harsh environmental conditions and the complexity and diversity of influencing factors in remote alpine ecosystems, research on toxic elements is very limited, especially in the dry zone. In this regard, mercury (Hg) and arsenic (As) in soil and plant samples were investigated in a Qinghai spruce forest ecosystem at Sidalong Forest Farm (SDL), in the Qilian Mountains, northwest China. The results of the study showed a significant variation in the spatial distribution of Hg and As in soils, but a highly similar spatial distribution trend was found in mosses. High Hg and As concentrations in plants were found in moss, bark, and litterfall; the concentration of Hg was particularly high (BCF > 1). The Qilian Mountain spruce forest ecosystem was contaminated with exogenous Hg and As, with Hg, in particular, being the most serious form of contamination. The study results can provide baseline data for future forest management and research in the spruce forest ecosystem in Qinghai, northwest China.

Distribution of Mercury in Soil, Water, and Vegetable Fern in a Former Gold Mining Area – Evidence from Nagan Raya Regency, Aceh Province, Indonesia

Distribution of Mercury in Soil, Water, and Vegetable Fern in a Former Gold Mining Area – Evidence from Nagan Raya Regency, Aceh Province, Indonesia

Mercury fractionation, bioavailability, and the major factors predicting its transfer and accumulation in soil–wheat systems

Soil mercury (Hg) and its bioaccumulation in food crops have attracted widespread concerns globally due to its harmful effects on biota. However, soil mercury fractionation, bioavailability, and the major factors predicting its transfer and accumulation in soil–wheat-systems have not been thoroughly explored. Twenty-one (21) soil samples collected throughout China with a wide spectrum of physico-chemical characteristics were contaminated with HgCl2 and winter wheat (Triticum aestivum L.) was grown on the soils in a greenhouse pot-culture experiment for 180 days. A four-step sequential extraction was used segregating soil Hg into water-soluble (F1, 0.21 %), exchangeable (F2, 0.07 %), organically bound (F3, 16.40 %), and residual fractions (F4, 83.32 %). Step-wise multiple linear regression (SMLR) and path analysis (PA) were used to develop a prediction model and identify the major controlling factors of soil-wheat Hg transference. The SMLR results revealed that wheat Hg in leaves, husk, and grain was positively correlated with soil total and available Hg, and crystalline manganese (Cryst-Mn), while negatively correlated with soil pH, amorphous manganese (Amor-Mn) and crystalline aluminium (Cryst-Al). Bioconcentration factor (BCF) values were significantly higher in acidic soils (highest 0.05), with phytotoxic effects in some soils, as compared to alkaline soils (lowest 0.006). Furthermore, wheat grain Hg was significantly correlated with total (R2 = 0.25), water-soluble (R2 = 0.54) and NH4Ac-extractable Hg (R2 = 0.43) while also had a good correlation with soil pH (R2 = −0.20). In conclusion, the soil total and available Hg (water-soluble + exchangeable fraction), pH, organic matter, and Amor-Mn are the most important soil variables that support Hg uptake in the wheat plants, which benefit managing Hg-enriched agricultural soils for safe wheat production.

Incorporating soil mercury species and fractions into multi-objective risk assessment of a residue disposal site in China.

Environmental problems in soil and water caused by solid waste dumps have become a growing concern. This study proposes an integrated risk assessment model aimed at multi-objectives including human, ecology and groundwater and develops remediation target values at different tiers associated with soil mercury species and fractions in a typical residue disposal site of China. The results show that the residue disposal site was severely contaminated with mercury, with the maximum mercury content in the soil reaching 579.14mg/kg. The average concentration of vapour mercury, bioaccessible mercury, bioavailable mercury and leachable mercury tested in laboratory was 87.65mg/kg, 3.15mg/kg (intestinal phase), 1.654mg/kg and 0.045mg/L, respectively. The hazard index calculated using total mercury, bioaccessible mercury and vapour mercury was 7.43 E + 01, 4.42 E + 01, and the remediation target values were7.79mg/kg and 13.1mg/kg, respectively. The ecological risk for total mercury and bioavailable mercury was calculated using measured site soil mercury background values of 6390.92 and 94.52, and the remediation target was 0.7mg/kg and 47.33mg/kg, respectively. Under Class IV water conditions, the measured and three-phase equilibrium model simulations of leachable mercury resulted in remediation targets of 6mg/kg and 10mg/kg for soil mercury. Compared to total mercury, the remediation target values calculated using mercury species and fractions were significantly larger under human health protection, ecology protection and groundwater protection. This results in a reduction in the area of soil to be remediated by 20.3-85.7%, resulting in significant savings in remediation costs. It was concluded that when conducting risk assessment and reuse of mercury-contaminated sites, it is important to consider the species and fractions of mercury in the soil in order to reasonably determine the remediation criteria and scale of remediation to avoid over-remediation and incomplete remediation. At the same time, a comprehensive protection target remediation mechanism should be established by combining different receptors.

