Abandoned Hg Mine Research Articles

Application of a Novel Amendment for the Remediation of Mercury Mine Sites with Hydrologic Controls

MercLokTM P-640 (MercLok) is a proprietary product developed by Albemarle as a mercury (Hg) treatment technology. MercLok captures mercury and sequesters it for a long period under ambient environmental conditions. For this project, MercLok was applied to Hg-contaminated calcines at two abandoned Hg mine sites in northern California to evaluate its efficacy in rendering such contaminated materials less hazardous and thereby reducing remediation project costs. The first application (Site 1) consisted of two calcines amended with MercLok in isolated reactor buckets under two hydrologic remediation approaches (“repository cap” and “reactive barrier”) while exposed to ambient environmental conditions. Non-amended and amended calcines and their leachates were analyzed for Hg content and related conditions during a five-month study period, demonstrating >95% reduction in leachable Hg. The second application (Site 2) involved full-scale site remediation with the application of both approaches and additional hydrologic controls to minimize run-on, erosion, and runoff. Confirmation sampling and subsequent observations indicate that the amendments and hydrologic controls effectively stabilized the site and minimized Hg releases. These application projects demonstrate the efficacy of MercLok as a component of hydrologic controls for treating Hg-contaminated material to achieve long-term mine site remediation objectives.

Ecological and health risks from heavy metal sources surrounding an abandoned mercury mine in the island paradise of Palawan, Philippines

A recent survey that determined heavy metal concentrations in an abandoned Hg mine in Palawan, Philippines, found the occurrence of Hg with As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sb, Tl, V, and Zn. While the Hg originated from the mine waste calcines, the critical knowledge about the origin of the other heavy metals remains unknown. This study assessed the ecological and health risks from heavy metal pollution surrounding the abandoned Hg mine. Principal component analysis (PCA) showed that the abandoned mine and natural sources (i.e., local geology) are the two main contributors of heavy metal pollution. Historically, the mine waste calcines (retorted ore) were used as construction material for the wharf and as land filler for the adjacent communities. There is highly strong ecological risk associated with the heavy metals: Ni, Hg, Cr, and Mn contribute 44.3%, 29.5%, 10.7%, and 8.9% to the potential ecological risk index (RI), respectively. Hazard index (HI) exceeded 1 for both adults and children in all the sampling locations, implying non-carcinogenic adverse effects. The total cancer risk over a lifetime (LCR) also exceeded the threshold limit of 10−4 for both adults and children, contributed mainly by Cr (91.8%) and As (8.1%). By combining the results of the PCA and risk assessments, a clear link between heavy metal source apportionment to ecological and health risks was established. It was estimated that the abandoned mine contributed to most of the ecological and health risks for people living near the wharf that was built using the calcine, as well as the nearby Honda Bay. The findings of this study are expected to help policy makers develop regulations that will safeguard the ecosystem and the general public from the damaging impacts of heavy metals from the abandoned mine.

Using mercury stable isotope fractionation to identify the contribution of historical mercury mining sources present in downstream water, sediment and fish.

