From the early 1900s until 1982, the Blackbird Mine was an active mining facility located in Lemhi County, Idaho. Acid mine drainage and runoff from site surface deposits have resulted in arsenic and other heavy metals being released into Panther Creek and other area surface waters . Full time and seasonal residents live along Panther Creek in the flood plain area. In addition, some residents have used Panther Creek as a source for irrigating their land.
The U.S. Environmental Protection Agency (EPA) collected soil and sediment samples along the banks of Panther Creek in 1997. Environmental sampling showed maximum levels of arsenic at 3,500 parts per million (ppm) in surface soils and 280 ppm in sediments. Currently, the EPA is over-seeing a removal action at the Blackbird Mine site.
In 1997, the Idaho District Seven Health Department and the Idaho Department of Health and Welfare requested assistance from the Agency for Toxic Substances and Disease Registry (ATSDR) to investigate actual and potential exposure to inorganic arsenic among residents living near or adjacent to Panther Creek or Panther Creek Road (See Appendix A: Site Maps). In addition, residents of Salmon, Idaho, who lived or worked near and along Panther Creek or Panther Creek Road since May 1997 were also included in this exposure investigation.
This exposure investigation included both biological testing and selected environmental sampling (See Appendix B: Panther Creek Exposure Investigation Protocol). The biological testing included the collection of urine and hair samples to determine inorganic arsenic levels. The measurement of urinary inorganic arsenic is most often used to quantify exposures within a few days prior to urine collection and the measurement of inorganic arsenic in hair is most often used to quantify past exposures within a few months prior to hair collection. Environmental samples were collected at residential and public use areas (e.g., camp sites, picnic areas, commercial areas) to determine levels of arsenic and other metals in surface soils, drinking water, and indoor dust (See Appendix D: Environmental Sampling Methods and Procedures). Environmental sampling was only offered to residents currently living near or along Panther Creek or Panther Creek Road.
Results from this investigation were used to identify appropriate follow-up health activities for participants whose biological testing or environmental sampling results indicated elevated levels of arsenic or other metals. As a public health investigation, rather than a research study, these results are applicable only to the Panther Creek Exposure Investigation participants and are not generalizable to other populations.
On October 20 and October 21, 1997, public availability sessions were held in Cobalt and Salmon, Idaho, respectively (See Appendix D: Fact Sheets, Questionnaire, etc.). At the sessions, questions about the exposure investigation were addressed. Informed consent forms were completed by adult and minor participants. Urine collection kits and daily activity questionnaires were explained and given to participants. Participants were asked to record their activities for three days, and provide a first morning void urine sample on the fourth day. Consenting participants had a hair sample (at least 50 milligrams) collected by a stylist (See Appendix D: Instructions for collecting a hair sample). Participants were offered environmental sampling at their residential properties.
Urine and hair samples were evaluated from people living or working along or near Panther Creek and Panther Creek Road. For those residents presently living in Salmon, Idaho, who had spent time along Panther Creek or Panther Creek Road during the previous summer, only hair samples were collected.
The analytical method used in this exposure investigation includes the analysis for inorganic arsenic and its metabolites (monomethylarsonic acid and dimethylarsinic acid). This method does not test for arsenobetaine and arsenocholine (non-toxic fish arsenic). The urinary inorganic arsenic test is adjusted for individual creatinine levels to account for variations in urinary dilution.
Levels of urinary inorganic arsenic in unexposed populations are below 50 micrograms (mg) total inorganic arsenic per gram (g) creatinine [2-6]. Levels exceeding this value are considered elevated. Since inorganic arsenic absorbed into the body is taken up into keratin rich hair, hair arsenic levels can provide quantification of an individual's average arsenic exposure during the growth of the hair tested. A time reference of exposure can be obtained because hair grows approximately one inch every two months with some variation from individual to individual and between males and females. Seafood consumption is not considered to significantly affect total arsenic levels in hair because the non-toxic forms of fish arsenic are not absorbed into the hair. Arsenic levels in hair below one microgram of arsenic per gram of hair (1 ppm) are considered to be typical of background levels in unexposed populations . Levels exceeding this value are considered to be elevated. Analysis of hair may yield misleading results due to the presence of arsenic adsorbed to the external surface of the hair, but this can be minimized by collecting samples from close to the scalp or from unexposed areas, and by washing the hair before analysis . The laboratory that conducted the hair analysis for this exposure investigation added an additional rinse step to the hair sample as part of their analytical protocol before the hair was analyzed for inorganic arsenic .