Syntrichia caninervis adapt to mercury stress by altering submicrostructure and physiological properties in the Gurbantünggüt Desert

Sewage and industrial waste discharges have been found to have a deleterious effect on plant growth and environmental safety through the accumulation of trace metal mercury (Hg) in soils. Although the effects of Hg on vascular plants have been reported in terms of enzyme activity, oxidative damage and physiology, few studies have been done on non-vascular plants. A simulation experiment including 7 Hg concentrations (0, 10, 20, 30, 40, 50, 75 µM) was conducted to investigate the influence of Hg stress on ultrastructure and physiological properties of biocrust moss Syntrichia. caninervis across 7 consecutive days. The results showed that the lowest lethal concentration of S. caninervis was 30 µM Hg. The mortality rate of the plants increased significantly with Hg concentrations. The ultrastructure did not change significantly at Hg concentration ≤ 20 µM, while exceeding which, cell walls began to separate, nuclei began to blur, and chloroplasts began to expand. The soluble sugars (SS), peroxidase (POD), and superoxide dismutase (SOD) activities increased initially and then decreased with the increase of concentration in the time gradient, with the largest values at 20 µM. The contents of malondialdehyde (MDA) and proline (Pro) increased with the increase of Hg concentration, both reached peak value at 50 µM. However, chlorophyll (Chl) contents continued to decrease along both the concentration and time gradients. Pearson correlation and principal component analysis showed that two principal components (PC1 and PC2) explained 73.9% of the variance in plant adaptation to Hg stress. SOD, POD, Chl, SS, and Pro all responded well to Hg in S. caninervis. Our study showed that Hg stress caused changes in ultrastructure and physiological metabolism of S. caninervis. 20 µM was the maximum concentration of Hg that biocrust moss S. caninervis can tolerate. S. caninervis mainly adopted two adaptation strategies related to exclusion and accumulation to reduce Hg stress.

Evaluation of Mercury Pollution in Soil of Different Land Use Types in Coal-fired Industrial Area

The geo-accumulation index, potential ecological risk index, health risk model, and geographical detector were used to evaluate the soil mercury (Hg) concentrations and assess the health risks for various land use types to reveal the characteristics and spatial variability of soil Hg pollution under different land uses in the coal-fired industrial area of the Loess Plateau. The study area included seven counties in the western part of Xinzhou City, Shanxi province. The results showed that the average ω(Hg) in the agricultural land, grass land, wood land, and residential land were 0.48, 0.34, 0.58, and 0.52 mg·kg-1, respectively, which were 16.00, 11.33, 19.33, and 17.33 times higher than the background value, respectively. The variation coefficients were ranked as residential land>agricultural land>grass land>wood land. The evaluation results of the geo-accumulation index and potential ecological risk index indicated a high ecological risk of Hg pollution in the entire study area with extreme pollution points in certain aeras. The health risk assessment results indicated no non-carcinogenic health risks for children and adults in the study area from Hg. Additionally, the geographical detection results revealed that the spatial variability in Hg was mainly impacted by industrial and agricultural activities in agricultural land, by soil organic matter and pH value in grass land, by soil salinity in wood land, and by soil salinity and organic matter in residential land. The spatial distribution pattern of Hg concentrations peaked in both the northern and southern edges, with a decreasing trend towards the middle and the majorly polluted areas being caused by human activities such as coal mining and industrial production.

Sources, Microbial Interaction and Available Strategies for Remediation of Heavy Metals

High concentrations of heavy metals (Cadmium, Arsenic, Chromium, Lead, Mercury, Copper, Cobalt, Zinc, Nickel, and Selenium) in soil are threat to the ecosystem, human health, food safety, animal health. Heavy metal contaminants are increasing rapidly due to industrialization especially automobile industry. Previously, various techniques were developed and improved over time like encapsulation, surface capping, landfilling, soil washing, soil flushing, electro kinetic extraction, solidification, stabilization, phytoremediation, and bioremediation. These techniques minimize the contaminants by utilizing immobilization, containment and removal mechanisms. Bioremediation is a promising technique that utilizes the capability of plants and microbial resources for decontamination of ecosystem from heavy metal contaminants. Microbes have shown capability to utilize heavy metal remediation and assist plant tolerance for heavy metal accumulation. Earlier published studies have not yet completely evaluated proficiencies to large scale however, in the present review, critical analysis of reported techniques focusing on the bioremediation have been discussed. In depth analysis for the heavy metal remediation is of paramount importance of heavy metal contaminant emerging issue of soil pollution.