Ecosystems downstream of mercury (Hg) contaminated sites can be impacted by both localized releases as well as Hg deposited to the watershed from atmospheric transport. Identifying the source of Hg in water, sediment, and fish downstream of contaminated sites is important for determining the effectiveness of source-control remediation actions. This study uses measurements of Hg stable isotopes in soil, sediment, water, and fish to differentiate between Hg from an abandoned Hg mine from non-mine-related sources. The study site is located within the Willamette River watershed (Oregon, United States), which includes free-flowing river segments and a reservoir downstream of the mine. The concentrations of total-Hg (THg) in the reservoir fish were 4-fold higher than those further downstream (>90 km) from the mine site in free-flowing sections of the river. Mercury stable isotope fractionation analysis showed that the mine tailings (δ202Hg: -0.36‰ ± 0.03‰) had a distinctive isotopic composition compared to background soils (δ202Hg: -2.30‰ ± 0.25‰). Similar differences in isotopic composition were observed between stream water that flowed through the tailings (particulate bound δ202Hg: -0.58‰; dissolved: -0.91‰) versus a background stream (particle-bound δ202Hg: -2.36‰; dissolved: -2.09‰). Within the reservoir sediment, the Hg isotopic composition indicated that the proportion of the Hg related to mine-release increased with THg concentrations. However, in the fish samples the opposite trend was observed-the degree of mine-related Hg was lower in fish with the higher THg concentrations. While sediment concentrations clearly show the influence of the mine, the relationship in fish is more complicated due to differences in methylmercury (MeHg) formation and the foraging behavior of different fish species. The fish tissue δ13C and Δ199Hg values indicate that there is a higher influence of mine-sourced Hg in fish feeding in a more sediment-based food web and less so in planktonic and littoral-based food webs. Identifying the relative proportion of Hg from local contaminated site can help inform remediation decisions, especially when the relationship between total Hg concentrations and sources do not show similar covariation between abiotic and biotic media.

Total Mercury in Soils and Sediments in the Vicinity of Abandoned Mercury Mine Area in Puerto Princesa City, Philippines

The abandoned mercury (Hg) mine area in Puerto Princesa City, Palawan was included in the list of abandoned and inactive mines in the Philippines which pose a high risk to human health and the environment, and require rehabilitation. The mine site, operated by Palawan Quicksilver Mines, Inc. (PQMI) from 1953 to 1976, is located approximately 3 km inland from Honda Bay coast and within the catchment of the Tagburos River, which is a local fishery and recreational area. In this study, total Hg levels in soils and sediments were measured to assess the possible release of Hg from the site into the surrounding natural environment. Results showed that total Hg (THg) concentrations found in soils (0.04–67.5 mg kg−1), mine waste calcines (52.7–924.2 mg kg−1), river sediments (1.8–119 mg kg−1), and marine sediments (0.04–12.7 mg kg−1) were elevated compared to the global background of 0.045–0.16 mg kg−1. The high concentrations of Hg in soils and river sediments were influenced by the different pathways for the release of Hg from its mine operations; while Hg in marine sediments was caused by the erosion of mine waste calcines near the pit lake, and calcines used to construct a wharf at the nearby Honda Bay. Mine wastes represent the largest source of Hg contamination in the area, due to the low efficiency of the recovery process during calcination. This work corresponds with the Minamata Convention on Mercury on the updated environmental assessments of abandoned Hg mines as potential source sites of mercury contamination.

Evaluation of the potential risks of heavy metal contamination in rice paddy soils around an abandoned Hg mine area in Southwest China

To assess the potential ecological and health risks of trace elements (Hg, Cd, As, Mn, Sb, Pb, Cu, Ni, Cr, and Zn), a total of 138 soil samples from rice paddies were collected during the rice harvest season in the Wanshan mining area, Guizhou Province, Southwest China. Factors of the pollution load index (PLI), geo-accumulation index (I-Geo), enrichment factor (EF), and risk index (RI) were determined. High concentrations of Hg, Sb, As, Zn, Cd, Cu, and Mn were observed in the soils. The PLI, I-Geo, and EF results all showed high levels of contamination by Hg and Sb and moderate levels of contamination by As, Pb, Zn, Cu, Cd, and Mn. There was no significant contamination from Ni and Cr. The RI was very high, with Hg as the dominant pollutant, as expected, indicating that the historical large-scale Hg mining, as well as artisanal mining, has had a significant impact on the Wanshan area. Moreover, coal combustion, manganese factories, and the use of agrochemicals by the local population could also have an impact on the soil through the introduction of heavy metal loads. To address the current state of contamination, pollutant remediation and the regulation control of the anthropogenic activities in Wanshan are urgently needed.

