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PUBLIC HEALTH ASSESSMENT

STIBNITE/YELLOW PINE MINING AREA
STIBNITE, VALLEY COUNTY, IDAHO


SUMMARY

The Stibnite Mine Area (Stibnite) engaged in active mining operations from the early 1900's until the late 1990's. Stibnite is located along the East Fork of the South Fork of the Salmon River, 14 miles southeast of the town of Yellow Pine, Valley County, Idaho. The mine was a major producer of antimony and gold. Past mining activities have deposited metals, spent and neutralized ore, waste rock, and mine tailings over approximately fifty percent of the 3,000 acre site. The Bureau of Environmental Health and Safety (BEHS), Division of Health, Idaho Department of Health and Welfare reviewed available environmental data, health information, and community health concerns for the development of this public health assessment. Stibnite/Yellow Pine Mining Area (Stibnite) site was proposed to U.S. Environmental Protection Agency's (EPA) National Priority List (NPL) on September 13, 2001. This document fulfills ATSDR Congressional mandate for preparing a public health assessment within one year of EPA proposing a site to the NPL. The BEHS prepared this public health assessment under a cooperative agreement with the federal Agency for Toxic Substances and Disease Registry (ATSDR).

Conclusions

  • The completed exposure pathways identified include: surface soil, surface water, airborne particulates and sediments. The most important exposure pathway is the ingestion of surface soil and inhalation of airborne particulates. As there are no air contaminant concentrations available, and to be protective of public health, BEHS assumes that the exposure dose from inhalation is the same as from ingestion of surface soil. Consumption of fish is a potential exposure pathway, while subsurface water and ground water are eliminated exposure pathways.
  • There is no information available about former mine workers, thus BEHS is unable to evaluate their past exposures and the public health implications of these exposures.
  • It is unlikely that the contaminants at the Stibnite site will result in any adverse public health effects for the reclamation workers and recreational users, since the estimated exposure doses are either below the corresponding health guideline values, or below the corresponding lowest NOAELs (or LOAELs) in all the related studies. The predicted increased risk of cancer from arsenic is so low as to be negligible to the reclamation workers and recreational users.
  • According to ATSDR's Interim Public Health Hazard Categories, the exposure pathways related to surface soil and sediment, airborne particulates, surface waters, and fish are categorized as no apparent public health hazard (Appendix B). However, the public health hazard posed by the consumption of biota (other than fish) cannot be evaluated at this time due to a lack of data and information, which is categorized as an indeterminate public health hazard.

Recommendations

  • As a precaution, site access should be restricted by placing obvious "no trespassing" signs to prevent the public from entering the site, especially in the hotspot areas.
  • BEHS should provide health education materials to the populations that use the site about potential health impacts of the Stibnite site.
  • The reclamation workers should be cautious about ingestion of surface soil and surface water.
  • Hot spot remediation is prudent even though BEHS does not believe that exposures will result in any adverse public health effects to the recreational users and reclamation workers
  • Biota (other than fish) samples should be collected and analyzed for potential uptake of metals from site soils and surface water.

Public Health Action Plan

  • BEHS will conduct health education activities to inform Yellow Pine residents of the status of the site. Recommendations against using the site for recreation will also be made.
  • BEHS will assist the United States Forest Service and EPA with their community involvement plan as necessary.
  • BEHS forwarded this document to HECLA and brought attention to the third recommendation, referring to their site workers.
  • BEHS will request that the regulatory agencies involved with this site implement the fifth recommendation. If the agencies are unable to fulfill this request, BEHS and ATSDR will explore the feasibility of conducting an exposure investigation with regard to site biota.
  • BEHS will review additional environmental sampling data as it becomes available.
  • IDEQ is negotiating institutional controls with the current site owners to prevent future development of the site.
  • IDEQ is negotiating with the site owners about how to prevent public exposure to the onsite contamination. Possible actions include site access restriction, posting warning signs, and site reclamation. Reclamation activities will focus on securing tailings piles and other contamination in such a way that the public and eco-receptors (biota) can utilize the area without the threat of exposure.
  • IDEQ will require that the mill building containing mineral extraction equipment and chemicals be removed and properly disposed of along with process chemicals.
  • IDEQ will arrange to have damaged buildings on site removed if they interfere with site reclamation or pose a significant threat to site safety.

1. PURPOSE AND HEALTH ISSUES

The Bureau of Environmental Health and Safety (BEHS), Division of Health, Idaho Department of Health and Welfare has a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR) to conduct public health assessments and consultations for hazardous waste sites in Idaho. BEHS completed this public health assessment under this cooperative agreement.

A public health assessment is a tool used to determine if and what kind of activities are needed to protect the health of a community residing/working near a hazardous waste site, and to determine the need for follow-up health activities (e.g., health study). To achieve this goal, this assessment contains three types of evaluations: (1) the identification of pathways of exposure to site contaminants and an evaluation of their public health implications; (2) a summary of relevant and available health outcome data (e.g., cancer registry data); and (3) evaluations of specific community health concerns about the site.

Stibnite/Yellow Pine Mining Area (Stibnite) site was proposed to the U.S. Environmental Protection Agency's (EPA) National Priority List (NPL) on September 13, 2001. This document fulfills ATSDR Congressional mandate for preparing a public health assessment within one year of EPA proposing a site to the NPL.


2. BACKGROUND

2.1 Site Description

The Stibnite/Yellow Pine Mining Area (Stibnite) site is located in Valley County, Idaho approximately 14 miles southeast of the town of Yellow Pine on Forest Road 50412 (see site location and maps in Appendix A). No permanent or year-round residents reside onsite. Seasonal workers and recreational users are the only people observed coming into contact with the site (Schuld 2002). Hunting, fishing, dirt bike or ATV riding, and camping are the main recreational activities conducted at the site.

Stibnite is located within the Payette National Forest on a mixture of National Forest Service and private lands. The site is defined as all the waste sources and areas between the sources resulting from mining activity along Meadow Creek and the East Fork of the South Fork of the Salmon River (EFSFSR) to the old Yellow Pine Pit, now referred to as the Glory Hole. Situated in a valley, Stibnite is surrounded by steep, forested mountains and various tributaries, including Meadow Creek and Sugar Creek, which drain into the EFSFSR (USFS 1993). The site encompasses over 3,000 acres, although the actual areas of contamination exposure are much smaller, ranging from less than 1 acre to 119 acres. Approximately 50% of the site has either exposed tailings or is underlain by tailing which are susceptible to weathering and re-exposure (Schuld 2002). Annual precipitation averages approximately 31 inches. Most of the precipitation falls as snow from October through April. The predominant geology of the area is faulted granitic bedrock (specifically granodiorite) which contains oxide and sulfide ores. These ores are rich in gold, silver, mercury, antimony, and tungsten (URS 2000).

The majority of the mining and processing at the Stibnite Mine took place on patented claims on private lands within the Payette National Forest. Site mining activities generated numerous waste source areas along Meadow Creek and the EFSFSR. Changes in topography, stream channels, water quality, and habitat resulted from past site-related activities (URS 2000).

2.2 Site History

Gold, silver, copper, lead, antimony, and tungsten have been mined from Stibnite since the early 1900's. The first recorded claims were from 1914, staked by Albert Hennessy. The United Mercury Mining Company purchased the claims from Hennessy. The F. W. Bradley Mining Company obtained the claims in 1927. The Bradley Mining Company began mining and milling gold in the 1930's. Two years prior to the United State's involvement in World War II, an act of Congress listed antimony and tungsten as strategic metals essential to national defense. Bradley Mining Company turned Stibnite into a major producer of antimony and tungsten from 1941 through 1945. During this time period, the town of Stibnite was located onsite and had a population of 1,500 with a staffed hospital and a recreation center (USFS 1993).