Bioavailability and health risk of toxic heavy metals (As, Hg, Pb and Cd) in urban soils: A Monte Carlo simulation approach

Toxic heavy metals pollution in urban soil has become a major global issue due to its adverse effects on the environment and human health. In this paper, 26 soil samples were analyzed to assess the speciation, bioavailability and human health risk of Arsenic (As), Mercury (Hg), Lead (Pb) and Cadmium (Cd) in urban soils of a heavy industrial city in NE China by using a Monte Carlo simulation approach. The results showed that As, Hg, Pb and Cd concentrations in the soil all exceed the corresponding background value of study area. Mercury displays the highest value of geo-accumulation index (Igeo), followed by Cd, Pb and As. The pollution load index (PLI) value (>2) indicates a moderate pollution level in the study area. The chemical speciation of HMs mainly exists in residual fraction except Cd. The probabilistic health risk assessment demonstrated that the mean values of Total Carcinogenic Risk (TCR) and Hazard Index (HI) calculated with total concentration are at the unacceptable level, with a higher risk to children than adults. However, the mean values calculated with bioavailable fraction are all within the acceptable level. The mean value of TCR and HI obtained by bioavailable fraction is about 96% and 95% lower than that obtained by total concentration, respectively. Thus, this study suggested that the bioavailable fraction of HMs is a more reliable parameter for health risk assessment, while the total concentration of HMs can overestimate the true risk. The results of this study provide some insight into the speciation, bioavailability and health risks of toxic heavy metals in urban soils in those heavy industrial cities.

Mercury in soils of the conterminous United States: patterns and pools

Soils account for the largest global mercury reservoirs, but observations are sparse in many regions. The accumulation and turnover of mercury in soils determines whether they act as an atmospheric source or sink. Here, we present a spatial analysis of soil mercury from a large soil survey (three horizons, ∼4800 sites) across the conterminous United States conducted by the U.S. Geological Survey. Soil mercury pools were calculated for 11 layers, cumulatively representing the top 1 m of soil, and totaling 158 ± 2 Gg (±SD) of mercury (20.3 ± 0.2 mg m−2). Mercury areal density was greatest in mixed forest (27.3 ± 0.5 mg m−2), cropland (25.3 ± 0.3 mg m−2), and deciduous forest (25.6 ± 0.5 mg m−2) ecosystems and lowest in barren (13.5 ± 0.3 mg m−2) and shrubland (12.6 ± 0.2 mg m−2) ecosystems. Assessment of the provenance of soil mercury using bedrock titanium normalization suggests that 62%–95% of soil mercury is unexplained by parental sources.

Modelling mercury concentration in Ghanaian soil

Mercury usage in Artisanal Small Scale Gold Mining is a major anthropogenic source of mercury in the environment. In this study, mercury pools and fluxes have been established for Ghana, which has a large ASGM sector, based on estimated losses of mercury to the environment, deposition calculated with GLEMOS, a global long-range transport model for mercury in air, and mercury measured in soils and water in Ghana. A model for mercury in soils and water of Ghana with a resolution of 5 × 5 km2 and a monthly or yearly time step has been developed to assess the regional increase in soil and water concentrations that can be attributed to anthropogenic sources and to simulate scenarios into the future. The model has been calibrated to reproduce present-day mercury concentration in the soil (average 0.0193 mg kg−1) with current deposition calculated with the long-range transport model and past years’ deposition based on a scenario for the historic development of the mining activity. This calculation gives an average increase in soil concentrations from anthropogenic sources of 22%. The model gives a fair description of the regional differences in soil concentrations but underestimates concentrations in regions with intense mining activity and overestimates concentrations in regions with less mining when using deposition from the long-range model as input.

Mercury in the Environment Around Industrially Impacted Locations in India: A Mini-Review.

