BUNKER HILL MINING AND METALLURGICAL
KELLOGG, SHOSHONE COUNTY, IDAHO
The primary exposure route at the site is most likely through incidental ingestion of contaminated soils. This health consultation deals with right-of-ways (ROWs). It is likely that contaminants from contaminated ROWs could be transported into populated areas (yards and homes). A companion public health consultation will look at those possible exposures via fugitive and house dusts. Because soil ingestion is greatest in infants and young children who engage in frequent hand-to-mouth activity and because of past reports of adverse health effects, exposures of young children are of particular concern. Children living in populated areas have, in the past, been shown to have elevated blood lead levels (3).
Many of the ROWs throughout the site were built using mine waste tailings. In order to prevent contamination or re-contamination of populated areas via vehicle tracking, structural integrity of the roadways must be maintained. An institutional controls program (ICP) that is a locally enforced set of regulations has been instituted for this purpose. The ICP is administered by the Panhandle Health District. The ICP contains regulations concerning construction and use-changes involving excavation and grading on all properties where barriers and caps have been installed.
Some potholes and other signs of degradation were seen during site visits conducted by ATSDR. In addition, some damage occurred as a result of flooding and storm events. The remedial action objective for the site is that there will be no soil lead level greater than 1,000 mg/kg. When areas of contamination are found, a barrier of no less than six inches is placed over the contaminated sub-surface soils and clean gravel (usually) is placed over the barrier.
During the sampling investigations, samples were taken at 0-1, 1-6, and 6-12 inch depths. This health consultation focuses on the results from testing of samples taken from the first two intervals (Appendix A), since those are the soils to which people are most likely to be exposed.
Soil samples were collected from right-of-ways in the town of Smelterville. Approximately 275 samples were collected from the top two intervals during the sampling periods and analyzed for lead. The concentration of lead in samples taken from the top zero- to one-inch interval ranged from 19 to 21,500 mg/kg. At least 30% of the location's samples showed concentrations of lead greater than 1,000 mg/kg. A majority of the high lead concentrations occurred south of Main Street, with the highest concentration being found near the end of Northview Avenue to the east of A Street. The maximum concentration of lead in the 1"-6" interval (36,900 mg/kg) was detected in the 1999 sampling event. This is more than twice the concentration that was detected in 1997. Since remediation in Smelterville was completed by 1997, these concentrations of lead in the top intervals indicate that re-contamination is occurring. Those areas with high lead levels could now serve as a source of re-contamination of other remediated areas in Smelterville.
Right-of-ways in Kellogg were sampled. One hundred and seventeen samples were collected. The samples were analyzed for lead content. The concentrations ranged from 20 to 126,000 mg/kg, with the highest concentrations being found in the six- to twelve-inch interval. The maximum concentration in the top zero- to one-inch interval was 11,100 mg/kg. The highest concentrations found in the top interval were collected from the southern portion of Kellogg on the south side of I-90. These sampled areas could serve as a source of contamination or re-contamination. The results may indicate that some barriers are not deep enough to prevent contaminant migration.
Union Pacific Railroad (UPRR) Right-of-Way
The UPRR right-of-way extends approximately 7.9 miles within the BHSS. The remediated bike path/railroad right-of-way in Kellogg was sampled. Twelve test pits were dug along the UPRR right-of-way, and 28 samples were collected and analyzed for lead content. The maximum concentration of lead found was 1,980 mg/kg. Sample concentrations in the top six-inch intervals did not exceed 457 mg/kg. These sample concentrations do not indicate a major source of contamination or re-contamination.
Fourteen samples were collected from the Pinehurst community in 1999. The maximum concentration of lead found in the top inch was 2,120 mg/kg. The maximum concentration found in the samples was 3,550 mg/kg (1- to 6-inch interval).
TOXIOLOGICAL EVALUATION OF LEAD (4)
The maximum concentration of lead detected was 21,500 milligrams/kilogram (mg/kg) in the top zero- to one-inch samples taken from Smelterville during the 1998 sampling event and 30,300 mg/kg in the top one- to six-inch samples taken from Kellogg during the 1998 sampling event (2). ATSDR has no minimal risk level (MRL) and EPA has no reference dose (RfD) for lead. The estimated exposure doses for children exceed the lowest observed adverse effect level (LOAEL) for neurological effects in monkeys (0.05 milligrams per kilogram per day (mg/kg/day)).
