British Columbia Mine Reclamation Symposia

Ecological risk assessment for a mine pit lake, Nevada, USA Sampson, Jennifer R.; Mellott, Ron S.; Pastorok, Robert A. 1996

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Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation ECOLOGICAL RISK ASSESSMENT FOR A MINE PIT LAKE, NEVADA, USA Jennifer R. Sampson Ron S. Mellott  Robert A. Pastorok, Ph.D. PTI Environmental Services 15375 SE 30th Place, Suite 250 Bellevue,WA 98007 ABSTRACT Closure of an open pit gold mine in central Nevada, USA, will result in cessation of dewatering at the mine and formation of a pit lake. The future pit lake will occur in a desert shrub community and have no surface water inflows or outflows. An ecological risk assessment far the pit lake was conducted as part of an environmental impact statement required for expansion of mine facilities. Because the pit lake does not yet exist, ecological risks were estimated from the results of predictive water quality models and measurement of chemical concentrations in the rock wall of the pit. The exposure of birds and mammals to individual metals through food and water ingestion was estimated on the basis of concentrations of metals in water and bioconcentration factors and through sediment ingestion was estimated from concentrations of metals in wall rock. Exposure estimates, which were expressed as daily rates of intake of individual metals, were compared to no-effects and lowest-effects doses reported in the literature for those metals. Results of the risk assessment demonstrated minimal risks to dabbling ducks from exposure to zinc and no risk to other wildlife from chemical exposures. INTRODUCTION Expansion of gold mining activities that may result in impacts to U.S. public resources such as wildlife or groundwater is subject to the requirements of an environmental impact statement (EIS). The purpose of preparing an EIS is to determine whether proposed activities will result in adverse impacts on associated fish, wildlife, and habitats in the vicinity of the proposed action and to determine the magnitude of those impacts. This paper documents the successful implementation of ecological risk assessment (ERA) to meet the requirements for permitting the expansion of a gold mine in Nevada. TID our knowledge, this is the first application of a predictive ERA to a mine pit lake. This experience demonstrates the value of ERA in characterizing potential ecological impacts and reducing uncertainties in the permitting process. The proposed action includes cessation of mining activities within a gold quarry and discontinuation of pit dewatering, resulting in the formation of a pit lake. Because the pit lacks surface water inflows and outflows and is located in an arid region where annual evaporation significantly exceeds precipitation, naturally occurring chemicals in the groundwater as well as chemicals brought into solution by the breakdown of wall rock will concentrate over time. To the extent that formation of a lake in an arid desert environment creates an attractive habitat for waterfowl and passerine birds, as well as a drinking water source for large mammals and raptors, 74 Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation increasing concentrations of metals may lead to relatively high exposures of wildlife to potential toxicants. The ERA was used to estimate exposures of representative species expected to use the pit lake (receptors) to metals in the pit lake and to compare predicted exposures to toxicity reference values (TRVs) for ecological receptors. Hydrological and water chemistry models were used to predict groundwater inflow rates and chemical concentrations, respectively. However, this paper presents only the results of those models as they relate to the ERA and is focused on the risk assessment approach, models, and results. Methods and assumptions of the hydrological models (HSI 1994) and the water quality models (PTI 1995a) are documented elsewhere. A more complete discussion of the ERA methods, assumption!!, and uncertainties is provided by PTI (1995b). STUDY SITE The pit lake is located in the Great Basin, within a subunit of the Basin and Range Physiographic Province (Ryser 1985). The rim of the mine pit is 6,500 ft above mean sea level. The vegetation community at the mine site is dominated by grass species, big sagebrush (Artemesia tridentata), and open