India is a major emitter of mercury to the environment. This mini-review condenses the information available since 2008 on mercury in air, soil, sediment, biota and human biomarkers near industrial locations. Information from eight regions was analyzed. More than 40% of studies did not report sufficient QA/QC information on analysis methods. Highest quality was observed for studies on human biomarkers, biota, and sediments, and the lowest on water quality. Concentrations of mercury in sediments (up to 3650µg/kg), human biomarkers (up to 31µg/g) and fish (up to 3µg/g) in the vicinity of coal-fired power plants and iron and steel were high in general, and sometimes comparable to or higher than the global guideline, screening or reference values. Overall, impacts of industrial activities on mercury pollution of surrounding environment were evident, and warrant a speedy assessment of other industrial areas and implementation of mitigation measures.

Monitoring soil mercury content based on hyperspectral data and machine learning methods

Mercury (Hg) is a heavy metal pollutant characterized by global migration, high bioaccumulation, and high biological toxicity. Soil Hg pollution seriously harms soil environmental quality and human health. The higher the content of Hg in the soil, the more serious the harm. Therefore, the acquisition of soil Hg content information is crucial for soil monitoring and restoration, and human health. The purpose of this study is to establish the best hyperspectral prediction model of soil Hg content in the study area. A total of 90 soil samples were collected from the mining areas and suburbs, and the Hg content was analyzed. Several preprocessing methods were applied to the hyperspectral data. Partial least-squares regression (PLSR), orthogonalized PLSR, random forest, and back propagation neural network (BPNN) were used to establish the relationship between soil hyperspectral data and soil Hg content to predict the soil Hg content. Specifically, the transferability of the best prediction model in yellow-brown and cinnamon soil data was discussed. The results showed that BPNN + standard normal variable + full-band (4 nm) is the optimum method to predict soil Hg content (Rtrain2=0.94, Rtest2=0.85). The transferability of the model is the best in yellow-brown soil. This research provides technical support for the rapid monitoring of soil Hg pollution information in central and eastern Shaanxi-Province, and the results enrich prediction models of soil Hg content in different soil types.

Mercury in soils of intermountain depressions in the Western Baikal region

The article presents original data on the gross concentration of Hg in soils of various types in the territory of the southwestern Baikal region. Quantitative estimates of Hg distribution over the area of intermountain depressions and slopes of mountain ranges have been obtained. The features of the distribution of Hg concentrations in the surface component of soils depending on the type of soils, granulometric composition, hydrolytic acidity, the sum of exchangeable bases, the degree of saturation with bases, pH, humus, CO, N, and humic acids were revealed. The forms of Hg occurrence in soils of different types are determined: the largest proportion of Hg is in the forms associated with organic complexes and exchangeable bases. The calculated indicators indicate an increased natural geochemical background of mercury in soils, which is associated with the territorial belonging to the Baikal rift zone.

Source Apportionment of Speciated Mercury in Chinese Rice Grain Using a High-Resolution Model.

Rice grain consumption is a primary pathway of human mercury exposure. To trace the source of rice grain mercury in China, we developed a rice paddy mercury transport and transformation model with a grid resolution of 1 km × 1 km by using the unit cell mass conservation method. The simulated total mercury (THg) and methylmercury (MeHg) concentrations in Chinese rice grain ranged from 0.08 to 243.6 and 0.03 to 238.6 μg/kg, respectively, in 2017. Approximately, 81.3% of the national average rice grain THg concentration was due to atmospheric mercury deposition. However, soil heterogeneity, especially the variation in soil mercury, led to the wide rice grain THg distribution across grids. Approximately, 64.8% of the national average rice grain MeHg concentration was due to soil mercury. In situ methylation was the main pathway via which the rice grain MeHg concentration was increased. The coupled impact of high mercury input and methylation potential led to extremely high rice grain MeHg in partial grids among Guizhou province and junctions with surrounding provinces. The spatial variation in soil organic matter significantly impacted the methylation potential among grids, especially in Northeast China. Based on the high-resolution rice grain THg concentration, we identified 0.72% of grids as heavily polluted THg grids (rice grain THg > 20 μg/kg). These grids mainly corresponded to areas in which the human activities of nonferrous metal smelting, cement clinker production, and mercury and other metal mining were conducted. Thus, we recommended measures that are targeted at the control of heavy pollution of rice grain by THg according to the pollution sources. In addition, we observed a wide spatial variation range of MeHg to THg ratios not only in China but also in other regions of the world, which highlights the potential risk of rice intake.