The level of lead in blood is a good measure of recent exposure, and it also correlates well with health effects. Exposure to lead causes a wide range of effects. Children are especially sensitive to lead, and many of its effects are observed at lower concentrations in children than in adults. Levels of 10 micrograms per deciliter (µg/dL) and perhaps lower in children's blood have been associated with decreased IQ, impaired hearing and growth, and some neurological effects. The neurological effects have been shown to persist after exposure has ceased and blood lead levels have returned to normal. The reported symptoms of the neurological effects include poor memory, difficulty reading and concentrating, depression, and sleep disturbances. Lead can significantly affect both the reproductive process and the development of the fetus in women with blood lead levels as low as 10 µg/dL. Documented effects include premature birth and low birth weight. In adults, levels as low as 15 µg/dL are linked to increased blood pressure, reduced production of sperm, earlier onset of menopause, and changes in the enzyme function in the blood.
The increased vulnerability of children results from a combination of factors, including the following:
- The increased susceptibility of the developing nervous system to the neurotoxic effects of lead,
- A higher average rate of soil/dust ingestion among children than among adults,
- The greater efficiency of lead absorption in the gastrointestinal tracts of children,
- The greater prevalence of iron or calcium deficiencies in children, deficiencies that may exacerbate absorption and the toxic effects of lead, and
- The ready transfer of lead across the placenta to the developing fetus.
Foods such as fruits, grains, meat, seafood, soft drinks, vegetables, and wine may contain lead. Cigarettes also contain small amounts of lead. While more than 99% of all drinking water contains less than 0.005 milligrams per liter lead, the amount of lead taken into the body through drinking water can be higher in communities with acidic water supplies. Children residing in older dwellings may also be exposed to lead by eating lead-based paint chips from peeling surfaces. This is particularly a problem in lower income communities.
Lead is classified by EPA as a Class B2 probable human carcinogen on the basis of animal studies. This classification reflects the fact that there is inadequate evidence to determine lead's carcinogenicity in humans. The estimated doses set for human cancer thresholds at the maximum concentration detected are 40 or more times lower than the levels shown to cause cancer in animals. Carcinogenic effects, in fact, are unlikely in the potentially exposed populations.
A remedial action objective of no more than 350 mg lead/kg soil has been set for residential properties within the BHSS. This level should be protective of public health in a majority of the cases. However, if a child displays extreme pica behavior (ingestion of 5,000 mg or more of contaminated soil), there is a chance that such a child could eventually display neurological deficits. Care needs to be taken to educate the affected community about lead poisoning prevention and adverse health effects.
The main public health concern associated with the right-of-ways at the Bunker Hill site is the potential exposure of children to lead. Past biological monitoring of children in the populated areas of the site indicates that some were exposed to lead above levels at which adverse health effects could possibly occur (3). Some of the children required medical treatment to reduce the amount of lead in their blood (chelation). Possible effects that may be caused by elevated lead in blood include decreased IQ and impaired hearing and growth. In addition, some neurological effects may occur and persist in the exposed children, even through adulthood. The reported symptoms of the neurological effects include poor memory, difficulty reading and concentrating, depression, and sleep disturbances. No significant increased risk of developing cancer is expected. With proper educational efforts and continued clean-up within the site, blood lead levels in children living in the affected communities should decline significantly.
The samples discussed in this public health consultation were taken from right-of-ways within the BHSS. The contamination discussed is near the surface of the right-of-ways; therefore, it is possible for run-off of these contaminants to re-contaminate remediated areas of the site. New drainage systems or improvements in current drainage systems may help alleviate some of the contamination and re-contamination that occurs because of run-off. Remediation at the site has been on-going since 1986. Recent data (Appendix A) indicate that re-contamination may be occurring over time. Many of the previously remediated ROWs have been re-contaminated and now exceed the remedial action objectives. Maintenance of failing road infrastructure is needed to prevent migration of contaminants from ROWs into populated areas where exposures are likely to occur.
Children are at greater risk than adults from certain kinds of exposure to hazardous substances emitted from waste sites. They are more likely to be exposed for several reasons. Children play outside more often than adults, increasing the likelihood that they will come into contact with chemicals in the environment. Since children are shorter and smaller than adults, they breathe more dusts, soil, and heavy vapors close to the ground, and exposures can therefore result in higher doses of chemical exposure per body weight. In addition, developing body systems of children can be damaged if toxic exposures occur during critical growth stages.
Children live within the area of the Bunker Hill Superfund site. ATSDR has considered possible exposure scenarios involving children while evaluating right-of way contamination.
Lead presents a significant health hazard to children. There is a significant difference between the pharmacodynamic and pharmacokinetic parameters for adults and children. Children are more vulnerable to lead exposure. Lead exposure is hazardous for unborn children and young children because they are more sensitive to lead during development. Moreover, unborn children can be exposed to lead via transplacental migration. Such exposures can cause premature births, smaller babies, and a decrease in a newborn's mental ability.
Children are more likely to experience lead-induced adverse health effects. They can absorb lead through the gastrointestinal tract more readily than adults. They also have immature detoxification enzyme systems that permit an increased body burden of lead once lead is ingested. In addition children have lower thresholds for adverse neurologic and hematologic effects from lead exposure.