stands of single-leaf pinyon pine (Pinus monophylld) and Utah juniper (Juniperus osteosperma) (Ryser 1985). The pit lake is expected to fill with water from underground sources and precipitation to a maximum depth of 325 ft by the end of 159 years, at which time the pit lake will be considered to have reached hydraulic equilibrium (HSI 1994; PTI 1995a). The lake surface is predicted to rise another 3 ft during the ensuing 170 years. Thus, the surface of the pit lake is predicted to rise at a rate of 8.8 ft/year during the first 20 years following closure of the mine, 2 ft/year for the following 56 years, and 0.3 ft/year for the subsequent 83 years (HSI 1994). At equilibrium, the surface of the pit lake is predicted to be 700-1,000 ft below the surrounding land surface (HSI 1994) and to encompass a surface area of approximately 155 acres. The initial rapid rise of water (8.8 ft/year or greater) arid variation in water level is likely to preclude development of significant shallow-water habitats and associated aquatic communities (i.e., rooted aquatic macrophytes and benthic macroinvertebrates) that would attract wildlife. As hydrologie conditions approach equilibrium, aquatic plant and invertebrate communities may become established along the perimeter of the pit lake. After 76 years, the shallowest submerged bench could create a shallow-water zone lake of approximately 9 acres around the pit, which could sustain rooted macrophytes and provide !habitat for aquatic invertebrates, shorebirds, and dabbling ducks. Small patches of vegetation may inhabit the lake perimeter at any point after mine closure. 75 Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation METHODS Ecological Risk Assessment ERA consists of a problem formulation phase (including description of the site and habitats, listing of chemicals of potential concern, identification of measurement and assessment endpoints, and selection of receptors), exposure assessment, effects assessment, and risk characterization (U.S. EPA 1992). Both a screening-level risk assessment (to identify the chemicals expected to occur in pit lake water that will be significantly below concentrations that are hazardous to wildlife) and a food-web exposure model were used in the ERA for the pit lake. The principal difference between the two approaches is that the screening-level risk assessment uses highly conservative assumptions and readily available screening values so that those metals posing no risk to wildlife can be identified and dismissed from further analysis with confidence. A food-web model incorporating more realistic exposure assumptions was used to evaluate metals predicted to occur at concentrations greater than screening values. Chemicals of Potential Concern The chemicals selected for evaluation in the risk assessment were those measured in the water from developed wells after the beginning of 1993. The analyte list corresponded to the Nevada Division of Environmental Protection (NDEP) Profile I analyte list used for mining water pollution control permits. Assessment and Measurement Endpoints The assessment endpoint for this risk assessment was the reproductive potential of the population of each receptor species. The indicator of effects was the reproductive toxicity of each chemical to each receptor species. Ingested doses, or TRVs, associated with reduced viability of embryos, reduced viability or survivorship of young, or reduced fecundity were the measurement endpoints for this evaluation. Selection of Receptors Modeling the exposure for all species that may use the pit lake as breeding or foraging habitat or for drinking is impractical and unnecessary. A subset of species expected to use the pit lake was selected to represent species protected by federal or state laws and species with societal value. Receptors also reflect all relevant exposure pathways, including ingestion of water, aquatic vegetation, aquatic invertebrates, and sediments. Exposures to wildlife could be elevated if fish were present in the pit lake because fish bioaccumulate some of the more toxic metals (e.g., mercury). It was assumed for this risk assessment that no fish would be present in the pit lake 76 Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation because an 8-ft security fence topped with barbed wire surrounded by a rock berm would be installed to prevent stocking of the pit lake with fish. Therefore, fish-eating