English

Heavy metals exist in the environment naturally aside those due to anthropogenic impact. These metals are removed from effluents and water using different techniques like adsorption, oxidation/reduction, chemical precipitation, membrane separation, filtration and ion exchange. Biosorption is very effective because it is highly renewed naturally, is cheap, and can remove metals greatly because the pollutant can be recovered either by desorbing or incinerating the biomass. Therefore, this work aims to identify some biochars utilized as adsorbents to remove lead, chromium, mercury and copper in soil and water, according to different researchers. In conclusion adsorption is a very effective method to remove or recover heavy metals from the environment. These biochars can be used in place of commercial activated charcoal because, besides being cheap, they are very effective treatment in removing metal ions based on wastewater discharge standards.   Key words: Biomass, adsorbents, activated carbon, biochar, heavy metals.

Detection of heavy metals in vegetable soil based on THz spectroscopy

Heavy metal pollution in soil endangers food safety and human health. Thus, it is important to study accurate and rapid detection methods. Here, an efficient nondestructive detection method for mercury (Hg), cadmium (Cd) and copper (Cu) in soils was studied by terahertz (THz) spectroscopy. First, regression equations were established between heavy metal contents and absorption coefficients at the selected frequency points. Then, the pollution type and pollution level of the soils containing three heavy metals were detected at the same time. Reference blank soil was also tested. Probabilistic neural network (PNN) and random forest (RF) models verified the effects of qualitative detection. Next, the contents of the three heavy metals in soils were predicted simultaneously by a backpropagation neural network (BPNN) and an extreme learning machine (ELM). The results showed that the absorption coefficients increased regularly in the THz spectral range from 0.05 THz to 0.7 THz. The average detection result of the PNN model was better than that of RF. The average detection accuracy for heavy metal pollution level and type were all higher than 95%. In addition, the prediction results of heavy metal content showed that BPNN model has better prediction performance. The optimal decision coefficients (DC) of BPNN model for soils containing three heavy metals were 0.95, 0.99 and 0.98, respectively, and their corresponding root mean square errors (RMSE) were 0.37, 0.02 and 2.62, respectively. The results proved that THz spectroscopy has good qualitative and quantitative detection ability for soils contaminated with Hg, Cd and Cu, which could bring new opportunities for detection of heavy metal pollutants in soil.

The Legacy of Mercury Contamination from a Past Leather Manufacturer and Health Risk Assessment in an Urban Area (Pisa Municipality, Italy)

An abandoned open green space in the urban setting of the Municipality of Pisa (Tuscany, Italy) has been designed for renewal to foster the development of recreational activities and improve the lives of the surrounding communities. However, the geochemical site characterization revealed Pb, Cu, Zn and Hg concentrations in the soil exceeding the thresholds imposed by Italian regulations for residential use. Pb, Cu and Zn contents likely reflect the effects of urban vehicle traffic, while Hg contamination represents the legacy of a past artisanal tannery that used Hg(II)-chloride in leather processing in the mid-1900s. Mercury is widely distributed in the area, with the highest concentration in the uppermost soil layer, and reaching about 170 mg/kg in the common dandelion rhizosphere. Chemical extractions and thermal desorption experiments have indicated that most Hg is in the elemental free and matrix-bound fraction, with a possible minor amount (less than 4 wt%) of HgS and negligible methylated forms (0.1 wt%). The data suggest that soil processes could reduce Hg2+ to volatile Hg0. Mercury in groundwater, hosted in a shallow aquitard in the area, was below 0.2 µg/L. However, the presence of chloride in groundwater might result in the formation of Hg stable aqueous complexes, increasing Hg release from solids. Future water quality monitoring is hence recommended. The risk assessment highlighted that mercury in soil carries a risk of non-cancerous effects, in particular for children, posing the basis for management planning.

Quantifying diffuse contamination: Comparing silver and mercury in organogenic and minerogenic soil

For both, silver (Ag) and mercury (Hg), the median concentrations in an aqua regia extraction of minerogenic top- and subsoil from continental scale geochemical surveys (Australia, China, Europe) are around 0.02 mg/kg. When the soil O horizon is collected as topsoil sample, the concentration of again both elements is higher by about a factor of 10 (range 7–30), with median concentrations around 0.2 mg/kg Ag and Hg. Geochemical maps of top- and subsoil at different scales for both elements display regional patterns which reflect mainly geology, climate and topography. Anthropogenic sources like mines, power plants, or major cities visually occur only as local anomalies. For Ag in organogenic topsoil the maximum possible input due to diffuse contamination is estimated to be in the 0.02 mg/kg range, about 10% of the median concentration in the soil O horizon. For Hg this value is slightly higher at 0.03 mg/kg. In the soil O horizon Hg concentrations show less variability than in the C horizon. Substantial Hg soil contamination should lead to noticeably increased Hg/Ag ratios.