G6 Impacts of mining

Between 1564 and 1810, approximately 17,000 metric tons of mercury vapor were released into the atmosphere as a result of cinnabar smelting operations in Huancavelica, Peru. In Potosí (present-day Bolivia) nearly 39,000 metric tons of mercury were volatized as a result of amalgamation-based silver refining operations between 1574 and 1810. Mercury emissions from cinnabar refining and silver production were estimated from detailed Spanish records from the colonial period and locations and sources characteristics were derived from archival images, maps, and first-hand assessments of cinnabar refining mills and silver smelters . AERMOD, a state-of-the-art air dispersion model, was used to estimate historical ambient air concentrations of mercury in vapor phase from colonial mining and refining operations during periods of high, medium, and low production periods in Huancavelica and Potosí. The modeled 1-hour maximum concentrations exceeded inhalation reference values in locations near the smelter, highlighting the health hazards to the historical population due to exposure to elemental mercury vapor. AERMOD results were then used to select sampling locations along transects in Huancavelica and Potosí to evaluate present-day soil concentrations of mercury and other metals from historical mercury refining operations. All soil samples contained mercury, with total concentrations in Potosí reaching 250 mg/kg and 1,200 mg/kg in Huancavelica. Mercury concentrations in the soil were 10 to 70,000 times greater than in a non-mining city in Bolivia. Preliminary data also indicated other metal co-contaminants in the soil, including silver and lead. These results indicate that residents currently living in Potosí and Huancavelica are exposed to high concentrations of mercury and perhaps other metals from historical contamination that may present significant health risks today. Disclaimer: The views expressed in this abstract are those of the authors and do not represent US EPA policy.

Between 1564 and 1810, nearly 17,000 metric tons of mercury vapor were released in Huancavelica, Peru, as a consequence of cinnabar smelting operations. As a result of atmospheric transport and transformation, mercury deposited in the local community, contaminating all compartments of the environment. Soil concentrations in the community have been measured to contain up to 1,200 mg/kg of mercury, among the highest levels measured in surface soil in the world. Residents in Huancavelica have constructed their adobe homes using this soil, prompting an investigation of residential exposure to mercury. Homes in Huancavelica were sampled for mercury in different media, including air (vapor and particulates), surface dust wipes, and adobe bricks. For the first 10 homes in the study, mercury was detected in varying concentrations in all media sampled. Mercury vapor concentrations in the homes were up to 5.5 µg/m³, while particulate samples were as high as 0.49 µg/m³. Adobe brick on the interior of the walls had measured mercury concentrations up to 780 mg/kg. This poses a significant health risk to the residents of Huancavelica, especially women and children, who spend a majority of their time in their homes. The median uptake by a 1-year-old toddler is 100 mg of dirt and dust ingested per day from hand-to-mouth activity. For this ingestion rate, the daily exposure for an 11 kg 1-year-old toddler (50^th percentile body weight for U.S. males and females) would exceed EPA’s Reference Dose (RfD) for inorganic mercury (0.3 mg/kg-day) if the ingested soil and dust contained more than 33 mg/kg of mercury. In Huancavelica, the ingestion of dirt and dust is not only a result of time spent outdoors, but exposure potential is amplified by the concentrations present in homes. It is important to consider that the ingestion rate and body weight are for U.S. children; children in Huancavelica and South America in general may have different ingestion rates and body weights. Not only do children have potentially higher levels of mercury exposure than adults, but the likelihood and severity of adverse health effects are greater as well, as their brains and neurological systems are still developing. A comprehensive analysis of mercury contamination in Huancavelica will guide the development of mitigation and remediation strategies informed by community-based participatory research to reduce the health risks from residential mercury exposure. Disclaimer: The views expressed in this abstract are those of the authors and do not represent US EPA policy.

The Cache Creek Settling Basin (CCSB) is a levee-bounded area of about 14.5 km² that traps sediment in Cache Creek (CC), which drains a coastal mountain watershed that has high mercury (Hg) concentrations. The Hg in CC comes from both natural sources (hot springs and erosion of hydrothermally altered rocks) and anthropogenic sources (wastes from historical Hg and gold mines). The CCSB discharges into the Yolo Bypass, a conveyance that protects the city of Sacramento and adjacent areas from flooding of the Sacramento River. In the Sacramento River watershed, which is the predominant source of water and Hg to the Sacramento-San Joaquin Delta, flow through the CCSB accounts for about 2% of the water balance but about 30% of the Hg load. The CCSB currently traps about one-half to two-thirds of the load of suspended sediment (SS) and total Hg (THg) from CC; however, the budgets for methylmercury (MeHg) and reactive Hg(II) (Hg(II)_R) are unknown. Because of seasonal wet-dry cycles (typical rainfall November-April and agricultural irrigation June-September), there is concern that riparian wetlands and agricultural fields within the CCSB are favorable areas for Hg(II) methylation. Streamgages at the inflow, outflow gate, and overflow weir of the CCSB have been monitored for discharge and SS concentration since January 2009, and daily SS loads have been quantified. Water-quality sampling and analysis of THg, MeHg, Hg(II)_R, dissolved organic carbon (DOC) concentration, and grain-size distribution in SS of CCSB inflows and outflows began in January 2010. Continuous monitoring of turbidity with in-situ probes is providing data on temporal variation in SS concentration, especially during storm events. Spatial and temporal variations in bed-sediment THg, MeHg, and Hg(II)_R concentrations are being assessed at selected riparian and agricultural sites within the CCSB during 2010-2011. Preliminary results of water-quality sampling indicate that the CCSB is a net source of MeHg and DOC during periods of moderate flow between storm events (for example, February to March 2010). Concentrations of THg and Hg(II)_R in unfiltered water correlated positively with SS concentration, turbidity, and discharge during January to May 2010, reinforcing the utility of continuous monitoring for development of accurate budgets for THg and Hg(II)_R. Aqueous concentrations of MeHg did not show similar correlations, causing relatively higher uncertainty in calculated MeHg loads. A preliminary conceptual model for Hg cycling in the CCSB involves deposition of THg and Hg(II)_R during storm flows, with subsequent methylation of Hg(II)_R and export of MeHg.