According to the US Forest Service (USFS) 1993 Preliminary Assessment / Site Investigation, the Bradley Mining Company originally mined underground but switched to open pit mining in 1943. In 1948, the Bradley Mining Company constructed and operated a smelter to process low grade gold and gold-antimony ore concentrates. The town of Stibnite immediately bordered the smelter area to the south and east (Schuld 2002). Tailings were stored at the south end of Meadow Creek and waste rock was placed along the banks of the EFSFSR downstream from the Glory Hole. The tailings along Meadow Creek averaged from 20 to 50 feet deep, 1,200 to 1,500 feet wide, and 2,200 feet long. As tailings were deposited along Meadow Creek, it became necessary to divert the creek. This diversion led to the formation of a pond behind the tailing impoundment as the seeps and springs continued to discharge water. A drainage culvert was constructed to drain the water and discharge it back into Meadow Creek. A dam was constructed on the East Fork of Meadow Creek (now called Blowout Creek) in order to supply hydroelectric power for milling operations. The dam failed in 1965 depositing large volumes of tailings into Meadow Creek, the EFSFSR, and the Glory Hole. The mine was closed in 1952 due to problems with the smelter and the collapse of the antimony market. By 1955, the processing plant was dismantled and most of the houses from the town of Stibnite were moved. The Meadow Creek diversions eventually failed allowing the stream to flow over and through the tailings. An estimated 10,000 cubic yards of tailing was eroded into the EFSFSR from 1952 to 1979.

In 1985, the Idaho Hazardous Materials Bureau conducted a Preliminary Assessment (PA) and submitted the results to the EPA. The site was assigned a Comprehensive Emergency Response Cleanup and Liability Act (CERCLA) identification number but did not score high enough to be included on the NPL. The Bradley tailings, spent ore piles, waste rock, old mining process chemicals (old Bradley mill), and the chlorine and cyanide processing plant were all listed in the PA as potential health threats. A site investigation was recommended, but not completed.

From 1970 to 1991, Stibnite claims were optioned or transferred numerous times. Companies that owned the claims at one time include: the Ranchers Exploration and Development Corporation, Canadian Superior Mining (U.S.) Ltd. (a.k.a. Superior Mining Company) which was purchased by Mobil Oil Corporation, Pioneer Metals, Pegasus Gold, Inc., and the Stibnite Mine Inc. (SMI). Pioneer Metals deposited neutralized ore with residual cyanide in it directly into Meadow Creek. They were issued a Notice of Violation by the Idaho Department of Environmental Quality (IDEQ) in 1990 for cyanide concentrations in Meadow Creek over the acute water quality standard. Detectable levels of cyanide were present in Meadow Creek for several years after.

Canadian Superior Mining started a full-scale cyanide-heap leach operation at Stibnite in 1982. Hecla Mining Corporation obtained the lease on the Bradley claims in 1988 and started an open pit mine and one-time heap leach. Hecla mined and processed low-grade oxide ore adjacent to the SMI operation. Hecla processed the remaining available oxide ore by the end of the 1991 mining season.

The gold mining operations from 1982 to 1998 took place in the West End Pit in the Meadow Creek Valley. During this period, neutralized ore from the leach pads was used to cover the Bradley tailings in upper Meadow Creek. Waste rock and neutralized ore was also used to cover other historic mining areas and tailings in the Meadow Creek Valley.

In 1991, the USFS discovered a release of arsenic. The release was documented through an analysis of steelhead trout taken from the EFSFSR below Sugar Creek. The trout tissue contained 6.38 parts per million (ppm) of arsenic. In 1993, the USFS conducted a preliminary assessment/site investigation (PA/SI) for the Stibnite site. Samples collected from the Bradley tailings and neutralized ore piles, waste piles in lower Meadow Creek Valley, stream sediments, Meadow Creek, and the EFSFSR indicated the presence of elevated concentrations of antimony, arsenic, cadmium, copper, lead, and mercury.

In 1993, SMI, under a consent order from the EPA, submitted a site investigation and evaluation report to IDEQ which documented the fact that the process ponds and on-off heap leach pads were leaking cyanide and chlorine into site soils and groundwater. The report also documented a release of diesel fuel into the site soils and groundwater. Total petroleum hydrocarbons were detected at levels in excess of EPA limits. Benzene, ethyl benzene, toluene, and total xylenes were also detected in the groundwater.

In 1995, SMI, under an Administrative Order of Consent (AOC) from the EPA, began further mitigation of environmental impact from the Bradley tailing pile in upper Meadow Creek Valley. The AOC was terminated by EPA in 1997 before the mitigation was complete. In 1998, Mobil entered into an AOC with the EPA to complete the cleanup left unfinished by SMI. Mobil was also required to reclamate and revegetate the Bradley tailing pile and reduce contaminant loads in Meadow Creek (URS 2000).

From 1997 through 1999, SMI, Hecla, and Mobil performed a Site Characterization Risk Evaluation at Stibnite. Surface water, ground water, seeps, springs, soil, sediment, and fish tissue were sampled and analyzed. Analytical results indicated the presence of elevated concentrations of antimony, arsenic, copper, cyanide, lead, and mercury in surface waters, ground water, tailings, neutralized ore, waste rock, smelter stack ash, process ponds, stream sediments, and fish. The Site Characterization and Risk Evaluation Reports were submitted to IDEQ in 2000. Stibnite was proposed to the NPL on September 13, 2001. Currently, the site is in the process of closure and is no longer actively mined (Schuld 2002).

2.3 Demographics

According to the 2000 US Census, the population of Yellow Pine, 14 miles away from the site, is 40 people. The site itself has no permanent residents. Hecla maintains a seasonal workforce of approximately six to eight people at Stibnite for approximately five months during late Spring through early Fall.

2.4 Site Visit

Representatives of BEHS visited the Stibnite Mine on July 10, 2002 to evaluate the site exposure pathways. IDEQ and the USFS representatives were on hand to assist BEHS with the site visit. The site visit was documented with digital photographs and field notes. BEHS directly observed evidence of recreational use (fire pit) in the Glory Hole area as well as game tracks in the former poison pond area and Bradley tailing piles. The capped and revegetated areas show little or no evidence of disturbance or erosion. The rest of the site contains vast tracts of disturbed soil and exposed tailings and neutralized ore piles. A significant amount of erosion was observed in areas that have not been capped or revegetated.


3. ENVIRONMENTAL CONTAMINATION AND OTHER HAZARDS

An essential part of every public health assessment is to review environmental contaminants on the site. In this section, BEHS has listed the contaminants of concern (Appendix C). BEHS evaluates these contaminants in the subsequent sections of the public health assessment to determine whether exposure to them has any public health significance. The results from environmental testing at Stibnite are summarized for each different environmental media (e.g. groundwater, surface water, soil, air, etc.).

In evaluating the contaminant concentrations in different environmental media, health-based comparison values (CVs) (Appendix C, Table C-1) are used as screening values to determine which chemicals to examine more closely. Media specific CVs, as developed by ATSDR, incorporate assumptions of daily exposure to specific chemicals. These assumptions include a standard amount of air, water, and soil that someone may inhale or ingest each day. CVs are established at concentrations below which no known or anticipated adverse human health effects are expected to occur. Different CVs are developed for cancer and non-cancer health effects. Non-cancerous levels are based on valid toxicological and epidemiological studies for a chemical. The non-cancerous levels include appropriate safety factors to account for human variability, extrapolating human studies from animal studies, etc. They also include the assumption that small children (22 pounds) and adults are exposed every day. Cancer levels are the media concentrations at which there could be a one in a million excess cancer risk for an adult eating contaminated soil or drinking contaminated water every day for 70 years. If more than one CV exists for a chemical (cancerous effect or non-cancerous level), the smaller value is always used for screening to be more conservative or protective. Exceeding a CV does not mean that health effects will occur, just that more evaluation is needed.

For non-cancer toxicity, BEHS typically uses Environmental Media Evaluation Guides (EMEGs) derived from ATSDR's Minimal Risk Levels (MRLs) or the Reference Dose Media Evaluation Guides (RMEG) derived from EPA's References Doses (RfDs). MRLs and RfDs are estimates of daily human exposure to a contaminant that is unlikely to cause adverse non-cancer health effects over a lifetime. Cancer Risk Evaluation Guides (CREGs) are risk comparison values based on EPA's chemical-specific cancer slope factors and an estimated excess lifetime cancer risk of one in one million.

In addition to the health-based comparison values, BEHS also references other standards and regulations when health-based comparison values are not available or when other standards are lower than the health-based comparison values (to be conservative or protective). EPA's Maximum Contaminant Level (MCL) is the highest level of a contaminant that is allowed in drinking water. MCLs are enforceable standards and they are set as close to the Maximum Contaminant Level Goal (MCLG) as feasible. MCLG is the level of contaminant in drinking water below which there is no known or expected risk to health. MCLGs are non-enforceable public health goals. The Lifetime Health Advisories for Drinking Water (LTHAs) are lifetime exposure levels for drinking water at which adverse, noncarcinogenic health effects would not be expected to occur. EPA also recommends secondary standards that are non-enforceable guidelines regulating contaminants that may cause cosmetic or aesthetic effects (e.g., smell, taste, and color) in drinking water. The secondary standards are not health-based. Sometimes secondary standards are 10 to 100 times lower than levels that would induce health effects. The lowest of all comparison values was used to identify compounds for further evaluation (Appendix C, Table C-1).