wildlife were not included in the list of selected receptors. Screening-Level Risk Assessment Two sets of screening criteria were applied: one for mammals and one for birds. To screen the list of constituents for mammals, highest median concentrations of pit lake constituents predicted for each time period were compared to drinking water standards for the protection of human health. Drinking water standards are based on a 70-kg mammal (human) consuming 2 L/day every day for 70 years. Chemicals that are known to be carcinogenic are regulated to a risk level of 10-5. Human health drinking water standards represent a conservative benchmark for the protection of large mammals. To screen the list of constituents for birds, toxicological benchmarks were derived from the specific exposure parameters and no-observed-adverse-effects levels (NOAELw) for mallard ducks. Because mallards could consume both plants and insects from the pit lake, they are likely to be the avian receptor with the greatest exposure potential. Benchmark values for mallards were derived with the following equation:  It was assumed that mallards obtain 92 percent of their diet from plante (41 percent) and insecte (51 percent) inhabiting the pit lake (with the remaining fraction of the diet from upland sources) and that chemicals are 77 Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation absorbed as efficiently by wild mallards from wild foods and water as they are by laboratory animals given laboratory foods. Exposure Assessment The exposure assessment was based on the results of the pit lake water quality model (PTI 1995a) and concentrations of metals in wall rock, as well as assumptions concerning the behavior of receptors and their expected uses of the pit lake. Described below are the methods used to determine concentrations of metals in each medium and to calculate the daily dose to receptors of those metals that did not pass the screening criteria used in the food-web model. Exposure assumptions are based on a review of the literature and conversations with wildlife experts concerning the behavior and food requirements of each receptor species. Metal Concentrations in Water Water chemistry models (HSI 1994; PTI 1995a) were used to predict the concentrations of metals during the first 330 years following closure of the mine. Metals for which concentrations, were modeled were those on the NDEP Profile I analyte list detected in groundwater samples and those associated with mine activities. The 330-year postclosure period was subdivided into short-term (0-159 years) and long-term (160-33O years) modeling periods. Exposure estimates presented here were derived from the highest value of the median predicted concentration of each metal for 159 years and 330 years postclosure. The methods and assumptions used to predict pit lake water chemistry are described by PTI (1995a). Metal Concentrations in Sediment Average concentrations of aluminum, mercury, selenium, silver, and zinc in wall rock were used as estimates of concentrations of metals in sediment because it is probable that wall-rock erosion and bench decomposition will contribute the majority of sediments to the pit lake, and contributions from atmospheric deposition of dust will be negligible.   In addition, the estimated concentrations of metals in sediment derived from the water column (chemical precipitates and organic detritus) were within the range of concentrations observed in wall rock (PTI 1995b). Metal Concentrations in Biota Bioconcentration factors (BCFs) derived from the literature were used to predict the concentrations of each metal in aquatic invertebrates and plants. The predicted conœntration of a metal in pit lake water was multiplied by its 78 Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation BCF, as described in Equations 3 and 4, to provide an estimate of the concentration of the metal in the aquatic animal or plant. BCFs are reported in liters per kilogram (dry weight). Food-Web Exposure Model For those chemicals predicted to occur at concentrations greater than screening levels, the daily rate of ingestion of each chemical by individual receptors was estimated using more realistic exposure parameters incorporated into a food-web exposure model as follows:  For receptors expected to consume aquatic invertebrates and aquatic plants, C; values for these food sources were estimated by multiplying