James G. Crock

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

Abstract 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 8 km from the Humboldt River, and Hg is transported and diluted through a large volume of pediment before it reaches the Humboldt River.

In vitro studies evaluating leaching of mercury from mine waste calcine using simulated human body fluids.

In vitro bioaccessibility (IVBA) studies were carried out on samples of mercury (Hg) mine-waste calcine (roasted Hg ore) by leaching with simulated human body fluids. The objective was to estimate potential human exposure to Hg due to inhalation of airborne calcine particulates and hand-to-mouth ingestion of Hg-bearing calcines. Mine waste calcines collected from Hg mines at Almadén, Spain, and Terlingua, Texas, contain Hg sulfide, elemental Hg, and soluble Hg compounds, which constitute primary ore or compounds formed during Hg retorting. Elevated leachate Hg concentrations were found during calcine leaching using a simulated gastric fluid (as much as 6200 μg of Hg leached/g sample). Elevated Hg concentrations were also found in calcine leachates using a simulated lung fluid (as much as 9200 μg of Hg leached/g), serum-based fluid (as much as 1600 μg of Hg leached/g), and water of pH 5 (as much as 880 μg of Hg leached/g). The leaching capacity of Hg is controlled by calcine mineralogy; thus, calcines containing soluble Hg compounds contain higher leachate Hg concentrations. Results indicate that ingestion or inhalation of Hg mine-waste calcine may lead to increased Hg concentrations in the human body, especially through the ingestion pathway.

Rare earth elements in the phosphatic-enriched sediment of the Peru shelf

Abstract Apatite-enriched materials from the Peru shelf have been analyzed for their major oxide and rare earth element (REE) concentrations. The samples consist of (1) the fine fraction of sediment, mostly clay material, (2) phosphatic pellets and fish debris, which are dispersed throughout the fine-grained sediment, (3) tabular-shaped phosphatic crusts, which occur within the uppermost few centimeters of sediment, and (4) phosphatic nodules, which occur on the seafloor. The bulk REE concentrations of the concretions suggest that these elements are partitioned between the enclosed detrital material and the apatite fraction. Analysis of the fine-grained sediment with which the samples are associated suggested that this detrital fraction in the concretions should have shale REE values; the analysis of the fish debris suggested that the apatite fraction might have seawater values. The seawater contribution of REEs is negligible in the nodules and crust, in which the apatite occurs as a fine-grained interstitial cement. That is, the concentration of REEs and the REE patterns are predominantly a function of the amount of enclosed fine-grained sediment. By contrast, the REE pattern of the pelletal apatite suggests a seawater source and the absolute REE concentrations are relatively high. The REE P 2 O 5 ratios of the apatite fraction of these samples thus vary from approximately zero (in the case of the crust and nodules) to as much as approximately 1.2 × 10−3 (in the case of the pellets). The range of this ratio suggests that rather subtle variations in the depositional environment might cause a significant variation in the REE content of this authigenic fraction of the sediment. Pelletal glauconite was also recovered from one sediment core. Its REE concentrations closely resemble those of the fish debris.

Linking geological and health sciences to assess childhood lead poisoning from artisanal gold mining in Nigeria.