Environmental samples were collected from 13 residential properties and 10 public use areas (See Appendix E: Public use areas-environmental sampling locations, etc.). Residential environmental sampling was offered only to participants currently residing along Panther Creek or Panther Creek Road. The environmental sampling locations were selected based upon input from the U.S. Forest Service, the Idaho District Seven Health Department, and information acquired from residents. Some of the properties and wells (private and/or public) were sampled based on their potential impact from mine tailings by either being located within the Panther Creek flood plain, or if the property used the creek as a source for irrigation. Other properties and wells (private and public) sampled were not located within the flood plain, and the properties had not used Panther Creek as a source for irrigation. These properties were selected based on requests from the U.S. Forest Service and concerned citizens.
A total of thirty-two surface soil, 46 indoor dust, and 12 drinking water samples were collected from the 13 residential properties. Twenty-five surface soil and five drinking water samples (one from a recreational use water source) were collected from public use areas.
Surface soil and indoor dust samples were analyzed for arsenic, copper, cobalt, chromium, cadmium, antimony, uranium and lead. The drinking water samples were analyzed for arsenic, copper, cobalt, chromium, cadmium, and lead.
Reporting the Panther Creek Exposure Investigation Results
In late November 1997, participants received by mail their biological testing and environmental sampling results. A fact sheet was included with the testing results explaining ways to reduce potential exposures to arsenic and other metals in indoor dust and/or surface soils. A follow-up public availability session was held in Salmon, Idaho, on December 17, 1997. Representatives from the Idaho District Seven Health Department, Idaho Department of Health and Welfare, U.S. Forest Service, ATSDR, and EPA were present at the public availability session. The purpose of the session was to discuss the results and provide a forum for health and environmental officials to address questions from the participants.
The seven participants identified with elevated levels of inorganic arsenic in their hair samples were notified by Idaho Department of Health and Welfare. They were contacted by telephone and mail informing them of the December public availability session in Salmon. The seven participants were also informed that health evaluations were being offered free of charge by ATSDR at the Salt Lake City Association of Occupational & Environmental Clinic.
Exposure investigation participants whose properties had elevated arsenic levels were also notified by telephone and mail about the December public availability session in Salmon.
In February 1998, all exposure investigation participants and residents living in the Panther Creek drainage area were mailed a fact sheet summarizing the overall findings of the Panther Creek Exposure Investigation (See Appendix D: Fact Sheet-Update on the Panther Creek Exposure Investigation).
Biological Testing Results
Thirty-seven individuals participated in this exposure investigation. Twenty-two individuals submitted hair and urine samples. Fourteen participants only submitted hair samples, and one participant only submitted a urine sample. Table 1 summarizes the urinary inorganic arsenic results and Table 2 summarizes the hair inorganic arsenic results.
|Participants||Hair Inorganic Arsenic Values a|
|3||0.3, 0.4, 0.7|
|3||14.7, 21.9, 26.1|
| a [ppm] = parts per million |
Note: Reference hair value = 1 ppm inorganic Arsenic
Overall, the urine testing showed inorganic arsenic levels below the detection limit, or at levels that did not indicate that higher than average exposures were occurring [2-6]. The urine reference value used for comparison is 50 mg Arsenic/g creatinine . The urine results, with the information in the questionnaires, provide information on exposure and activities occurring 3 days prior to urine collection.
The results of the hair testing showed 25 individuals with inorganic arsenic levels below the detection limit. Three individuals had results less than the 1.0 ppm reference value; two individuals had results slightly greater than the 1.0 ppm reference value; and five individuals had inorganic arsenic levels greater than the 1.0 ppm reference value. All seven of the individuals showing elevated levels of inorganic arsenic in hair were working at the Blackbird Mine site. The elevated levels of inorganic arsenic in hair indicates that exposures to inorganic arsenic may have occurred in the previous two to four months.
Environmental Testing Results
Of the residential soils tested, only one soil sample was elevated for arsenic (1300 ppm). The remaining residential soil samples were within background concentrations. Background arsenic concentrations in soil range from 1 to 194 ppm . Elevated arsenic levels were more prevalent in indoor dust. Arsenic was detected at elevated levels (ranging from 120 to 460 ppm) in indoor dust at six residential properties. No elevated levels of arsenic or other metals were detected in any of the residential drinking water samples tested. See Table 3 below for a summary of the ranges of metals detected in the various environmental samples at residential properties.