the expected concentration of the metal in water (Cp in milligrams per liter) by the BCF of the food organism (liters per kilogram of the food organism). The term Cplants in the food-web exposure model then becomes:  79Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation   CP x BCFinvertebrates (4) Absolute gastrointestinal absorption efficiency for a chemical varies depending on the form and the matrix in which a chemical occurs. Absorption of metals from laboratory foods is expected to be different than absorption of metals from wild foods or from sediments. The relative gastrointestinal absorption efficiency (A;) reflects the difference between absorption of metals from wild food or sediment and absorption of chemicals from laboratory foods. Site-specific data on the relative absorption efficiency of metals by the receptors consuming food from the pit lake are not available. On the basis of PTI (1994), ATSDR (1994), and Pascoe et al. (1994), bioavailability from dietary sources in the wild was assumed to be less than bioavailability in the laboratory because chemicals in wild foods may be more tightly bound to cellulose, protein, and other substances than the soluble form of a chemical spiked into laboratory food or water. The relative absorption efficiency of chemicals from both diet and soil in the field is assumed to be one-half (0.5) the absorption efficiency in the laboratory. Relative absorption efficiency from water is assumed to be 1 .0. Other key exposure assumptions made on the basis of natural history of receptors are summarized in Table 1. Effects Assessment TRVs for metals were derived from the toxicological literature. Both NOAELs and lowest-observed-adverse-effects levels (LOAELs) were used, depending on which values were available. TRVs reported in the literature were extrapolated to derive species-specific TRVs for each receptor species using the method described by Opresko et al. (1994). Species-specific TRVs (expressed as NOAELw or LOAELw) were either used to derive the toxicological benchmarks or used directly as a basis for comparison for calculating hazard quotients as described below. Effects of alkalinity, calcium carbonate, chloride, hydrogen ions, magnesium, potassium, sodium, sulfate, and total dissolved solids on mammals were assumed to be negligible, because it was assumed that mammals would 80 Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation  find saline water unpalatable and would avoid drinking it. To evaluate the effects of these constituents on birds, the total dissolved solids concentration was converted to conductivity and compared to no-effects levels (TRVs) in ducks reported by Mitcham and Wobeser (1988a,b). Risk Characterization Hazard quotients were used for the risk estimate in both the screening-level risk assessment and the more detailed food-web model and risk assessment. In general, a hazard quotient is calculated as the expected environmental exposure divided by the TRV (e.g., NOAELw or LOAELw), or the benchmark value, and serves as the basis for the risk characterization. Thus, the hazard quotient is an expression of the factor by which the estimated exposure exceeds some exposure value associated with an adverse effect (benchmark or TRV). Interpretation of the hazard quotient depends heavily on the assumptions used to derive the exposure estimate and the lexicological endpoint represented by the NOAEL or LOAEL value. For the screening-level risk assessment, hazard quotients were calculated as:  TABLE 1.   VALUES FOR BODY WEIGHT AND FOOD, WATER, AND SEDIMENT INGESTION RATES OF RECEPTORS81Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation   RESULTS Selection of Receptors The receptors selected for the risk assessment were killdeer (Charadrius vociferus), cliff swallow (Hirundo pyrrhonotd), mallard (Anas platyrhynchos), golden eagle (Aquila chrysaetos), mule deer (Odocoileus hemionus), and bighorn sheep (Ovis canadensis). These receptors represent the diverse biota expected to use the pit lake and a variety of exposure pathways. Exposure Assessment Exposure assumptions for each receptor are summarized in Table 1. The predicted concentration of each metal in water in both the short-term and the long-term scenarios are reported by PTI (1995a) and summarized in Table 2. Estimates of sediment chemistry are also presented in Table 2 (PTI 1995b). BCFs were obtained from the literature and are summarized in Table 3. The basis for selection of BCF values used in this risk assessment is provided in PTI (1995b). Résulte of the food-web model were incorporated directly into calculation of the hazard quotients presented in the risk characterization. 