The public health implications of exposures to selected contaminants are evaluated in detail in the discussion section of this document. With this in mind, the following summary of environmental data highlights the chemicals that have been found on the site at levels above the comparison values, called the contaminants of concern. The sampling location identification numbers referenced in this public health assessment are the same as the Stibnite Area Risk Evaluation Report (URS 2000). The details about the selection of contaminants of concerns are summarized in Appendix C.

3.1 Soil

Surface soil samples were collected during the 1997 and 1999 site characterization activities. During the 1997 Site Characterization, 21 reference soil samples were collected from mineralized and non-mineralized areas outside the zone of influence of mining activities. In 1997, 52 soil samples were collected from areas known to be impacted by mining activities. In 1999, 46 additional samples were collected from the Bradley Waste Rock Dumps and the wetlands.

The following chemicals were detected in the analyzed samples: aluminum, antimony, arsenic, cadmium, chromium, copper, cyanide, lead, manganese, mercury, nickel, selenium, silver, and zinc. Of all the chemicals detected in the analyzed soil samples, only concentrations of antimony and arsenic were consistently elevated relative to the reference samples. Lead concentrations were elevated in samples collected from the upgradient wetland and mercury concentrations were elevated in samples collected from the smelter stack area. The soil sample results indicated that there are areas (Meadow Creek exposure areas) of moderately elevated concentrations of metals and other areas (Bradley waste rock dumps and hot spots) with significantly elevated concentrations of metals relative to the reference sample results.

Maximum concentrations of arsenic detected in soil samples collected from the Meadow Creek exposure areas ranged from 24.4 milligrams per kilogram (mg/kg) to 1,620 mg/kg. Maximum concentrations of arsenic detected in soil samples collected from the Bradley waste rock dump and other hot spots ranged from 983 mg/kg to 5,630 mg/kg. Maximum concentrations of antimony detected in soil samples collected from the Meadow Creek exposure areas ranged from 133 mg/kg to 1,550 mg/kg. Maximum concentrations of antimony detected in soil samples collected from the Bradley waste rock dump and other hot spots ranged from 292 mg/kg to 16,400 mg/kg.

The maximum concentration of lead detected in soils collected from the upgradient wetland was 754 mg/kg. In all other areas, the maximum concentrations or reasonable maximum exposure concentrations of lead detected in soil samples was less than health-based comparison values. The maximum concentration of mercury detected in soils collected from the smelter stack area was 471 mg/kg. Table C-2 and C-3, located in Appendix C, contain the maximum and reasonable maximum exposure concentrations for metals detected in soil samples collected from the site.

3.2 Surface Water and Sediment

Three surface water sampling events were conducted in 1997 and four additional sampling events were conducted in 1999. The following chemicals were detected in samples collected from site surface waters: aluminum, antimony, arsenic, copper, cyanide, lead, manganese, mercury, nickel, silver, and zinc. Background samples were collected from site surface waters in areas not impacted by mining operations. Only antimony, arsenic, and manganese were detected in concentrations above health-based comparison values.

Maximum concentrations of antimony detected in site surface water samples ranged from 0.0083 milligrams per liter (mg/L) to 0.281 mg/L. Maximum concentrations of arsenic detected in site surface water samples ranged from 0.012 mg/L to 0.535 mg/L. The maximum concentration of manganese detected in surface water collected from the keyway wetland was 0.785 mg/L. The Keyway wetland is the only area where detected concentrations of manganese in surface water exceeded health-based comparison values. Table C-4, located in Appendix C contains the maximum and reasonable maximum exposure concentrations for metals detected in surface water samples collected from the site.

3.3 Air and Dust

During past mining operations, crushing rock and hauling ore would likely have contributed to the creation of airborne particles on the site. Also, smelter stack emissions would have released contamination into the air. No environmental air samples have been collected at the site to date.

3.4 Biota

Two different sampling events were conducted at the site in 1997 and 1999 to collect fish for chemical analysis. Concentrations of antimony detected in whole body fish samples ranged from 0.07 micrograms per gram (g/g) to 0.42 g/g. Concentrations of arsenic detected in whole body fish samples ranged from 0.65 g/g to 3.30 g/g (Appendix C, Table C-5). Game and plant samples from the Stibnite site area have not been collected and analyzed for metals concentrations.

3.5 Groundwater

Yellow Pine residents use either private wells or the public water system, which is a surface water intake, as their drinking water source. The nearest active wells are located approximately 15 miles from the site. Groundwater quality has been impacted in the Meadow Creek Valley where the Bradley tailings piles are saturated or seasonally interface with groundwater (URS 2000). Detected concentrations of arsenic and antimony in samples collected from groundwater monitoring wells in this area ranged from 2 micrograms per liter (g/L) to 3,070 g/L for antimony and 3 g/L to 13,800 g/L for arsenic. These detections were elevated relative to reference samples collected outside the mining area.

3.6 Other Concerns

The mill building, while locked, poses a potential hazard to trespassers. Process chemicals, including cyanide, and carbon canisters are still present in the building. The outside of the mill building has been spray painted with warnings indicating the presence of poison inside. Multiple wooden buildings exist on site. These buildings are not secured against entry and are in serious disrepair. Loose boards and nails could pose a physical hazard to trespassers.

This document was made available for public comment for a period of 33 days. Public comments and concerns are listed and addressed in Appendix H.

3.6.1 Data Gaps

Game animal tracks have been observed on tailings piles and in the former poison pond area. Hunters are known to hunt on or near the site. A group of approximately 20 mushroom hunters were observed on the site in the past as well (Schuld 2002). Other than fish and macro invertebrates, no biota sample results are available for plants and animals present on the site. Game and plants in the mine area may have been exposed to site contaminants. It is not possible at this point in time to evaluate the potential health threat posed by human consumption of game and plants harvested from the site.

There are no environmental sample results for past exposures during mining activities. Residents of the town of Stibnite and mine workers may have been exposed to contaminants released from mining, ore processing, and smelting activities. These exposures could have resulted from ingestion of and dermal contact with soils and water. Additionally, it is not possible to evaluate the degree and magnitude of past exposures to airborne contaminants in the smelter stack emissions.


4. PATHWAYS OF HUMAN EXPOSURE

BEHS evaluates the environmental and human components that lead to exposure. Human contact with environmental contamination is only possible when a completed exposure pathway exists. A completed exposure pathway exists when all of the following five elements are present: (1) a source of contamination; (2) transport through an environmental medium; (3) a point of exposure; (4) a route of human exposure; and (5) an exposed population.

The source of contamination is the place where the chemical contamination originates. Sources can include storage tanks or drums, waste dumps, streams, ponds, or chemical processing facilities. Chemicals can move through environmental media such as soil, air, and water. Chemical contaminants are also transported from the source by accumulating in plants and animals. A point of exposure is the location where humans come into contact with the contamination. Points of exposure are areas where people can come into contact with contaminated environmental media. Points of exposure at Stibnite include contaminated creeks, tailings piles, or discharge pipes. A route of exposure is a way a chemical contaminant can enter a person's body. Breathing, eating, drinking, and skin contact are all routes of exposure. People who come into contact with a chemical through one or more routes of exposure are considered part of the exposed population. The exposed population for this site includes past, present, and future site workers, recreationists, and former residents of Stibnite.

It is important to note that if a completed exposure pathway exists, a public health hazard is not necessarily present. If an exposure to contaminated air, water, soil, or biota occurs, the exposure dose must be sufficient enough to cause a health effect in order to pose a health risk. If the dose is too low to cause a potential health effect, there will likely be no health risk, even if an exposure pathway is complete.

ATSDR categorizes an exposure pathway as completed if all five elements above exist and indicate that exposure to a contaminant has occurred in the past, is currently occurring, or will occur in the future. A potential pathway, however, requires that at least one of the five elements is missing, but could exist. Potential pathways indicate that exposure to a contaminant could have occurred in the past, could be occurring now, or could occur in the future. An exposure pathway can be eliminated if at least one of the five elements is missing and will never be present. Table 1, Table 2, and Table 3, in the following sections, summarize the pathways for the Stibnite site. The discussion following these three tables concentrates on the pathways that are of public health significance and relevant to the site. Eliminated pathways are briefly described.