A coupled multivariate statistics, geostatistical and machine-learning approach to address soil pollution in a prototypical Hg-mining site in a natural reserve

The impact of mining activities on the environment is vast. In this regard, many mines were operating well before the introduction of environmental law. This is particularly true of cinnabar mines, whose activity has declined for decades due to growing public concern regarding Hg high toxicity.Here we present the exemplary case study of an abandoned Hg mine located in the Somiedo Natural Reserve (Spain). Until its closure in the 1970s, this mine operated under no environmental regulations, its tailings dumped in two spoil heaps, one of them located uphill and the other in the surroundings of the village of Caunedo. This study attempts to outline the degree to which soil and other environmental compartments have been affected by the two heaps. To this end, we used a novel combination of multivariate statistical, geostatistical and machine-learning methodologies. The techniques used included principal component and clustering analysis, Bayesian networks, indicator kriging, and sequential Gaussian simulations.Our results revealed high concentrations of Hg and, secondarily, As in soil but not in water or sediments. The innovative methodology abovementioned allowed us to identify natural and anthropogenic associations between 25 elements and to conclude that soil pollution was attributable mainly to natural weathering of the uphill heap. Moreover, the probability of surpassing the threshold limits and the local backgrounds was found to be high in a large extension of the area.The methodology used herein demonstrated to be effective for addressing complex pollution scenarios and therefore they are applicable to similar cases.

Environmental assessment of mining industry solid pollution in the mercurial district of Azzaba, northeast Algeria.

To date, there have been few detailed studies regarding the impact of mining and metallogenic activities on solid fractions in the Azzaba mercurial district (northeast Algeria) despite its importance and global similarity with large Hg mines. To assess the degree, distribution, and sources of pollution, a physical inventory of apparent pollution was developed, and several samples of mining waste, process waste, sediment, and soil were collected on regional and local scales to determine the concentration of Hg and other metals according to their existing mineralogical association. Several physico-chemical parameters that are known to influence the pollution distribution are realized. The extremely high concentrations of all metals exceed all norms and predominantly characterize the metallurgic and mining areas; the metal concentrations significantly decrease at significant low distances from these sources. The geo-accumulation index, which is the most realistic assessment method, demonstrates that soils and sediments near waste dumps and abandoned Hg mines are extremely polluted by all analyzed metals. The pollution by these metals decreases significantly with distance, which indicates a limited dispersion. The results of a clustering analysis and an integrated pollution index suggest that waste dumps, which are composed of calcine and condensation wastes, are the main source of pollution. Correlations and principal component analysis reveal the important role of hosting carbonate rocks in limiting pollution and differentiating calcine wastes from condensation waste, which has an extremely high Hg concentration (˃1%).

Arsenic contamination and speciation in surrounding waters of three old cinnabar mines

The impact of arsenic pollution in waters from the surroundings of three abandoned Hg mines in Northern Spain, as well as reaching the Caudal River, was evaluated. For assessing the factors controlling arsenic release, an extensive study based on the physicochemical characterization and multivariate statistical analysis of waters upstream and downstream each mine site was performed. Waters downstream of the La Soterraña mine present the highest arsenic concentrations, up to 38.8 mg L(-1), coming mainly from the solubilisation of calcium, magnesium and strontium arsenates at a pH close to neutral. Although arsenic concentrations downstream of La Peña are markedly lower, these values remain too high, indicating that the encapsulation carried out in this spoil heap is insufficient. In addition, the high water flow in this point involves an extremely high input of arsenic to the surroundings (0.3 g s(-1)). Waters close to tailings from Los Rueldos suffer from acid mine drainage, provoking an important solubilisation of arsenic and heavy metals, a situation which is rapidly softened with distance. The study of arsenic speciation reveals the omnipresence of As(v) in waters from the three mines, whereas in La Peña low amounts of As(iii) were also detected. Different preservation methods for As speciation were compared, such as the addition of HCl, EDTA and the storage of samples without any additive, and no alteration of samples in any case up to nine months after the collection was observed. A study of seasonal variations of As and the main parameters affecting its concentration and speciation was completed throughout a year, showing no remarkable dependency with rainfall for any studied variable.