82 Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation TABLE 2.   MEDIAN CONCENTRATIONS OF CHEMICALS OF POTENTIAL CONCERN IN WATER AND SEDIMENT PREDICTED FOR THE PIT LAKE  Effects Assessment The TRVs that were used for calculation of species-specific NOAELw and LOAELw values are presented in Table 4. NOAELw and LOAELw values are not presented but are incorporated directly into calculation of benchmarks (Cwater) or compared directly to doses estimated using the food-web model. 83 Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation  Risk Characterization  Screening-Level Risk Assessment Results of the screening-level assessment (Table 5) indicate that, during the entire 330-year modeling period, antimony, cadmium, chloride, chromium, copper, iron, lead, manganese., selenium, silver, thallium, and zinc are unlikely to affect mammals adversely and that arsenic, copper, and lead are unlikely to adversely affect birds using the pit lake. The cumulative concentration of alkalinity, calcium, carbonate, chloride (birds), hydrogen ions, magnesium, potassium, sodium, and sulfate is expressed as conductivity, which is below levels that cause adverse effects on juvenile ducks in laboratory experiments (Mitcham and Wobeser 1988a,b). On the basis of the results of the screening-level risk assessment, the risk of exposure of mammals to aluminum, arsenic, fluoride, mercury, and nickel was evaluated using a food-web exposure model and hazard quotient. In addition, risk to all birds from exposure to mercury, selenium, and zinc and risk to killdeer and cliff swallow from exposure to aluminum and silver were evaluated using the food-web exposure model and hazard quotient. Food-Web Exposure Model The results of the food-web exposure modeling and comparison to NOAELw and LOAELw values using hazard quotients (Table 6) indicate that if water ingestion is the only exposure route, hazard quotients for all receptors 84 TABLE 3.   BIOCONCEEIMTRATIOIM FACTORS USED TO ESTIMATE CHEMICAL CONCENTRATIONS IN AQUATIC FOODS OF WILDLIFE SPECIES Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation  and for all chemicals are less than 1.0 in both the short-term and long-terra modeling periods. Therefore, because mule deer, bighorn sheep, and golden eagle are expected to only drink water from the pit lake, these species are not at risk from chemical constituents of the pit lake. Any mallard ducks, cliff swallows, or killdeer that do not obtain food from the pit lake also are not at risk. Assuming that killdeer, cliff swallows, and mallards obtain their food from the pit lake, risk to killdeer and cliff swallows from exposure to aluminum, mercury, selenium, or silver is negligible because predicted exposures are below NOAELw values (hazard quotient less than 1.0). Exposure of mallards to aluminum and silver could not 85 TABLE 4.  TOXICITY REFERENCE VALUES FOR CHEMICALS Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation Note:   -- - data gap; analyte could not be screened in the risk assess- ment NA        - not analyzed; analyte not expected to affect wildlife NOAEL - no-observed-adverse-effects level S - incorporated calculation of total dissolved solids (TDS) for comparison with the toxicity reference value for TDS a Hazard quotient equals highest median concentration predicted for any time period   by  water  quality  model  divided   by  human  health  drinking   water standard. b Hazard quotient equals highest median concentration predicted for any time period divided by the NOAEL-based toxicological benchmark for mallards. 86  TABLE 5.   RESULTS OF THE SCREENING-LEVEL ASSESSMENT Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation TABLE 6.  RESULTS OF THE FOOD-WEB EXPOSURE MODEL AIMD RISK CHARACTERIZATION  Source:   PTI(1995b) Note:       NA not applicable a Hazard quotient is based on wildlife lowest-observed-adverse-effects level. b Food, water, and sediment. c Hazard quotient in parentheses is based on wildlife lowest-observed-adverse-effects level. 