4.1 Completed Exposure Pathways

A completed exposure pathway requires all of the five elements to be present (a source of contamination, transport through an environmental medium, a point of exposure, a route of human exposure, and an exposed population). Table 1 lists the completed exposure pathways for the Stibnite site.

Table 1.

Completed Exposure Pathways
Source Media Point of Exposure Route of Exposure Exposed Population Time Status
Stibnite Mine Area onsite surface soil tailings, neutralized ore, waste rock, smelter cinder piles, heap leach pile, old crusher area roads & air field eating,
skin contact
site workers, recreational users, former residents of Stibnite past completed
present completed
future potential
Stibnite Mine Area surface water Blowout and Meadow Creeks, seeps, Glory Hole, EFSFSR, old crusher area roads & air field drinking,
skin contact
site workers, recreational users, former residents of Stibnite past completed
present completed*
future potential
Stibnite Mine Area sediment banks of Blowout and Meadow Creeks, Glory Hole, EFSFSR, old crusher area roads & air field eating,
skin contact
site workers, recreational users, former residents of Stibnite past completed
present completed
future potential
Stibnite Mine Area air
dust
depositional areas in Meadow Creek Valley, the Glory Hole, and along the EFSFSR, old crusher area roads & air field breathing site workers, recreational users, former residents of Stibnite past completed
present completed
future potential

* This pathway is currently completed for dermal contact and is potentially complete for drinking.

4.1.1 Onsite Surface Soil

Spread out over the 3,000 acre site are various waste rock dumps, neutralized ore piles, exposed tailings piles, and capped tailings piles. Contaminants of concern in the site surface soils are arsenic, antimony, lead, and mercury (Appendix C, Table C-2 and C-3). Some of the depositional areas are less than an acre, while others (such as the Meadow Creek Mine hillside) are over 100 acres. The exposed tailings piles, former smelter stack site, heap leach pile, and some of the waste rock dumps are visibly different from the surrounding landscape. Color staining is visible in these exposed areas. Other areas, such as the capped Bradley tailings and neutralized ore piles and capped impoundments in Meadow Creek Valley, are not visibly different from the rest of the area.

A completed exposure pathway for surface soil currently exists and existed in the past. Past mining practices combined with the presence of mine workers and their families likely lead to multiple exposures, both chronic and acute. Tailings, neutralized ore, waste rock, and smelter cinders were deposited in open areas and were not capped until recently. Past levels of exposure are unknown but it is likely that past exposures were greater than the present exposure scenario.

Currently, a completed pathway exists for reclamation workers, recreational users, and trespassers contacting surface soils on the site. Hunters, sport anglers, hikers, campers, and other recreational users visit the site and are observed frequenting the Glory Hole, the Meadow Creek Valley, and the banks of the EFSFSR. Additionally, Hecla employs seasonal reclamation workers for their closure activities. A future potential exposure pathway for soil could exist depending on the extent of closure and reclamation activities and future erosion of the Meadow Creek Mine hillside and the slopes surrounding the Glory Hole. Recreational users are likely to be exposed to contaminated surface soils in the future since there is no current plan to cap and revegetate all of the contaminated areas.

4.1.2 Surface Water

A completed surface water pathway existed in the past and currently exists at the site through skin contact and drinking (ingestion). There are multiple streams and creeks in the area as well as seasonal seeps and the Glory Hole. The seeps are seasonal from spring until summer when they dry up. In general, many of the seeps are difficult to access, except those emanating from the Bradley tailings and neutralized ore pile near the keyway wetland. Mine tailings, neutralized ore, and waste rock deposited in and around the streams and seeps have been eroded by surface waters throughout the history of the site. Until all waste piles are stabilized and capped and the stream channels stabilized, this erosion will continue into the future. This erosion of waste piles increases the metal loads of the site surface water.

Measured concentrations of arsenic and antimony in the streams and some seeps exceed the CVs for drinking water (Appendix C, Table C-4). Contaminants of concern in the site surface waters are arsenic, antimony, and manganese (Appendix C, Table C-4). Surface water and seeps are not used for drinking water at the site. Yellow Pine's public water system (PWS) utilizes a surface water intake from the Boulder Creek, approximately 15 miles downstream. There have been no reported MCL violations for the PWS in the past 10 years.

Although the site surface waters are not known to be used as a source of drinking water, it is possible that recreational users (past, present, and future) utilize the surface waters as a drinking water source. Additionally, it is possible that site workers, former residents of Stibnite, and recreational users have, do, or will come into contact with site surface waters while wading through streams or even swimming in the Glory Hole.

4.1.3 Sediment Pathway

Past mining activities led to the deposition of neutralized ore, waste rock, and tailings directly into the site streams. As a result, stream sediments are elevated in metals. A completed sediment exposure pathway exists currently, as well as in the past. Unless the sediments are removed, or capped, exposure to contaminated sediments may occur in the future. Exposed individuals include site workers, recreational users, and past residents of Stibnite. Recreational users and former residents could have contacted, or even accidentally ingested, contaminated sediment while fishing, wading in streams, or swimming in the Glory Hole.

4.1.4 Air and Dust Pathway

Wind erosion of surface materials, as well as soil disturbance from mining activities, such as rock crushing and ore hauling, while the mine was active introduced soil particles into the air. These activities would have constituted a completed exposure pathway for site workers and residents of the town of Stibnite in the past through inhalation of contaminated soil particles. Workers and residents of Stibnite were likely exposed to smelter stack emissions during the period the smelter was in operation.

Current activities at the site including reclamation activities, transporting personnel and equipment, and recreation also create dusty conditions, introducing soil particles into the air. These activities represent a completed pathway for recreational users and site workers through inhalation. Future activities at the site, including reclamation, transportation, and recreation may introduce particulate matter into the air constituting a potential future pathway for recreational users and site workers who may inhale potentially contaminated soil particles in the air.

4.2 Potential Exposure Pathways

A potential exposure pathway is defined as one where exposure could be possible except that one or more of the five elements is missing (a source of contamination, transport through an environmental medium, a point of exposure, a route of human exposure, and an exposed population). In some cases, this means that the exposure is not possible now but may be possible in the future. In other cases, an exposure may be possible but cannot be confirmed because data are not available. The potential pathways for the Stibnite site are summarized in Table 2.

Table 2.

Potential Exposure Pathways
Source Media Point of Exposure Route of Exposure Exposed Population Time Status
Stibnite Mine Area biota fish
game
plants
eating consumers of fish, game, or plants past potential
present potential
future potential

4.2.1 Biota - fish, game, and plants

A potential exposure pathway exists for individuals who consume biota such as fish, game, and plants taken from the site. Those individuals could include sports fishermen, hunters, gatherers and their families and friends who share the caught, hunted, or collected food. It is not known how much fish, game, or plants is caught, hunted, or collected on the site for human consumption.

Game tracks were observed and photographed at the Bradley tailings piles and at the former poison pond areas. In the past, site reclamation workers and government agency employees observed a group of approximately 20 mushroom hunters camping in the Meadow Creek Valley Game hunters are also occasionally observed crossing the site boundaries. Reportedly, whitefish is the only species of fish found in site surface waters that is not designated as a catch and release fish. Therefore, whitefish is the only fish species at the site that the Idaho Department of Fish and Game allows anglers to keep and consume.

Since there are no comparison values for contaminants in fish, BEHS considers all the measured contaminants in fish as contaminants of concern (Appendix C, Table C-5).

Although biota exists at the site and recreationists have been observed fishing, hunting, and collecting at the site, the degree of bioaccumulation in site biota is unknown, as is the rate of human consumption of animals and plants taken from the site. While the potential exists for past, present, and future exposure to site contaminants through the consumption of site biota, the extent and magnitude of the potential exposure is currently unknown. It is possible that the rate of fishing, hunting, and collecting will increase as closure activities are completed and the site is left vacant.

4.3 Eliminated Pathways

Eliminated exposure pathways are defined when exposure is unlikely and one or more of the five elements is missing (a source of contamination, transport through an environmental medium, a point of exposure, a route of human exposure, and an exposed population). This means that the exposure is not possible now and it is not likely to be possible in the future. The eliminated pathways for the Stibnite site are summarized in Table 3.