Surface water monitoring in the mercury mining district of Asturias (Spain)

Systematic monitoring of surface waters in the area of abandoned mine sites constitutes an essential step in the characterisation of pollution from historic mine sites. The analytical data collected throughout a hydrologic period can be used for hydrological modelling and also to select appropriate preventive and/or corrective measures in order to avoid pollution of watercourses. Caudal River drains the main abandoned Hg mine sites (located in Mieres and Pola de Lena districts) in Central Asturias (NW Spain). This paper describes a systematic monitoring of physical and chemical parameters in eighteen selected sampling points within the Caudal River catchment. At each sampling station, water flow, pH, specific conductance, dissolved oxygen, salinity, temperature, redox potential and turbidity were controlled “in situ” and major and trace elements were analysed in the laboratory. In the Hg-mineralised areas, As is present in the form of As-rich pyrite, realgar and occasionally arsenopyrite. Mine drainage and leachates from spoil heaps exhibit in some cases acidic conditions and high As contents, and they are incorporated to Caudal River tributaries. Multivariate statistical analysis aids to the interpretation of the spatial and temporary variations found in the sampled areas, as part of a methodology applicable to different environmental and geological studies.

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.

Impact of mining activities on soils and sediments at the historical mining area in Podljubelj, NW Slovenia

The abandoned Hg mine in Podljubelj was in operation with interceptions from 1557 to 1902. The entire operating period yielded about 110 000 tons of ore, from which 360 tons of Hg was produced. The objective of the research project was to establish the contents and spatial distribution of Hg in soils and stream sediments in the vicinity of the mine. On an area of 88 ha the soil was sampled in a 100 × 100 m grid. Two soil horizons (0–5 cm and 20–30 cm) were sampled in order to distinguish between geogenic and anthropogenic Hg sources. It was established that on an area of about 9 ha Hg content in soil exceeds The New Dutchlist action value for Hg (10 mg/kg). Total Hg concentrations in soil samples vary between 0.17 and 719 mg/kg, with a mean of 3.0 mg/kg. Mercury contents in stream sediments range from 0.065 to 1.4 mg/kg, with a mean of 0.64 mg/kg. The highest determined value in soils was found in the area around the former roasting furnace, where the ore was processed. Increased Hg concentrations were also found on the mine waste dump (108 mg/kg). Mercury contents in soils generally decrease with soil profile depth and with the distance from the mine and from the roasting furnace location. Mercury also appears in higher concentrations along the road that runs through the valley, which results from the use of Hg-bearing ore residues in road construction. The average enrichment factor (EF) of Hg in topsoil with respect to subsoil is 3.3. Calculated enrichment factors show higher values also for Cd (3.2), Pb (2.7), Ca (2.4) and P (1.9). The average enrichment factor of Hg in topsoil with regard to the established Slovenian soil averages (EF slo) is 19. EF slo of other determined chemical elements do not exceed 3.0.

Evaluation of the water quality related to the acid mine drainage of an abandoned mercury mine (Alaşehir, Turkey)