Background: In 2010, Médecins Sans Frontières discovered a lead poisoning outbreak linked to artisanal gold processing in northwestern Nigeria. The outbreak has killed approximately 400 young children and affected thousands more. Objectives: Our aim was to undertake an interdisciplinary geological- and health-science assessment to clarify lead sources and exposure pathways, identify additional toxicants of concern and populations at risk, and examine potential for similar lead poisoning globally. Methods: We applied diverse analytical methods to ore samples, soil and sweep samples from villages and family compounds, and plant foodstuff samples. Results: Natural weathering of lead-rich gold ores before mining formed abundant, highly gastric-bioaccessible lead carbonates. The same fingerprint of lead minerals found in all sample types confirms that ore processing caused extreme contamination, with up to 185,000 ppm lead in soils/sweep samples and up to 145 ppm lead in plant foodstuffs. Incidental ingestion of soils via hand-to-mouth transmission and of dusts cleared from the respiratory tract is the dominant exposure pathway. Consumption of water and foodstuffs contaminated by the processing is likely lesser, but these are still significant exposure pathways. Although young children suffered the most immediate and severe consequences, results indicate that older children, adult workers, pregnant women, and breastfed infants are also at risk for lead poisoning. Mercury, arsenic, manganese, antimony, and crystalline silica exposures pose additional health threats. Conclusions: Results inform ongoing efforts in Nigeria to assess lead contamination and poisoning, treat victims, mitigate exposures, and remediate contamination. Ore deposit geology, pre-mining weathering, and burgeoning artisanal mining may combine to cause similar lead poisoning disasters elsewhere globally.

Mercury methylation at mercury mines in the Humboldt River Basin, Nevada, USA

Total Hg and methylmercury concentrations were measured in mine-waste calcines (retorted ore), sediment, and water samples collected in and around abandoned mercury mines in western Nevada to evaluate Hg methylation at the mines and in the Humboldt River Basin. Mine-waste calcines contain total Hg concentrations as high as 14 000 μg g−1. Stream-sediment samples collected within 1 km of the mercury mines contain total Hg concentrations as high as 170 μg g−1, whereas stream sediments collected at a distance >5 km from the mines, and those collected from the Humboldt River and regional baseline sites, contain total Hg concentrations <0.5 μg g−1. Similarly, methylmercury concentrations in mine-waste calcines are locally as high as 96 ng g−1, but methylmercury contents in stream sediments collected downstream from the mines and from the Humboldt River are lower, ranging from <0.05 to 0.95 ng g−1. Stream-water samples collected downstream from two mines studied contain total Hg concentrations ranging from 6 to 2000 ng l−1, whereas total Hg in Humboldt River water was generally lower, ranging from 2.1 to 9.0 ng l−1. Methylmercury concentrations in the Humboldt River water were the lowest in this study (<0.02–0.27 ng l−1). Although total Hg and methylmercury concentrations are locally high in mine-waste calcines, there is significant dilution of Hg and there is also lower Hg methylation down gradient from the mines, especially in the sediments and water collected from the Humboldt River, which is >8 km from the nearest mercury mines. Our data indicate little transference of Hg and methylmercury from the sediment to the water column due to the lack of mine runoff in this desert climate.

Exposure of insects and insectivorous birds to metals and other elements from abandoned mine tailings in three Summit County drainages, Colorado

Concentrations of 31 metals, metalloids, and other elements were measured in insects and insectivorous bird tissues from three drainages with different geochemistry and mining histories in Summit Co., Colorado, in 2003, 2004, and 2005. In insect samples, all 25 elements that were analyzed in all years increased in both Snake and Deer Creeks in the mining impacted areas compared to areas above and below the mining impacted areas. This distribution of elements was predicted from known or expected sediment contamination resulting from abandoned mine tailings in those drainages. Element concentrations in avian liver tissues were in concordance with levels in insects, that is with concentrations higher in mid-drainage areas where mine tailings were present compared to both upstream and downstream locations; these differences were not always statistically different, however. The lack of statistically significant differences in liver tissues, except for a few elements, was due to relatively small sample sizes and because many of these elements are essential and therefore well regulated by the bird’s homeostatic processes. Most elements were at background concentrations in avian liver tissue except for Pb which was elevated at mid-drainage sites to levels where δ-aminolevulinic acid dehydratase activity was inhibited at other mining sites in Colorado. Lead exposure, however, was not at toxic levels. Fecal samples were not a good indication of what elements birds ingested and were potentially exposed to.

Mercury in mosses Hylocomium splendens (Hedw.) B.S.G. and Pleurozium schreberi (Brid.) Mitt. from Poland and Alaska: understanding the origin of pollution sources.