Table 3.

Eliminated Exposure Pathways
Source Media Point of Exposure Route of Exposure Exposed Population Time Status
Stibnite Mine Area onsite subsurface soil Stibnite Mine Area eating
skin contact
former mine workers and current workers conducting closure activities past potential*
present eliminated
future eliminated
Stibnite Mine Area ground water onsite well and past onsite wells drinking
skin contact
site workers and past site residents past potential*
present eliminated
future eliminated

* This exposure pathway was potentially completed for former residence of Stibnite and completed for former mine workers.

4.3.1 Subsurface Soil

Human exposure to contaminated subsurface soils (soils beneath the site) is not expected for the present or the future. Current site activities are concentrated on site closure. Mining activities are not expected to resume in the future. Site subsurface soils contain elevated concentrations of metals such as arsenic, antimony, cadmium, lead, and mercury. It is likely that former mine workers were exposed to subsurface soils during mining operations, completing the pathway for subsurface soil. Residents of Stibnite were potentially exposed to subsurface soils during past mining activities, however, it is not possible to determine the extent and magnitude of past exposures for former workers and residents at this time. Consequently, the subsurface soil pathway was eliminated from further consideration.

4.3.2 Groundwater

There are no active groundwater wells within 15 miles of the site. Results of the 1997 and 1999 sampling data indicate that the groundwater at Stibnite contains concentrations of antimony and arsenic in excess of the MCLs for drinking water. However, since groundwater at the site is not currently utilized as a drinking water source and is unlikely to serve as a drinking water source in the future, this pathway was eliminated from consideration.

In 1992, the site drinking water well, located approximately one mile from the former processing plant, exceeded the MCLs for arsenic. The extracted groundwater from this well was passed through a commercial deionizer filtration unit before it was distributed for drinking. After passing through the deionizer, the concentration of arsenic was below the MCL. During the 1992 season, between 50 and 120 employees used the groundwater from the site well as a drinking water source from May to November.

Former mine workers and residents of Stibnite used this groundwater as a drinking water source. However, the location of the single drinking water well prevented it from being exposed to mining related contaminants present in surface and ground water (Schuld 2002). This well is secured against use but has not been abandoned. It will be properly abandoned when closure activities are completed. It is possible that former mine workers and residents of Stibnite were exposed to unknown levels of naturally occurring arsenic in their drinking water.


5. DISCUSSION - ADULT AND CHILDREN'S HEALTH ISSUEs

After reviewing the site-specific data and information, there are four completed and one potential exposure pathways which people could be or could have been exposed to chemicals from the site. Health effects can only result from site contaminants when people come in contact with them in sufficient doses. The public health implication of the exposures is discussed in the following sections. In Section 5.1, the actual exposures to these contaminants of concern (selected from Section 3) (Appendix C) are evaluated using estimates of exposure and the toxicological properties and epidemiological information about these chemicals. As a part of the ATSDR Child Health Initiative, and in response to community concerns, the susceptibility of young children or developing fetuses to the chemical exposures will be part of the toxicological and epidemiological review.

5.1 Public Health Implications

5.1.1 Introduction

In order to understand the health effects that may be caused by a specific chemical, three factors affecting how the human body responds to exposure needs to be considered. These factors include exposure concentration, the duration of exposure, and the route of exposure. Lifestyle factors can affect the likelihood of exposure and the exposure duration. Individual characteristics of each human such as age, sex, nutritional status, and overall health can affect how a contaminant is absorbed, distributed, metabolized or eliminated from the body. Together, these factors determine the individuals' response to chemical contaminants and what health effects may occur for that person.

To evaluate health effects, ATSDR developed Minimal Risk Levels (MRLs) for contaminants commonly found at hazardous waste sites. The MRL is an estimate of daily human exposure to a contaminant below which non-cancerous, adverse health effects are unlikely to occur. MRLs are developed for each route of exposure, such as inhalation and ingestion, and for the length of exposure, such as acute (less than 14 days), intermediate (15-364 days), and chronic (greater than 365 days). Acute MRLs are typically higher than chronic MRLs because of the shorter duration of exposure. BEHS also uses EPA's chemical-specific Reference Doses (RfDs) to determine if non-cancer health effects are possible. RfDs, similar to ATSDR's MRLs (Appendix C, Table C-6), are estimates of daily human exposure to a contaminant that is unlikely to result in adverse non-cancer health effects over a lifetime. For chemicals that are considered to be known, probable, or possible human carcinogens, BEHS uses EPA's chemical-specific cancer slope factors to calculate a theoretical excess lifetime cancer risk. These risks are associated with the exposures that are based on conservative, or protective, exposure assumptions. The cumulative cancer risk of the same contaminant from exposure to multiple environmental media is added together for a total risk estimation.

For determining possible exposures to contaminants in soil, maximum concentration or reasonable maximum exposure concentration in surface soil were used. The exposure scenarios for children were based on the older children (7 years or older) playing or camping at the Stibnite site. BEHS assumed that only older children would be among hunters, sport anglers, hikers, campers, and other recreational users who visit the site. It was also assumed that all recreational users would spend 8 days per year at the site, while a shorter exposure frequency of 1 day per year is used for small hot spot areas, such as the smelter stack and Location UW1 in the Upgradient Wetland, assuming that a future recreational user would visit the area only once. The reclamation workers are assumed to work for 4 months (mid-June through mid-October), 5 days per week, for a total of 90 days. Reclamation and monitoring programs are likely to be conducted during a 5-day work week (or less frequently). This exposure frequency is an alteration from former active mining operations which included a mine worker active 7 days per week. A shorter exposure frequency of 14 days is used for the hot spots small areas such as the smelter stack and location UW-1 in the Upgradient Wetland, assuming that, at most, 14 days would be required for any reclamation activity in these areas. Mining operations ceased in 1998 and are not expected resume in the future.

Exposure duration, body weight, and age are used to estimate the amount of contaminants that might have entered a person's body. The assumptions used to calculate exposure for an older child (7 -18 years of age) is a body weight of 45 kg (approximately 100 pounds) and a soil ingestion rate of 200 mg per day. The assumptions for an adult are a body weight of 75 kg (approximately 165 pounds) and a soil ingestion rate of 100 mg per day. Those estimates were chosen in reference to the Exposure Handbook (EPA 1997) and ATSDR's guideline with some Idaho-specific adjustments. Instead of the standard EPA body weight assumption (70kg), BEHS uses the median Idahoan body weight of 75kg to better represent people in Idaho (BVRHS 2001). In addition, the maximum concentration or reasonable maximum exposure concentration found in surface soil was used for calculating risks and doses, so a worst-case scenario was evaluated.

There are no air sampling concentrations to use for determining possible exposure to contaminants in the air and windblown dust. Consequently, BEHS doubled the soil ingestion rates to calculate the inhalation exposure dose, assuming that exposure dose from air particulates is the same as that from ingestion of surface soil. This is a very conservative assumption since the exposure dose from inhalation of airborne particulates is normally much lower than the exposure dose from ingestion of surface soil.

To determine possible exposure to contaminants in drinking water, maximum contaminant concentrations or reasonable maximum exposure concentrations found in surface water samples were used to calculate risks and doses to be protective of public health. Water consumption rates are assumed to be 2 liters per day (L/day) for all the future recreational users (children aged 7 through adults). For the reclamation workers, BEHS assumes that they will not use the local surface water as their drinking water.

For determining possible exposure to contaminants in fish, maximum contaminant concentrations or reasonable maximum exposure concentrations of fish fillets were used. Fish fillets are the part of fish most likely to be consumed by humans. A fish intake rate of 25 g per day was used for the general recreational consumption of whitefish (all other species are classified as catch and release). This value is in the 95th percentile nationwide for recreational anglers (freshwater fish). For subsistence recreational users, a fish intake rate of 58.7 g per day was used (CRITFC 1994). Fish tissue was analyzed for total arsenic. However, most arsenic in fish was present in non-toxic organic forms. It was reported that 10 percent of total arsenic in freshwater fish is in the inorganic form (URS 2002). However, we still use the total arsenic as inorganic arsenic, so a worst-case scenario was evaluated.

ATSDR generally considers dermal exposure to be a minor contributor to the overall exposure dose relative to the contributions of ingestion and inhalation exposures, BEHS did not calculate the dermal exposure dose. BEHS considered the bioavailability of arsenic to be 80% in Smelter Stack and 60% in all other places (EPA 2000), and 100% for other contaminants. All assumptions are summarized in the following Table 4.