Mobility of metals in water, mine wastes, and stream sediments around the abandoned Alaşehir mercury mine was investigated to evaluate the environmental effects around the area. Mine waters are dominantly acidic with pH values of 2.55 in arid season and 2.70 in wet season and are sulfate rich. Acidity is caused mainly by the oxidation of sulfide minerals. Pyrite is the main acid-producing mineral in the Alaşehir area. Of the major ions, SO(4) shows a notable increase reaching 3981 mg/l, which exceeds the WHO (WHO guidelines for drinking water quality, vol. 2. Health criteria and other supporting information, 1993) and TS (Sular-Içme ve kullanma sulari. Ankara: Türk Standartlari Enstitüsü, 1997) drinking water standard of 250 mg/L. Mine waters have As, Fe, Mn, Ni, and Al with concentrations higher than drinking water standards. Hg concentrations of adit water samples and surface waters draining the mine area are between 0.25 and 0.274 microg/L and are below the WHO (WHO guidelines for drinking water quality, vol. 2. Health criteria and other supporting information, 1993) drinking water standard of 1.0 microg/L. However, the concentrations are above the 0.012 microg/L standard (EPA, Water quality standards. Establishment of numeric criteria for priority toxic pollutants, states' compliance, final rule. Fed. Reg., 40 CFR, Part 131, 57/246, 60847-60916, 1992) used to protect aquatic life. Stream sediment samples have abnormally high values of especially Hg, As, Ni, and Cr metals. Geoaccumulation (Igeo) and pollution index (PI) values are significantly high and denote heavy contamination in stream sediments. The stream sediments derived from the mining area with the surface waters are potentially hazardous to the environment adjacent to the abandoned Hg mine and are in need of remediation.

Assessment of the Pollutants in Farming Soils and Waters Around Untreated Abandoned Türkönü Mercury Mine (Turkey)

There are several abandoned Hg mines located in western Turkey. Hg production in these mines was eventually halted in the early 1990 s because of low prices and environmental concerns (Gemici, 2004). However, acid mine drainage waste causes potential environmental problems near the Hg mines. In Türkönü Hg mine (Fig. 1) nearly 7,000 flasks of mercury had been produced in recent years. In 1965 a private company began to investigate the deposit and by 1968 had installed a 100-tpd rotary furnace. Since, the ore supply has been inadequate and the furnace plant used to process ore hauled from other deposits. Mercury production was terminated in 1975, owing to low prices, and in 1976 the furnace plant was used to process antimony ore (Yildiz and Bailey, 1978). Areas near the mine are currently being used for agricultural purposes. Soils are directly influenced by contaminants, leaching from the mine wastes, which are transported by surface waters in the rainy season. The aim of this study is to evaluate the geochemical dispersal within soil and water,of Hg derived from the abandoned Türkönü mine relating to past mining activities.

Mercury methylation influenced by areas of past mercury mining in the Terlingua district, Southwest Texas, USA

Speciation and microbial transformation of Hg was studied in mine waste from abandoned Hg mines in SW Texas to evaluate the potential for methyl-Hg production and degradation in mine wastes. In mine waste samples, total Hg, ionic Hg 2+, Hg 0, methyl-Hg, organic C, and total S concentrations were measured, various Hg compounds were identified using thermal desorption pyrolysis, and potential rates of Hg methylation and methyl-Hg demethylation were determined using isotopic-tracer methods. These data are the first reported for Hg mines in this region. Total Hg and methyl-Hg concentrations were also determined in stream sediment collected downstream from two of the mines to evaluate transport of Hg and methylation in surrounding ecosystems. Mine waste contains total Hg and methyl-Hg concentrations as high as 19,000 μg/g and 1500 ng/g, respectively, which are among the highest concentrations reported at Hg mines worldwide. Pyrolysis analyses show that mine waste contains variable amounts of cinnabar, metacinnabar, Hg 0, and Hg sorbed onto particles. Methyl-Hg concentrations in mine waste correlate positively with ionic Hg 2+, organic C, and total S, which are geochemical parameters that influence processes of Hg cycling and methylation. Net methylation rates were as high as 11,000 ng/g/day, indicating significant microbial Hg methylation at some sites, especially in samples collected inside retorts. Microbially-mediated methyl-Hg demethylation was also observed in many samples, but where both methylation and demethylation were found, the potential rate of methylation was faster. Total Hg concentrations in stream sediment samples were generally below the probable effect concentration of 1.06 μg/g, the Hg concentration above which harmful effects are likely to be observed in sediment dwelling organisms; whereas total Hg concentrations in mine waste samples were found to exceed this concentration, although this is a sediment quality guideline and is not directly applicable to mine waste. Although total Hg and methyl-Hg concentrations are locally high in some mine waste samples, little Hg appears to be exported from these Hg mines in stream sediment primarily due to the arid climate and lack of precipitation and mine runoff in this region.