87 Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation be evaluated because water-to-plant BCFs were not available for these chemicals. In addition, mallard popula-tions are not at risk from exposure to mercury. The exposure of mallards to selenium in both the short-term and the long-term scenarios exceeds the NOAELw but does not exceed the LOAELw, indicating that risk to mallards from exposure to selenium is minimal. Exposure of all bird receptors to zinc in the long-term scenario is greater than NOAELw values, but exposures of killdeer and cliff swallows are less than LOAELw values, indicating that there is no risk to killdeer and cliff swal-lows from exposure to zinc. Exposure of mallards to zinc could exceed the LOAELw value in the short-term scenario by a factor of 1.2 and in the long-term scenario by a factor of 2.4. These estimates are driven by a rela-tively high value for the water-to-plant BCF for zinc (Table 3). Uncertainty analysis indicates that water-to-plant BCFs for zinc range from 10 to 4,875 L/kg. When calculated with the median BCF (440 L/kg), the zinc hazard quotient for mallards is 0.35 in the short term and 0.69 in the long term. Therefore, the uncertainty associated with the risk estimate for mallards is greater than an order of magnitude, and the hazard quotient of 2.4 approxi-mates the upper bound risk estimate. The risk of exposure of mammals to strontium and of birds to antimony, cadmium, chromium, fluoride, iron, manganese, nickel, strontium, and thallium could not be analyzed because of data gaps (Table 4). In addition, exposure of mallards to aluminum and silver could not be evaluated because water-to-plant BCFs were not avail-able for these chemicals. DISCUSSION The results of this ERA indicate negligible risk to wildlife populations from aluminum, antimony (mammals only), arsenic, copper, fluoride (mammals only), lead, manganese, mercury, nickel (mammals only), selenium, silver, zinc (mammals only), or total dissolved solids. Results of the food-web exposure model indicate that the average daily intake of zinc by mallards nesting and feeding at the pit lake for the long-term modeling period could exceed both the NOAELw and LOAELw values. Sources of uncertainty in this ERA include 1) the assumptions that form the basis for predictions of pit lake chemical concentrations, 2) data gaps for exposure variables and NOAELw or LOAELw values, 3) the extent to which shallow water zones and shorelines will develop into vegetated aquatic habitat, 4) the extent to which pit lake habitats will be used by wildlife, 5) vari-ability in chemical toxicity related to species differences and chemical interactions (e.g., synergistic and antago-nistic relationships between chemicals), and 6) variability in BCFs related to species differences and site-specific environmental factors. To compensate for uncertainties and avoid underestimating risk, wildlife risk models were 88 Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation developed using conservative assumptions. As a result, the predicted exposures are probably higher than will actually occur. Although data gaps remain, the results of this ERA indicate that pit lake water and sediments will not pose a significant population-level risk to wildlife ibr up to 330 years after mine closure. REFERENCES ATSDR. 1994. Toxicological profile for mercury. Prepared for U.S. Department of Health and Human Services, Public Health Service. Agency for Toxic Substances and Disease Registry, Atlanta, GA. Ambrose, A.M., P.S. Larson, IF. Borzelleca, and G.R. Hennigar, Jr. 1976. Long-term toxicologie assessment of nickel in rats and dogs. J. Food Sci. Tech. 13:181-187. Aulerich, RJ., R.K. Ringer, M.R. Bleavins, and A. Napolitano. 1982. Effects of supplemental dietary copper on growth, reproductive performance and kit survival of standard dark mink and the acute toxicity of copper to mink. J. Animal Sci. 55:337-343. Carrière, D., K. Fischer, D. Peakell, and P. Angehrn. 1986. 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Manage. 53:418-428. Hermayer, R.L., P.E. Stake, and R.L. Shippe. 1977. Evaluation of dietary zinc, cadmium, tin, lead, bis-muth and arsenic toxicity in hens. Poult. Sci. 56:1721-1722. Hill, C.H., and G. Matrone. 