Table 4.

Exposure Assumptions Summary
Exposure Assumptions Populations
Recreational Users Reclamation Workers
7<Children<18 Adults>18
Body Weight (kg) 45 75 75
Exposure Frequency (days/year) Hot Spots 1 1 14
Other Areas 8 8 90
Exposure Duration (years) Hot Spots 1 1 1
Other Areas 12 30 1
Averaging Times (days) for Noncarcinogenic Hot Spots 365 365x30 365
Other Areas 365x12
Averaging Times (days) for Carcinogenica Hot Spots 365x70 365x70 365x70
Other Areas
Surface Soil Ingestion Rate (mg/day) 200 100 100
Air Particulate Double the soil ingestion rate to include the air particulate inhalation
Surface Water Consumption Rate (L/day) 2 2 0
Fish Fish Intake Rate (g/day) 25b 25b 25

a: assumes average lifetime is 70 years.
b: for general recreational users, the fish intake rate is 25 g per day, while the fish intake rate is 58.7 g per day for tribe recreational users.

5.1.2 Evaluation of Toxicology and Epidemiology by Pathway

Health-based CVs are established at concentrations below which no known or anticipated adverse human health effects are expected to occur. BEHS first compared the measured media contaminant concentrations with the corresponding CVs (Appendix C). The contaminants with media concentrations higher than their CVs became the contaminants of concern. Exceeding a CV does not mean that health effects will occur, just that more evaluation is needed. Once the contaminants of concern are selected, exposure doses are calculated for each exposure pathway. Exposure dose calculations can be found in Appendix C for non-cancerous doses and Appendix D and E for carcinogenic doses.

5.1.2.1 Surface soil and airborne particulate exposure pathway

As discussed before, since there are no air contaminants concentrations, BEHS doubled the soil ingestion rates to calculate the total exposure dose from both surface soil ingestion and airborne particulate inhalation. For most areas, antimony and arsenic are above the comparison values, while lead in Location UW1 in the Upgradient Wetland and mercury in the smelter stack area are also above the comparison values (Appendix C, Table C-2 and C-3).

Surface Soil and Airborne Particulate Exposure Pathway : Non-Cancer Risk Evaluation

Antimony

In most areas, the possible antimony exposure dose is lower than 0.0004 milligrams per kilogram per day (mg/kg/day) (the chronic oral RfD) (Appendix C, Table C-7 and C-8), except for: child recreational users at location BD6 (Northwest Dump hotspot) (0.0004 mg/kg/day), reclamation workers at BD6 (Northwest Dump hotspot) (0.0017 mg/kg/day), Meadow Creek Forested Wetland (0.001 mg/kg/day), and Lower Meadow Creek Valley (0.00087 mg/kg/day). The exposure to antimony at BD6 (Northwest Dump hotspot) is an acute exposure for both child recreational users and reclamation workers, while the exposures at Meadow Creek Forested Wetland and Lower Meadow Creek Valley are intermediate exposure for reclamation workers. The RfDs for both acute and intermediate oral exposures are normally higher than the chronic oral RfDs. Health effects have been observed in humans and animals following oral exposure to a variety of antimony compounds. However, the no-observed-adverse-effect levels (NOAELs) or lowest-observed-adverse-effect levels (LOAELs) in all the related studies are equal to or higher than 0.0748 mg/kg/day (ATSDR 1992). Pre and postnatal exposure or only postnatal exposure alone to 0.0748 mg/kg/day of antimony as antimony trichloride appears to affect the development of certain cardiovascular reflexes in rats that are important for regulating systemic arterial blood pressure. The highest possible exposure dose from ingestion of surface soil and inhalation of air borne particulate is 44 times lower than 0.0748 mg/kg/day (the lowest NOAELs and LOAELs). On the other hand, BEHS supposes that the exposure dose from inhalation of air borne particulates is the same as the dose from ingestion of surface soil, which is a very conservative assumption since the exposure dose from inhalation of air borne particulates is normally much lower than the exposure dose from ingestion of surface soil. BEHS uses the maximum concentration or reasonable maximum exposure concentration to estimate the exposure dose, which is very conservative for chronic and intermediate exposure. The actual exposure dose will be much lower than the estimated highest daily exposure dose. Consequently, BEHS does not expect elevated non-cancer health risks from exposure to antimony in the surface soil at the site for the present land users.

Arsenic

While the arsenic concentrations are all above the comparison values, the estimated exposure doses (non-carcinogenic) are very different for different land users (Appendix C, Table C-7 and C-8). For the adult recreational users, the estimated arsenic exposure doses are all below the chronic oral MRL (0.0003 mg/kg) (Appendix C, Table C-6), which means arsenic in the surface soil would not likely result in any non-carcinogenic public health effects for the adult recreational users. For child recreational users, the estimated exposure doses from arsenic in all areas are lower than the chronic oral MRL except at the Southeast Dump & Midnight Creek, the Northeast Dump & Sugar Creek, Glory Hole & Northwest Dump & EFSFSR. For child recreational users, the estimated exposure doses from arsenic at the Southeast Dump & Midnight Creek, the Northeast Dump & Sugar Creek, as well as Glory Hole & Northwest Dump & EFSFSR are 6 to 16 times lower than the acute oral MRL (0.005 mg/kg/day), respectively (Appendix C, Table C-6). The recreational users are assumed to visit these sites 8 days per year, which is categorized as an acute exposure. BEHS uses the maximum concentration or reasonable maximum exposure concentration to estimate the exposure dose. BEHS assumes that the exposure dose from inhalation of air borne particulates is the same as the dose from ingestion of surface soil. All these assumptions are over protective, or conservative. It is unlikely that the arsenic in the surface soil will result in any adverse non-carcinogenic public health effects on the children recreational users.

For the reclamation workers, in two-thirds of the exposure locations on site, the non-carcinogenic exposure doses of arsenic from ingestion of surface soil and inhalation of air borne particulates are higher than chronic oral MRL while 2 to 13 times lower than acute oral MRL. The exposure time for reclamation workers is 14 or 90 days per year, which is categorized as an acute or intermediate exposure. As a note, the contaminated dumping area was covered with relatively uncontaminated soil, preventing exposure to contaminated surface soil. Ingestion of surface soil or inhalation of airborne particulates mainly comes from the relatively uncontaminated covering materials instead of the contaminated surface soil. However, to be protective, BEHS uses the maximum concentration or reasonable maximum exposure concentration to estimate the exposure dose and assumes that the exposure dose from inhalation of airborne particulates is the same as the dose from ingestion of surface soil. Because BEHS uses a conservative approach, actual exposure doses of arsenic will be much lower than the estimated doses. It is unlikely the arsenic in the surface soil will result in any adverse non-cancer public health effect for the reclamation workers.

Mercury

Only the maximum mercury concentration (471 mg/kg) in the Smelter Stack surface soil is higher than the comparison value. However, the highest estimated exposure dose (Appendix C, Table C-8) is 59 times lower than ATSDR's intermediate oral MRL (Appendix C, Table C-6), which means no adverse public health effects from the mercury in surface soil are expected.

Lead

Among all the lead concentrations in the surface soil at Stibnite, only the maximum lead concentration (754 mg/kg) at Location UW-1 (Upgradient Wetland hotspot) is higher than EPA's Residential Soil Preliminary Remediation Goals (400mg/kg). There are no MRLs or RfDs for lead. However, for the oral and inhalation pathways, the lowest NOAEL among all the related studies is 0.0015 mg/kg/day (ATSDR 1999). The estimated exposure doses (Appendix C, C-6) for child recreational users, adult recreational users and reclamation workers are 83, 270 and 27 times lower than the lowest NOAEL respectively. BEHS uses the maximum concentration at Location UW-1 (Upgradient Wetland Hotspot) to estimate the exposure dose and assumes that the exposure dose from inhalation of airborne particulates is the same as the dose from ingestion of surface soil. Because these exposure doses are overly protective, actual exposure doses of lead will be lower than the estimated doses. Furthermore, a 1 to 8 day exposure at Location UW-1 (Upgradient Wetland hotspot) is assumed for all the present land users. Thus, it is unlikely that lead in the surface soil will result in any adverse public health effects to the present land users.