Historical stamp milling and Hg amalgamation activities at lode gold mines in Nova Scotia have generated tailings deposits containing Hg, As, and other potentially toxic elements. From 1861 to the mid-1940s, gold was produced from 64 mining districts in the southern part of the province, resulting in approximately 3 million tonnes of tailings. Most of the gold was recovered using Hg amalgamation, and an estimated 9000 kg of Hg were lost to the tailings and to the atmosphere. Tailings from these operations were generally slurried into local rivers, swamps, lakes, and the ocean. This presentation will summarize results from recent multi-disciplinary studies of the distribution, mobility, and fate of Hg in terrestrial and marine environments surrounding abandoned gold mines throughout Nova Scotia. Between 2003 and 2007, samples of tailings, soil, till, rock, sediment, and surface water were collected at 15 past-producing mines. Chemical analyses of 77 near-surface soils overlying mineralized bedrock in these gold districts show that baseline Hg concentrations range from approximately 0.06-0.49 mg/kg (median 0.14 mg/kg). In contrast, analyses of total Hg concentrations in more than 400 samples of tailings range from 0.01-350 mg/kg (median 2.0 mg/kg), with Hg concentrations <1.0 mg/kg restricted to sites where cyanidation was used as the primary method of gold extraction. Sequential extraction analyses show that Hg in tailings and contaminated stream sediments is present in elemental form (Hg⁰), amalgam (Au_xHg_x), secondary phases (e.g. HgS), and is sorbed to Fe-oxides and organic matter. Measurements of gaseous Hg in ambient air over two tailings sites showed continuous diurnal Hg evasion at the soil surface. Surface waters in these mine districts are generally circumneutral, and dissolved Hg concentrations are relatively low (1.2-61 ng/L; median 10 ng/L; n=181) at all sites. Concentrations of methylmercury are high in tailings and pore waters, but low in overlying surface waters. Methylmercury concentrations are highly variable, and influenced by a complex set of in situ factors including total Hg concentrations in the tailings and pore waters, organic content, hydrological conditions, abundance and activity of sulfate-reducing bacteria, and demethylation processes. Biological sampling has demonstrated that Hg has bioaccumulated to various degrees in freshwater and marine biota, including perch, eels, clams, and mussels. Results from these studies have been used by the Nova Scotia Historic Gold Mines Advisory Committee to assess the human and ecological health risks associated with these sites, and to help guide risk-management decisions.

Cinnabar ore reserves in China ranks the third largest and most of Hg mines in the region currently abandoned because of the increasing environmental issue. The primary concern on Hg mines is the biological accumulation of Hg in local environmental compartments, namely the conversion from inorganic to organic Hg, such as methylmercury (MeHg). Approximately 10 abandoned Hg mines as well as a living Hg mine, distributed over 5 provinces were selected for investigation of total mercury (THg) and MeHg in soil, surface water, and vegetations. Atmospheric Hg concentrations (TGM) in ambient air in those Hg mining areas were also investigated with Tekran 2537A and Lumex RA915⁺. By adding isotope of ²⁰²Hg⁺⁺ and Me¹⁹⁸Hg⁺, the rate of Hg methylation/demethylation in paddy soil and surface water were calculated. The preliminary results indicated that high MeHg concentrations (up to 20 µg kg^-1) were observed in paddy soil, exhibiting a high rate of Hg methylation/demethylation (k_d value ranged from 0.13x10^-3 to 0.83x10^-3 d^-1). The rice plant could uptake and accumulate high levels of MeHg (up to 170 µg kg^-1) its edible part. Though Hg mines abandoned 10 years, mine tailing were still as the dominant emission source of atmospheric Hg in ambient air.