1970. Chemical parameters in the study of in vivo and in vitro interactions of transition elements. Federation Proceedings 29(4)1474-1481. HSI. 1994. Groundwater flow model results, Round Mountain Mine, Environmental Impact Statements, Round Mountain, Nevada. Prepared by Hydro-Search, Inc., Reno, NV. Prepared for Round Mountain Gold Corporation, Round Mountain, NV. 89 Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation Krapu, G. 1995. Personal communication (telephone conversation with J. Sampson, PTI Environmental Services, Bellevue, WA, on June 28, 1995, regarding the diet of mallards). U.S. Fish and Wildlife Service, Jamestown, ND. Lawson, B., and R. Johnson. 1982. Mountain sheep. In: Wild Mammals of North America. J.A. Chap-man and G.A. Feldhamer (eds). John Hopkins University Press, Baltimore, MD. Lee, C.K., K.S. Low, and N.S. Hew.  1991. Accumulation of arsenic by aquatic plants   Sci Tot Environ 103:215-227. Mackie, R.J., K.L. Hamlin, and D.F. Pac. 1982. Mule deer. In: Wild Mammals of North America. J.A. Chapman and G.A. Feldhamer (eds). John Hopkins University Press, Baltimore, MD. Mehring, A.L., Jr., J.H. Brumbaugh, AJ. Sutherland, and H.W. Titus. 1960. The tolerance of growing chickens for dietary copper. Poult. Sci. 39:713-719. Mitcham, S.A., and G. Wobeser. 1988a. Toxic effects of natural saline waters on mallard ducklings. J. Wild. Dis. 24(1)45-50. Mitcham, S.A., and G. Wobeser. 1988b. Effects of sodium and magnesium sulfate in drinking water on mallard ducklings. J. Wild. Dis. 24(1)30-44. Ondreicka, R., E. Ginter, and J. Kortus. 1966. Chronic toxicity of aluminum in rats and mice and its effects on phosphorus metabolism. Brit. J. Indust. Med. 23:305-313. Opresko, D.M., B.E. Sample, and G.W. Suter II. 1994. Toxicological benchmarks for wildlife: 1994 revision. ES/ER/TM-86/R1. Prepared for the U.S. Department of Energy. Oak Ridge National Labora-tory, Oak Ridge, TN. Nehring, R.B. 1976. Aquatic insects as biological monitors of heavy metal pollution. Bull. Environ. Contam. Toxicol. 15(2)147-154. Pascoe, G.A., RJ. Blanchet, and G. Linder. 1994. Bioavailability of metals and arsenic to small mam-mals at a mining waste-contaminated wetland. Arch. Environ. Contam. Toxicol. 27:44-50. Pattee, O.H. 1984. Eggshell thickness and reproduction in American kestrels exposed to chronic dietary lead. Arch. Environ. Contam. Toxicol. 13:29-34. PTI. 1994. National Zinc Site remedial investigation and feasibility study, Volume I, remedial investiga-tion report. PTI Environmental Services, Bellevue, WA. PTI. 1995a. Predicted water quality in the Round Mountain Gold Company pit lake - Nye County, Nevada. Prepared for Round Mountain Gold Corporation, Round Mountain, NV. PTI Environmental Services, Boulder, CO. PTI. 1995b. Assessment of risk to wildlife from predicted chemical concentrations at the Round Mountain Gold Corporation pit lake, Nevada. Prepared for Round Mountain Gold Corporation, Round Mountain, NV. PTI Environmental Services, Bellevue, WA. 90 Proceedings of the 20th Annual British Columbia Mine Reclamation Symposium  in Kamloops, BC, 1996. The Technical and Research Committee on Reclamation Ryser, F.A., Jr.  1985. Birds of the Great Basin: a natural history. University of Nevada Press, Reno, NV. Schlicker, S.A., and D.H. Cox. 1968. Maternal dietary zinc, and development and zinc, iron, and copper content of the rat fetus. J. Nutr. 95:287-294. Schroeder, H.A., and M. Mitchener. 1971. Toxic effects of trace elements on the reproduction of mice and rats. Arch. Environ. Health 23:102-106. Schuler, C.A., R.G. Anthony, and H.M. Oldendorf. 1990. Selenium in wetlands and waterfowl foods at Kesterson Reservoir, California, 1984. Arch. Environ. Contain. Toxicol. 19:845-853. Sinha, S., and P. Chandra. 1990. Removal of Cu and Cd from water by Bacopa monnieri L. Water Air Soil Pollut. 51:271-276. Suter, G.W.  1993. Ecological risk assessment. Lewis Publishers, Boca Raton, FL. U.S. EPA. 1980. Ambient water quality criteria for arsenic. EPA 440/5-80-021. U.S. Environmental Protection Agency, Office of Water Regulations and Standards, Criteria and Standards Division, Washing-ton, DC. U.S. EPA. 1992. Framework for ecological risk assessment. EPA/63O/R-92/001. U.S. Environmental Protection Agency, Risk Assessment Forum. U.S. EPA. 1993. Wildlife exposure factors handbook. Volume I. EPA/600/R-93/187a. U.S. Environ-mental Protection Agency, Office of Water, Office of Science and Technology, Washington, DC. Verschuuren, H.G., R. Kroes, E.M. Den Tonkelaar, J.M. Berkvens, P.W. Helleman, A.G. Rauws, P.L. Schuller, and GJ. Van Esch. 1976. Toxicity of methylmercury chloride in rats. II. Reproductive study. Toxicol. 6:97-106. 91 

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