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. Although other metals are discussed, this public health consultation will focus on lead, since that is the element for which data are readily available. This health consultation deals with land areas that are currently unpopulated. However, it is likely that children and other area residents could have access to areas in which the highest concentrations of lead are found. Because soil ingestion is greatest in infants and young children who engage in frequent hand-to-mouth activity, exposures of young children are of particular concern. Children living in areas that are currently populated have in the past been shown to have elevated blood lead levels (6).
The maximum concentration of lead detected was 65,600 milligrams/kilogram (mg/kg) in the West Wardner hillside surface soils (1). 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 a wide range of health 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 are, in fact, unlikely in the potentially exposed populations.
A remedial action objective (RAO) of no more than 350 mg lead/kg soil has been set for residential properties within the Bunker Hill site. The RAO for residential yard lead concentrations in new developments must average less than 350 mg/kg lead, with no yard exceeding 1,000 mg/kg lead (1). This level should be protective of public health in a majority of adults. Biologic monitoring data for lead indicate that mean blood lead level for area children is 5.4 micrograms of lead per deciliter of blood (µg/dL) (6). Approximately 8% of the children have blood lead levels greater than 10 µg/dL. National Health and Nutrition Survey (NHANES) III data indicate that the mean blood level for children in the United States is approximately 2.5 µg/dL (8). Blood lead levels among children in the Bunker Hill communities are already twice the national average, their future exposure to lead should be minimized. Care needs to be taken to educate the affected community about the adverse health effects of lead poisoning and its prevention.
The maximum concentration of arsenic (79 mg/kg) was detected in the surface soils on a shelf south of Smelterville (1). The chronic oral MRL for arsenic is 0.0003 mg/kg/day. The no observed adverse effect level (NOAEL) in humans is 0.0004 mg/kg/day. The estimated exposure doses for toddlers and children displaying pica behavior exceeds the NOAEL. Arsenic can produce noncarcinogenic effects, including gastrointestinal, cardiac, neurologic, and dermal effects.
Relatively little information is available on adverse health effects due to direct dermal contact with inorganic arsenicals, but several studies indicate that the chief effect is local irritation and dermatitis, with little risk of other adverse effects. The dermal contact rates which cause these effects in humans have not been quantified, but a similar type of irritation was produced on mice exposed to 2.5 mg arsenic/kg as sodium arsenite (10). Absorption of arsenic in soil through the skin is expected to be minimal and is not expected to produce adverse healing effects.
EPA classifies arsenic as a Class A known human carcinogen by the oral and inhalation routes. Epidemiologic studies of people exposed to arsenic in Taiwan indicate that exposure to arsenic is associated with skin cancer. On the basis of that and other studies, the EPA considers arsenic to be a human carcinogen. The EPA has calculated a cancer unit risk factor, 1.5 (mg/kg/day)-1, which can be used to estimate the probability of excess cancer risk for a lifetime of exposure to arsenic. Cancer risks for exposure at the hillsides site were estimated on the basis of the maximum concentration of arsenic in the contaminated hillside soils. The estimated lifetime cancer risk poses no apparent increased risk for affected residents of developing cancer. However, residents should take care to avoid direct contact with contaminated soils.
Since the degree of arsenic toxicity may be influenced by the rate and extent of its methylation in the liver, it seems likely that some members of the population might be especially susceptible because of their lower than normal methylating capacity. This reduced capacity could result from a dietary deficiency of methyl donors such as choline or methionine. Liver disease itself does not appear to decrease methylation capacity in humans, at least not at low levels of arsenic exposure.
Cadmium was detected in the surface soils of undeveloped hillsides at a maximum concentration of 21 mg/kg. The highest concentration was located on a shelf south of Smelterville, between Grouse Creek and Government Gulch (1). The chronic oral MRL for cadmium is 0.0002 mg/kg/day. The NOAEL in humans following chronic exposure is 0.0021 mg/kg/day. The estimated exposure doses for children displaying pica behavior and consuming 500 mg or greater of soil per day exceeds ATSDR's MRL. If such children were to consume large quantities of the contaminated soils, they would increase their risk of developing renal, musculo-skeletal, and hematological problems.
Cadmium is classified by EPA as a probable human carcinogen, according to epidemiological studies. The epidemiological studies indicate that cadmium may be a carcinogen via the inhalation route of exposure, with a resulting condition of lung cancer. The studies have focused on occupational settings and concentrations much higher than those found in the soils of the undeveloped hillsides. Inhalation exposures in the vicinity of the Bunker Hill site will be evaluated in a companion consultation dealing with surface soils and fugitive dusts.
Zinc was detected in hillside soil at a maximum concentration of 1,810 mg/kg. According to the 1995 sampling event, the highest concentration of zinc was found in the hillsides of Pinehurst (1). The intermediate MRL and the RfD for zinc is 0.3 mg/kg/day. A child displaying pica behavior and consuming greater than 2,500 mg/day of the contaminated soil would exceed the MRLs and the RfD. Possible adverse health effects may include decreased serum HDL cholesterol, decreased serum cortisol levels, and decreased hematocrit.
The main public health concern associated with the unpopulated hillsides 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 (6). Some of the children required medical treatment to reduce the amount of lead in their blood (chelation). Possible effects of elevated lead in the 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. For children displaying pica behavior, adverse health effects from exposure to arsenic, cadmium, and zinc are also possible. No significant increased risk of developing cancer is expected.
Although the samples discussed in this public health consultation were taken from unpopulated hillsides surrounding the Bunker Hill National Priorities List site, there is a chance that some of the properties will be developed in the future. In addition, the contamination discussed is in the surface soils of the hillsides; therefore, it is possible for run-off of these soils to contaminate or re-contaminate populated areas of the site.
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 hillside 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.
In studies of chronic exposure, children appear to be more severely affected by arsenic than adults, probably due to higher exposure per body weight (body burden). Unborn children can be exposed via transplacental migration. Neural tube defects are the most predominant and consistent malformations in mammalian species tested. The association between prenatal arsenic exposure and congenital malformations has not been fully established, but in light of arsenic's teratogenic potential in other mammalian species, humans are also likely to be vulnerable to these conditions as a result of arsenic exposure.