An elevated level of uranium (830 ppm) was detected in one indoor dust sample collected from one residence. However, a dust sample collected from another location in the house did not contain an elevated uranium concentration, and uranium was not detected in two outdoor, surface soil samples. Therefore, there is no apparent source of uranium at this residence, and the limited area of dust contamination is not expected to pose a health hazard.
|Surface soils [ppm]||NDa - 1300 b||6.5 - 43||11 - 720||5.2 - 100||ND - 3.8||ND - 5.4||ND||ND - 80|
|Vacuum Indoor Dust [ppm]||ND - 460||9.2 - 41||12 - 750||ND - 240||ND - 130||ND - 3.7||ND -830c||8.5 - 160|
|Wipe Indoor Dust ug/wipe||ND - 52||ND - 22||1.1- 220||ND - 29||ND - 10||ND - 3.8||ND - 1.4||ND - 39|
| Drinking Water |
| <3 -26 |
| <0.06-0.262 |
| <5- 10 |
| <5 mean=<5 |
|NAe|| <0.03-0.4 |
|NA|| <1.0- 2.2 |
a ND= Not detected
Public Use Areas
Two composite surface soil samples collected from public use areas contained elevated concentrations of arsenic. These samples were collected from Panther Creek Inn (1100 ppm) and Panther Creek Inn Campsite (3500 ppm ). Two drinking water samples exceeded the U.S. EPA's maximum contaminant level (MCL) of 50 ppb for arsenic and EPA's action level of 15 ppb for lead. Panther Creek Campsite well water showed 64 ppb arsenic, and the Bacon Ranch had 19.8 ppb lead in the well water. Indoor dust samples collected at the Panther Creek Inn, Bacon Ranch, and an apartment at Moyer did not show elevated levels of arsenic or other metals. The Bacon Ranch and the apartment at Moyer are owned by the U.S. Forest Service. See Table 4 below for a summary of the ranges of metals detected in the various environmental samples at public use areas.
- There was no strong evidence of inorganic arsenic exposures among individuals tested living near Panther Creek or Panther Creek Road. However, there was evidence of inorganic arsenic exposure among seven workers involved in cleanup or exploration of the Blackbird Mine site. These seven adult males had elevated levels (ranging from 1.3 to 26 ppm) of inorganic arsenic detected in their hair samples.
- Arsenic was detected in surface soils at three residential properties and two public use areas (Panther Creek Inn and Panther Creek Inn Campsite Area) at levels that may pose a public health threat.
See Appendices E and F for the public health implication statements for these properties (the names and addresses associated with the residential properties are kept confidential).
- Arsenic was detected in indoor dust from six residential properties at levels that may pose a public health threat. Four of the residential properties with elevated levels of arsenic in indoor dust did not have elevated levels of arsenic detected in their surface soil samples. The elevated levels of arsenic detected in the indoor dust of these four homes were most likely the result of workers carrying contaminated dust home on their shoes and clothing from the Black Bird Mine site.
See Appendix F for the public health implication statements for these residential properties (the names and addresses associated with the residential properties are kept confidential).
- Elevated levels of arsenic were detected in well water from the Panther Creek Inn Campsite area. Elevated levels of lead were detected in the well water from the Bacon Ranch.
See Appendix E for the public health implication statements for these public use areas.
- Provide health evaluations and health education to the seven participants with elevated hair arsenic levels.
- Provide health education to residents with elevated levels of arsenic or other metals detected on their properties. The health education should focus on ways to reduce potential exposures to contaminated soil and dust through appropriate house keeping methods (e.g. wet mopping) and personal hygiene practices. (See Appendix D: Fact Sheets).
- Follow-up with the Blackbird Mine Site Group to ensure that employee exposure to contaminants is maintained below levels of health concern. Emphasis should be placed on implementing safety measures to prevent workers from carrying contaminated dust home on their shoes and clothing.
- Implement interim measures to prevent exposure to contaminated soil at the Panther Creek Inn and Panther Creek Inn Campsite until a permanent solution can be developed. EPA has agreed to implement interim measures by the Spring of 1998 prior to removal activities beginning the summer of 1998. The interim measures should prevent contamination of the indoor dust at these properties.
- Resample the wells at Panther Creek Inn Campsite and Bacon Ranch to verify if contamination is present. If followup sampling confirms elevated levels of metals, then consider the use of an alternative source for drinking water.
Note: On December 17, 1997, all the recommendations listed above were discussed with the participants of the Panther Creek Exposure Investigation and the appropriate health and environmental agencies at a public availability session held in Salmon, Idaho.