Environmental impact of toxic metals and metalloids from the Muñón Cimero mercury-mining area (Asturias, Spain)

This paper presents the results of the sampling surveys carried out in order to evaluate the environmental problems associated to La Soterraña, an abandoned Hg mine in Asturias, north of Spain. In particular, this paper overviews the impact of mining and metallurgical activities on terrestrial and aquatic environments. The wastes generated during the mining activity (ore extraction and processing) and later accumulated on the ground, contain great amount of sulphides, becoming potentially acid-generating. Consequently, the mobility of heavy metals and other ecotoxic elements is enhanced. Wastes are generally located close to watercourses and on very steep hillsides, where they are exposed to oxidative weathering, posing a significant risk due to the release of ecotoxic elements to the environment. Background levels were determined at sites, which had not been directly affected by mercury mining. A multielemental geochemical study of mining wastes, soils, stream sediments, water and air samples collected in the area of influence of the old mining and metallurgical works was carried out. Total Hg and As concentrations in soils reach values up to 502 and 19,940 mg kg −1, respectively, 500 and 2000 times higher than the local background levels. The effects of mining seem to be intense both in waters and stream sediments, as well as in the local atmosphere, whose Hg content is 10 times higher than the background level in the area. Therefore, the target carcinogenic risk was exceeded for As and Hg in La Soterraña site.

Physicochemical characterization and mercury speciation of particle-size soil fractions from an abandoned mining area in Mieres, Asturias (Spain)

Soils from old cinnabar mining areas usually exhibit high Hg contents, whose mobility depends on soil parameters and environmental conditions. This paper presents the study of the Hg speciation in soil samples from an abandoned Hg mine and metallurgical plant in Mieres (Asturias, Spain), in relation to their mineralogical and chemical composition and their particle-size distribution. A characterization of samples was made by X-Ray Diffraction Spectrometry, Scanning Electron Microscopy and Atomic Absorption and Emission Spectroscopy analyses. A sequential extraction method was applied to establish Hg mobility in the samples and their grain-size subsamples. The highest Hg mobility was found in well-developed soils, as a consequence of the adsorption processes by iron and manganese oxides, whereas in those more contaminated soils, a higher proportion of Hg was leached in the non-mobile fraction. A higher Hg mobility was found in the finest grain-size subsamples, probably due to the accumulation of clay minerals and oxides in these ranges.

Mercury and methylmercury in riparian soil, sediments, mine-waste calcines, and moss from abandoned Hg mines in east Guizhou province, southwestern China

Concentrations of total Hg and methylmercury (MMHg) in riparian soil, mine-waste calcine, sediment, and moss samples collected from abandoned Hg mines in Wanshan district, Guizhou province, China, were measured to show regional dispersion of Hg-contamination. High total Hg and MMHg concentrations obtained in riparian soils from mined areas, ranged from 5.1 to 790 mg kg −1 and 0.13 to 15 ng g −1, respectively. However, total Hg and MMHg concentrations in the soils collected from control sites were significantly lower varying from 0.1 to 1.2 mg kg −1 and 0.10 to 1.6 ng g −1, respectively. Total Hg and MMHg concentrations in sediments varied from 90 to 930 mg kg −1 and 3.0 to 20 ng g −1, respectively. Total Hg concentrations in mine-waste calcines were highly elevated ranging from 5.7 to 4400 mg kg −1, but MMHg concentrations were generally low ranging from 0.17 to 1.1 ng g −1. Similar to the high Hg concentrations in soil and sediments, moss samples collected from rocks ranged from 1.0 to 95 mg kg −1 in total Hg and from 0.21 to 20 ng g −1 in MMHg. Elevated Hg concentrations in mosses suggest that atmospheric deposition might be an important pathway of Hg to the local terrestrial system. Moreover, the spatial distribution patterns of Hg contamination in the local environment suggest derivation from historic Hg mining sites in the Wanshan area.