Surface Soil and Airborne Particulate Exposure Pathway: Cancer Risk Evaluation

Some chemicals have the ability to cause cancer. Cancer risk is estimated by calculating a carcinogenic exposure dose (Appendix E) and multiplying it by the cancer slope factor (Appendix F). Cancer risk estimates are not definitive answers to whether or not a person will get cancer; rather, they are measures of chance (probability). Cancer is a common illness, and there are many different forms of cancer that result from a variety of causes; not all are fatal. Approximately one quarter to one third of people living in the United States will develop cancer at some point in their lives. EPA considers arsenic to be a known human carcinogen based on evidence that human exposure through drinking water can cause skin, bladder and lung cancer (ATSDR 2000). BEHS calculated the estimated carcinogenic exposure doses of arsenic and the corresponding cancer risk (Appendix D, Table D-1). The estimated highest cancer risk is about 17 cancer estimated for 100,000 persons exposed. BEHS uses the maximum concentration or reasonable maximum exposure concentration to estimate the exposure dose and assumes that the exposure dose from inhalation of air borne particulates is the same as the dose from ingestion of surface soil. All of these are very protective assumptions. Actual risks are likely to be lower. Furthermore, this is only theoretical risk, considering the relatively small group of people living (there are only 40 people in the nearest town Yellow Pine), visiting and working (a seasonal workforce of approximately six to eight people at Stibnite) at the Stibnite area, the predicted increased risk of cancer from arsenic in the surface soil is so low as to be negligible.

5.1.2.2 Surface water exposure pathway

It is possible for the future recreational users to consume the surface water as their drinking water, while it is unlikely that reclamation workers will use surface water as a source of drinking water. Manganese concentrations are above the comparison value only in Keyway Wetland surface water, while the concentrations of antimony and arsenic are higher than their comparison values in most areas except the Upgradient Wetland (Appendix C, Table C-4).

Surface Water Exposure Pathway: Non-Cancer Risk Evaluation

The estimated daily exposure doses for manganese, arsenic, and antimony (Appendix C, Table C-9) are all below ATSDR's chronic oral MRL or EPA's chronic oral RfDs (Appendix C, Table C-6) with the exception of Bailey Tunnel Outlet for Child recreational users. The actual exposure at Bailey Tunnel Outlet for child recreational users is categorized as an acute exposure. The estimated exposure dose (0.00031 mg/kg/day) is 16 times lower than the acute oral MRL. BEHS uses the maximum concentration or reasonable maximum exposure concentration to estimate the exposure dose, a very protective assumption. The water ingestion assumption of 2 L per day for all the exposure days is also very protective of human health. The contaminants in the surface water will unlikely result in any adverse non-cancer public health effects for the recreational users and are not expected to be a public health concern.

Surface Water Exposure Pathway: Cancer Risk Evaluation

The carcinogenic exposure doses are listed in Appendix D, Table D-1. Cancer risk is estimated by calculating a carcinogenic exposure dose (Appendix E) and multiplying it by the cancer slope factor (Appendix F). Cancer risk estimates are not definitive answers to whether or not a person will get cancer; rather, they are measures of chance (probability). The estimated highest cancer risk for surface water exposure is about 12 cancer estimated for 100,000 persons exposed. BEHS uses the maximum concentration or reasonable maximum exposure concentration to estimate the exposure dose and assumes that recreational users consume 2 L surface water per day for all the exposure time. Actual risks are likely to be lower. This is only theoretical risk, considering the relatively small group of people living near and visiting the Stibnite site. The predicted increased risk of cancer from arsenic in the surface water is so low as to be negligible.

5.1.2.3 Potential fish exposure pathway

Potential Fish Exposure Pathway: Non-Cancer Risk Evaluation

Since there are no comparison values for contaminants in fish, BEHS calculated estimated daily exposure doses (Appendix C, Table C-5) for all the contaminants. For general recreational users, the estimated exposure doses are 556, 19000, 111, 581, and 3160 times lower than the corresponding ATSDR's chronic oral MRLs or EPA's chronic oral RfDs (Appendix C, Table C-6), for arsenic, manganese, methyl-mercury, selenium and zinc, respectively. For reclamation workers, the estimated exposure doses are 83, 2857, 17, 86, and 517 times lower than the corresponding chronic oral MRLs or RfDs. There is no MRL or RfD for lead. Nevertheless, the estimated highest exposure doses for lead from fish are 2935 (for general recreational users) and 429 (for reclamation workers) times lower than the lowest NOAEL among all the related studies (0.0015 mg/kg/day) (ATSDR 1999). The consumption of fish for the recreational users and reclamation workers is not expected to be a public health concern.

As to the local tribe recreational users, their average daily fish consumption rate is 58.7 grams per day (CRITFC 1994), which is about 2.5 times that of general recreational users. Their estimated exposure doses are 237, 8092, 47, 247, 1346, and 1250 times lower than the corresponding ATSDR's chronic oral MRLs, EPA's chronic oral RfDs, or the lowest NOAEL among all the related studies, for arsenic, manganese, methyl-mercury, selenium, zinc, and lead respectively. Thus, even for the local Native American recreational users, the consumption of fish is unlikely to result in any adverse non-cancer risk.

Potential Fish Exposure Pathway: Cancer Risk Evaluation

The estimated highest cancer risk for consumption of fish is about 2 (for general chid recreational users) and 5 (for tribe child recreational users) cancer cases estimated for 10,000,000 persons exposed; a slight increase in cancer risk. Considering the relative small group of people living near and visiting the Stibnite site, the predicted increased risk of cancer from arsenic from consumption of fish is so low as to be negligible.

5.1.2.4 Summary of health risks from the multiple pathways

A person can be exposed to contamination through more than one pathway and to more than one chemical. Exposure to multiple pathways occurs if a contaminant is present in more than one medium (i.e., air, soil, surface water, groundwater, and sediment). For example, the exposure dose received from drinking water may be combined with the exposure dose received from contact with that same contaminant in soil.

The exposure doses and cancer risks for the same contaminant from different pathways are listed in Table C-10 (Appendix C) and Table D-1 (Appendix D). From the Tables, we can see the total exposure doses and cancer risks for the same contaminants are similar for ingestion of surface soil and inhalation of air borne particulates. This means that most exposure doses and cancer risk result from the ingestion of surface soil and inhalation of airborne particulates. More particularly, the highest total exposure doses and cancer risks for the same contaminants are exactly the same as that from ingestion of surface soil and inhalation of air borne particulates. As stated in Section 5.1.2.1, the contaminants are not expected to result in any adverse public health effects, and the predicted increased risk of cancer from arsenic is so low as to be negligible.

According to the reclamation workers, even though it is estimated that reclamation will be completed in one season (90 days), some workers have been doing reclamation out there for up to 7 years. For non-cancer risk, since this will not change the highest estimated exposure doses, it is unlikely to result in any adverse non-cancer risk as stated in Section 5.1.2.1. For cancer risk, we further add together all the estimated cancer risk from all locations (Appendix D, Table D-1) assuming the same workers will finish all the reclamation by finishing one site per working season. The estimated highest cancer risk for the reclamation workers would be 2 cancer cases estimated for 10,000 workers exposed. This is only theoretical risk. Considering there is only a seasonal work force of 6 to 8, the predicted increased risk of cancer from arsenic is so low as to be negligible.

5.1.3 ATSDR Child Health Considerations

Children differ from adults in their physiology (e.g., respiratory rates relative to body weight), pharmacokinetics (i.e., distribution, absorption, metabolism, and excretion of chemicals), and pharmacodynamics (i.e., susceptibility of an organ to the exposure). Therefore, it is always important to address chemical exposures of these sensitive populations. Fetuses, infants, and children are more vulnerable to the toxic effects of chemicals because of the following reasons. 1) children are more likely to play outdoors and bring food into contaminated areas; 2) children are closer to the ground (shorter), resulting in a greater likelihood to breathe dust, soil, and heavy vapors laying on the ground; 3) children weigh less resulting in higher doses of chemical exposure per body weight; and 4) the developing body system can sustain permanent damage if toxic exposures occur during critical growth stages.

It is unlikely that younger children (<7 years old) will visit the Stibnite site as recreational users. It is a concern for older children who come to swim or camp with their parents in some areas of the site. As a prudent public health practice, BEHS has made recommendations to mitigate or eliminate exposure to site-related contamination even though exposure is not expected to cause adverse health effects. BEHS's recommendations are summarized in Section 7.