This report shows baseline concentrations of mercury in the moss species Hylocomium splendens and Pleurozium schreberi from the Kielce area and the remaining Holy Cross Mountains (HCM) region (south-central Poland), and Wrangell-Saint Elias National Park and Preserve (Alaska) and Denali National Park and Preserve (Alaska). Like mosses from many European countries, Polish mosses were distinctly elevated in Hg, bearing a signature of cross-border atmospheric transport combined with local point sources. In contrast, Alaskan mosses showed lower Hg levels, reflecting mostly the underlying geology. Compared to HCM, Alaskan and Kielce mosses exhibited more uneven spatial distribution patterns of Hg. This variation is linked to topography and location of local point sources (Kielce) and underlying geology (Alaska). Both H. splendens and P. schreberi showed similar bioaccumulative capabilities of Hg in all four study areas.

Predicting toxic effects of copper on aquatic biota in mineralized areas by using the Biotic Ligand Model

The chemical speciation of metals influences their biological effects. The Biotic Ligand Model (BLM) is a computational approach to predict chemical speciation and acute toxicological effects of metals on aquatic biota. Recently, the U.S. Environmental Protection Agency incorporated the BLM into their regulatory waterquality criteria for copper. Results from three different laboratory copper toxicity tests were compared with BLM predictions for simulated test-waters. This was done to evaluate the ability of the BLM to accurately predict the effects of hardness and concentrations of dissolved organic carbon (DOC) and iron on aquatic toxicity. In addition, we evaluated whether the BLM and the three toxicity tests provide consistent results. Comparison of BLM predictions with two types of Ceriodaphnia dubia toxicity tests shows that there is fairly good agreement between predicted LC50 values computed by the BLM and LC50 values determined from the two toxicity tests. Specifically, the effect of increasing calcium concentration (and hardness) on copper toxicity appears to be minimal. Also, there is fairly good agreement between the BLM and the two toxicity tests for test solutions containing elevated DOC, for which the LC50 is 3-to-5 times greater (less toxic) than the LC50 for the lower-DOC test water. This illustrates the protective effects of DOC on copper toxicity and demonstrates the ability of the BLM to predict these protective effects. In contrast, for test solutions with added iron there is a decrease in LC50 values (increase in toxicity) in results from the two C. dubia toxicity tests, and the agreement between BLM LC50 predictions and results from these toxicity tests is poor. The inability of the BLM to account for competitive iron binding to DOC or DOC fractionation may be a significant shortcoming of the BLM for predicting site-specific water-quality criteria in streams affected by iron-rich acidic drainage in mined and mineralized areas. Additional

Landscape geochemistry near mineralized areas of eastern Alaska: Chapter H in Recent U.S. Geological Survey studies in the Tintina Gold Province, Alaska, United States, and Yukon, Canada--results of a 5-year project

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Hydrogeochemical investigations in the Osgood mountains, north-central Nevada. Chapter B.

Field investigations performed in the Osgood Mountains during the summers of 1999 and 2000 were designed to test methods of combining geologic, hydrologic, and geochemical investigations. The goals were to develop a more thorough understanding of the movement of water through the study area and to understand the water-rock reactions that may occur along flow paths. The Osgood Mountains were chosen for study because they represent a well-defined geologic system, based on existing and new field data. New work in the area focused on gathering more data about fractures, faults, and joints and on collecting water samples to evaluate the role of geologic structures on hydrologic and geochemical properties of the ground-water/surface-water system. Chemical methods employed in the study included measuring traditional field parameters (e.g., pH, temperature, conductivity, dissolved oxygen) as well as Fe2+ and collecting a variety of samples that were preserved for later laboratory analysis. Hydrologic methods included closely spaced evaluations of substream hydraulic head to define ground-water discharge and recharge zones as well as some measurements of stream discharge. Geologic investigations focused on the locations and orientations of fractures and kinematic indicators of slip observable in outcrops.