Mercury methylation in mine wastes collected from abandoned mercury mines in the USA

Mercury mines contain highly elevated Hg contents, but more problematic environmentally are elemental Hg and soluble Hg salts produced during ore retorting that remain in wastes at mine sites. Under certain conditions, these inorganic Hg compounds convert to bioavailable, highly toxic organic Hg forms. Speciation and transformation of Hg was studied in wastes collected from abandoned Hg mines at McDermitt, NV, and Terlingua, TX, which are moderate size on an international scale and produced about 10,000 and 5,000 t of elemental Hg, respectively. In waste samples, we measured total Hg and methyl-Hg contents, identified various Hg compounds using Hg-thermo-desorption pyrolysis, and determined rates of Hg methylation and methyl-Hg demethylation using isotopic-tracer methods. Pyrolysis analysis of mine wastes showed variable amounts of cinnabar, metacinnabar, Hg salts, elemental Hg, and elemental Hg sorbed onto particulates such as clay and Fe-oxides. Mine wastes with the highest methyl-Hg contents correspond to those with elemental Hg and particulate-sorbed elemental Hg, and also produced the highest laboratory-estimated potential Hg methylation rates, as much as 4.8%/day. Samples containing dominantly cinnabar showed little or no Hg methylation. Mine wastes with high methyl-Hg contents generally showed low methyl-Hg demethylation, suggesting that Hg methylation was dominant. Both mines are locatedmore » in semiarid climates, and during this study, streambeds below the mines were dry. Total Hg contents in stream sediment collected below the mines show significant dilution, and methyl-Hg contents were typically below the limit of determination. Methylation of Hg downstream from Hg mines is probably lower in arid climates due to lack of mine-water runoff and lower microbial activity. The correspondence of mine wastes containing elemental Hg and high methyl-Hg contents suggests that Hg0 oxidizes to Hg2+, which is subsequently bioavailable for microbial Hg methylation.« less

Environmental geochemistry of abandoned mercury mines in West-Central Nevada, USA

The Humboldt River is a closed basin and is the longest river in Nevada. Numerous abandoned Hg mines are located within the basin, and because Hg is a toxic heavy metal, the potential transport of Hg from these mines into surrounding ecosystems, including the Humboldt River, is of environmental concern. Samples of ore, sediment, water, calcines (roasted ore), and leachates of the calcines were analyzed for Hg and other heavy metals to evaluate geochemical dispersion from the mines. Cinnabar-bearing ore samples collected from the mines contain highly elevated Hg concentrations, up to 6.9 %, whereas calcines collected from the mines contain up to 2000 mg Hg/kg. Stream-sediment samples collected within 1 km of the mines contain as much as 170 mg Hg/kg, but those collected distal from the mines (>5 km) contain <1 mg Hg/kg, indicating significant geochemical dispersion of Hg downstream from the mines. Sediment samples collected from the Humboldt River basin contain ⩽0.28 mg Hg/kg. Leachate samples of the calcines obtained by using a synthetic water leaching technique contain as much as 1500 μg Hg/l, suggesting that some calcines contain soluble Hg compounds. However, much lower Hg concentrations were found in water samples collected from the Humboldt River system, and these were below the 0.012 μg/l Hg standard used to protect against chronic effects to aquatic wildlife. Mercury transference from these mines to the Humboldt River basin is generally minor because the mines are typically >8 km from the Humboldt River, and Hg is transported and diluted through a large volume of pediment before it reaches the Humboldt River.

Mercury bioaccumulation in a stream fish population residing in the vicinity of an abandoned Hg mine

Mercury bioaccumulation in a stream fish population residing in the vicinity of an abandoned Hg mine