5.2 Health Outcome Data (HOD) Evaluation

The main requirements for evaluating HOD are the presence of a completed human exposure pathway, high enough contaminant levels to result in measurable health effects, a sufficient number of persons in the completed pathway for health effects to be measured, and a health outcome database in which disease rates for population of concern can be identified.

Although completed human exposure pathways exist at this site, the exposed population is not large enough to permit meaningful measurements of possible site-related health effects as identified in existing HOD. According to the 2000 US Census, the population of Yellow Pine, 14 miles away from the site, is 40 people. Only a fraction of those residents are expected to regularly visit the site as recreational users. The site itself has no permanent residents. Hecla maintains a seasonal workforce of approximately four people at the Stibnite site for approximately five months of the year during late Spring through early Fall.

5.2.1 Community Health Concerns

On June 26, 2003, BEHS held a public availability session in Yellow Pine to share the preliminary results of the draft public health assessment and to gather community health concerns. Members of the general public were invited to review and comment on the draft public health assessment from June 25 until July 28, 2003. Representatives of IDEQ, EPA, and USFS indicated that the community was mainly concerned with retaining access to the site and avoiding the stigma of living next to a Superfund site. BEHS confirmed these concerns when meeting with community members and when reviewing the public comments on the draft public health assessment. The only health concern expressed by a single community member was the possibility of bioaccumulation of contaminants in plants and game animals at the site. Other concerns were strictly ecological or regulatory in nature. Community concerns are documented and addressed in Appendix H.


6. CONCLUSIONS

  1. The completed exposure pathways identified include: surface soil, surface water, airborne particulates and sediments. The most important exposure pathway is the ingestion of surface soil and inhalation of airborne particulates. As there are no air contaminant concentrations available, and to be protective of public health, BEHS assumes that the exposure dose from inhalation is the same as from ingestion of surface soil. Consumption of fish is a potential exposure pathway, while subsurface water and ground water are eliminated exposure pathways.

  2. There is no information available about former mine workers, thus BEHS is unable to evaluate their past exposures and the public health implications of these exposures.

  3. It is unlikely that the contaminants at the Stibnite site will result in any adverse public health effects for the reclamation workers and recreational users, since the estimated exposure doses are either below the corresponding health guideline values, or below the corresponding lowest NOAELs (or LOAELs) in all the related studies. The predicted increased risk of cancer from arsenic is so low as to be negligible to the reclamation workers and recreational users.

  4. According to ATSDR's Interim Public Health Hazard Categories, the exposure pathways related to surface soil and sediment, airborne particulates, surface waters, and fish are categorized as no apparent public health hazard (Appendix B). However, the public health hazard posed by the consumption of biota (other than fish) cannot be evaluated at this time due to a lack of data and information, which is categorized as an indeterminate public health hazard.

  5. This report conclusion only applies to the current reclamation workers and recreational users. If land use changes, this conclusion might not be applicable.

7. RECOMMENDATIONS

  1. As a precaution, signs should be posted at the access points to the site informing visitors of the presence and potential health threat of site contaminants.

  2. BEHS should provide health education materials to the populations that use the site about potential health impacts of the Stibnite site.

  3. The reclamation workers should be cautious about ingestion of surface soil and surface water.

  4. Hot spot remediation is prudent even though BEHS does not believe that exposures will result in any adverse public health effects to the recreational users and reclamation workers

  5. Biota (other than fish) samples should be collected and analyzed for potential uptake of metals from site soils and surface water.

8. PUBLIC HEALTH ACTION PLAN

The purpose of the public health action plan is to ensure this public health assessment not only identifies any current and potential exposure pathways and related health hazards, but also to provide a plan of action to mitigate and prevent adverse human health effects resulting from exposures to hazardous substances in the environment. The following lists the ongoing or planned actions by BEHS, IDEQ and other agencies.

  1. BEHS will conduct health education activities to inform Yellow Pine residents of the status of the site. Recommendations against using the site for recreation will also be made.

  2. BEHS will assist the USFS and EPA with their community involvement plan as necessary.

  3. BEHS forwarded this document to HECLA and brought attention to the third recommendation, referring to their site workers.

  4. BEHS will review additional environmental sampling data as it becomes available.

  5. BEHS will request that the regulatory agencies involved with this site implement the fifth recommendation. If the agencies are unable to fulfill this request, BEHS and ATSDR will explore the feasibility of conducting an exposure investigation with regard to site biota.

  6. IDEQ is negotiating institutional controls with the current site owners to prevent future development of the site.

  7. IDEQ is negotiating with the site owners about how to prevent public exposure to the onsite contamination. Possible actions include site access restriction, posting warning signs, and site reclamation. Reclamation activities will focus on securing tailings piles and other contamination in such a way that the public and eco-receptors (biota) can utilize the area without the threat of exposure.

  8. IDEQ will require that the mill building containing mineral extraction equipment and chemicals be removed and properly disposed of along with process chemicals.

  9. IDEQ will arrange to have damaged buildings on site removed if they interfere with site reclamation or pose a significant threat to site safety.

9. REFERENCES

ATSDR 1992. Toxicological Profile for Antimony. US Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry, Atlanta, GA.

ATSDR 1999. Toxicological Profile for Lead (update). US Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry, Atlanta, GA.

ATSDR 2000. Toxicological Profile for Arsenic (update). US Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry, Atlanta, GA.

BVRHS 2001. Idaho Behavioral Risk Factors. Bureau of Vital Records and Health Statistics, Division of Health, Idaho Department of Health and Welfare. Boise, ID.

Census Bureau 2000, Census 2000 Summary File. Valley County, Idaho. http://www.census.gov/Press-Release/www/2001/sumfile1.html

CRITFC 1994. A Fish Consumption Survey of the Umatilla, Nez Perce, Yakima, and Warm springs Tribes of the Columbia River Basin.

EPA 1997. Exposure Factors Handbook, Volume I, General Factors. EPA/600/P-95/002Fa. Office of Research and Development, US Environmental Protection Agency, Washington, DC.

EPA 2000. Region 10 Guidance for Superfund Human Health Risk Assessment, Interim.

IRIS 1998. Integrated Risk Information System Substance File - Inorganic Arsenic (CASRN 7440-38-2), http://www.epa.gov/iris/subst/0278.htm . US Environmental Protection Agency, Washington, DC.

Schuld, B. 2002. Mine Project Coordinator, Idaho Department of Environmental Quality, E-mail communication with Aaron Scheff, Health Educator, Bureau of Environmental Health and Safety, Division of Health, Idaho Department of Health and Welfare, Boise, ID.

URS 2000, Stibnite Area Risk Evaluation Report, URS Corporation, Stibnite Area Site Characterization Voluntary Consent Order Respondents, Denver, CO.

USFS 1993, Preliminary Assessment/Site Investigation, Stibnite Mining Area, CERCLIS ID. NO. ID9122307607 , US Forest Service, Payette National Forest, Idaho.


10. PREPARERS OF REPORT

Report Authors

Lijun Jin, Public Health Assessor/Toxicologist
Aaron Scheff, M. Ed., Manager - Environmental Health Education and Assessment Program


Reviewers

Elke D. Shaw-Tulloch, M.H.S., Chief - Bureau of Environmental Health and Safety

Environmental Health Education and Assessment Program
Bureau of Environmental Health and Safety
Division of Health
Idaho Department of Health and Welfare
450 W. State Street, 4th Floor
P.O. Box 83720
Boise, Idaho 83720-0036


ATSDR Technical Project Officer

Gregory V. Ulirsch, M.S., Environmental Health Engineer

Division of Health Assessment and Consultation
Superfund Site Assessment Branch
Agency for Toxic Substances and Disease Registry
1600 Clifton Avenue, Mailstop E-32
Atlanta, Georgia 30333


ATSDR Regional Representatives

Karen L. Larson, Ph.D., Regional Representative

Office of Regional Operations, Region X
Agency for Toxic Substances and Disease Registry
1200 Sixth Avenue, Room 1930 (ATS-197)
Seattle, WA 98101


11. CERTIFICATION

The Idaho Bureau of Environmental Health and Safety prepared this Public Health Assessment under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the Public Health Assessment was initiated.

Gregory V. Ulirsch
Technical Project Officer, SSAB, DHAC


The Superfund Site Assessment Branch (SSAB), Division of Health Assessment and Consultation (DHAC), ATSDR has reviewed this health consultation and concurs with its findings.

Roberta Erlwein
Chief, SSAB, DHAC, ATSDR



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