Across the globe there are aquatic ecosystems impacted by ongoing and the historic use of elemental mercury (Hg) for gold extraction. The headwaters of Steamboat Creek (SBC), a major tributary of the Truckee River Nevada/California USA, were, in the 1800’s, a location where Hg was used to extract gold and silver from ore. The impacts of this activity remain to this day in the creek and the river as demonstrated by concentrations of Hg in fish that exceed the US EPA consumption advisory. Additionally, Hg concentrations in water, sediment and macroinvertebrates below the confluence of the creek are elevated relative to those measured upriver. We investigated the distribution of Hg in abiotic and biotic components along the length of the river, as well as the potential for Hg concentrations in water, sediments and macroinvertebrates to be latent indicators of potential sources of methylmercury (MeHg) for fish species. Fish Hg concentrations increased down river as did filtered water MeHg concentrations and those in some macroinvertebrate species (Caddisflies, Mayflies, Crayfish, Aq. Earthworms, and Flatworm). In general, sediments associated with the river shore and a restoration area had higher MeHg concentrations and as such these environments are likely a source of MeHg to the water column during high flow conditions. Specific macroinvertebrates (Water striders and Damselflies) that frequent these areas also had a Hg concentration trend similar to sediments. Mercury inputs to the river are primarily as particulate bound form. Mercury concentrations in sediments showed that deposition of Hg is important in the shore environments where often fine particulate bound Hg may settle, water is slow moving and even stagnant, and more vegetation is present, promoting MeHg production.

Mercury (Hg) has been emitted from a base metal smelter in the town of Flin Flon, MB, Canada from the 1930s up until June, 2010 when the smelter was closed. During the last decade, the smelter had emitted on average 1093±261 Kg/year, resulting in elevated Hg concentrations in the surrounding soils (2.8 ± 1.5 to 560 ± 72 µg/g) (NPRI database; Manitoba Conservation, 2007). The main objective of this project was to measure Hg fluxes from natural surfaces surrounding the smelter (as well as un-impacted reference locations) before and after the smelter’s closure to identify the relationship between air Hg concentrations, deposition and re-emission. Hg fluxes were measured using the dynamic flux chamber (DFC) technique from several locations during two intensive field sampling campaigns both before and three months after the smelter closure. In addition, controlled laboratory experiments were conducted using soils from the Flin Flon area to identify the pool of surface associated Hg that is available for emission. The results of the field measurements showed that while the smelter was in operation, the ambient air concentrations measured at the DFC inlet were large and variable (30 ± 19 ng/m³) relative to concentrations at the un-impacted reference (1.6 ± 0.3m ng/m³). Following smelter closure, the air concentrations near the smelter dropped significantly to 7.5 ± 3.3 ng/m³ (though were still elevated above background concentrations). The Hg fluxes measured from the reference site followed a clear diel trend—with higher emissions during the daytime (3.5 ng/m²/h) than at night (-0.3 ng/m²/h). While the smelter was in operation, the Hg fluxes near the smelter were much larger than at the reference site and did not follow a diel trend (-28 to 460 ng/m²/h)—fluxes varied between net emission and deposition related to prevailing wind direction from the smelter/air Hg concentrations. However, following the smelter closure, a clear diel trend in the Hg fluxes was observed from impacted areas near the smelter (59 to 338 ng/m²/h), which were all net emission and had maximum daily fluxes that were of similar magnitude as observed during the smelter operation. Overall, these results identify how surface Hg fluxes change with distance from the smelter as well as how fluxes change over time following the cessation of emissions from a large point source emitter.

The influence of zinc smelter and abandened metal mines known as major Hg emission sources on the environmental pollution and human exposure was investigated in some regions. Smelter in this survey was estimated to emit about 2.7 and 2kg/year of Hg into the air(emission factor 9.99mg/ton) and river respectively. There are 50 abandened metal mines in mountains near the river. Atmospheric Hg of two spots (near smelter, 50km away), mercury in soil and fish, crops, drinking water were measured. Questionnaire was implemented to examine the association of environment and human exposure of mercury. The survey was mainly done in the down stream region closed to river (1km). The results were compared with those of region far from the river (over 3Km). Atmospheric total gaseous and particulate mercury were 5.64 and 2.19ng/m³, 83.3 and 85pg/m³. Mercury in soil and drinking water of areas near river (survey areas) were 0.011mg/kg and 1.76ng/L. Those of areas far from the river (contrasted areas) were 0.008 and 2.04. Fish Hg concentration(µg/g-dry weight, 3 species) near smelter was 0.137 that are lower than those of down stream (0.231). Rice didn’t show concentration difference. Blood and urine mercury of residents in survey area were 3.13µg/L and 1.91µg/g-creatinine which were higher than those of contrasted area (3.12, 1.49). The proximity of residential area to river, self-cultivation of rice and residential periods, types of drinking water didn’t have any relation to the mercury exposure. But urine mercury of the people living near smelter was 4.59 µg/g-creatinine which was 2 times higher than that of people living in the regions 50Km far from the smelter. The men who eat frequently the fish catched from river showed higher blood mercury level(4.92µg/L) than that of the men didn’t(3.97µg/L). In conclusion the mercury from smelter and abandened mines have influenced on human exposure via atmospheric and fish contamination.