PETITIONED HEALTH CONSULTATION
Residential Soil, Indoor Dust, and Ambient Air
ELIZABETH COPPER MINE
(a/k/a ELIZABETH MINE)
STRAFFORD, ORANGE COUNTY, VERMONT
BACKGROUND AND STATEMENT OF ISSUES
The Agency for Toxic Substances and Disease Registry (ATSDR) received a petition to address public health concerns from residents living near the Elizabeth Copper Mine Site in Strafford, Vermont. This health consultation addresses the sampling results for indoor dust, ambient air, and additional soil sampling conducted at three residences near the site.
The Elizabeth Copper Mine, now abandoned, operated sporadically from 1793 to 1958 producing iron sulfate and copper. The site contains open pit mines, extensive underground workings, three tailings areas, and several buildings. Tailings pile #1 (covering 30 acres) and #2 (covering 5 acres) consists of fine-grained tailings from a flotation mill which operated onsite from 1943 to 1958 [1]. Tailings pile #3 consists of coarser mine spoils and is a six-acre waste pile from earlier mining operations [1]. All three of the tailings piles are within one-half mile of the nearest residences.
Three families living along Old Mine Road, a dirt road adjacent to the site, have expressed concern that exposures to site-related contaminants are causing a variety of health problems including elevated blood lead levels. ATSDR previously issued health consultations addressing contaminants found in private drinking water wells and soil at these and other nearby residences [2,3].
In November 2000, EPA collected indoor dust and indoor wipe samples from each of three residences located on Old Mine Road [4]. Ambient air and residential soil samples were also collected in two of the three residential yards. All samples were analyzed for metals. ATSDR's evaluation of these samples (indoor dust, ambient air, and residential soil) follows.
Indoor Dust
The primary routes of exposure to contaminants in indoor dust are inhalation, dermal contact, and ingestion of contaminated foods (or mouthing of contaminated objects by toddlers and infants). Indoor dust samples were obtained using two different collection methods. The first method used a vacuum sampler to collect dust from a measured area on the floor in three different living spaces within each residence. In the second method, cloth wipes were used to collect dust samples at locations adjacent to the vacuum sample locations. The highest metal concentrations were primarily found in one sample location [4].
Lead
Based on the vacuum sample results, the lead concentrations detected in indoor dust ranged from non-detect to 1600 milligrams per kilogram per square meter (mg/kg/m2) [4]. ATSDR has not established a Minimal Risk Level (MRL) for lead nor has EPA established a reference concentration for lead. However, the EPA Office of Solid Waste and Emergency Response recommends a 400 milligrams per kilogram (mg/kg) screening level for lead in residential soil at Superfund sites [5].
In one of the three residences sampled, one indoor bulk dust sample indicated a lead level (1600 mg/kg) significantly greater than the 400 mg/kg screening level. This level does not appear to be representative of overall lead levels in the household dust. However, routine exposure to this highest lead level could cause adverse health effects, especially for young children.
The wipe samples indicated that lead loading (lead mass per surface area) ranged from 120-550 micrograms per square meter (µg/m2). For public housing, the U.S. Agency for Housing and Urban Development (HUD) defines a lead dust hazard as a lead level greater than 1080 µg/m2 on surface flooring (hard floors or carpeting) [6]. In a 1998 notice of proposed rule making, EPA defined a lead dust hazard as a level greater than 540 µg/m2 of lead on uncarpeted floors [7]. One of the dust wipe samples collected from the residence noted above showed a level of 550 µg/m2. This level slightly exceeds EPA's proposed definition of a lead dust hazard of 540 µg/m2 for child occupied facilities.
Iron
Dust samples contained levels of iron ranging from 7500 mg/kg to 19,000 mg/kg. ATSDR has not established an MRL for iron, however, these levels are less than the EPA Region III Risk Based Concentration (RBC) for iron in residential soil (23,000 ppm). RBCs are daily exposures that are not expected to result in any adverse health effects [8]. ATSDR does not anticipate that adverse health effects would occur from exposure to iron in dust at these levels.
Aluminum, Antimony, Arsenic, Cadmium, Chromium, Manganese, and Zinc
Public health agencies have not established screening values for indoor dust levels of aluminum, antimony, arsenic, cadmium, chromium, manganese, and zinc. However, the highest concentration found for each of these contaminants is less than the respective ATSDR soil screening value for potentially adverse health effects in children (non-pica). As a result, ATSDR does not expect any adverse health effects in children or adults as a result of exposure to the levels of these metals found in indoor dust.
For example, the concentrations of arsenic detected in the dust samples ranged from 1-7 ppm. All of the detected levels of arsenic in indoor dust are less than ATSDR's soil screening value for chronic non-cancer effects in children (20 ppm). These arsenic levels do exceed the soil screening value of 0.6 ppm for pica children. However, the screening value for pica children is based on consumption of 5000 milligrams (or 5 grams) of soil per day and contains a safety factor of three.
Pica is defined as an appetite for substances having no nutritional value, e.g., clay, dried paint, starch, or ice [9]. True pica behavior in children is relatively rare (< 1%), and sporadic, and is typically exhibited only during the first few years of life. It is not to be confused with the common habit of all babies and toddlers to mouth objects. Pica children actually swallow large amounts of non-nutritive materials; their intentional ingestion of soil, for example, is assumed to be 25 times the incidental ingestion of soil by non-pica children and 50 times that of adults. These values are on the high end and overestimate average soil consumption rates (by a factor of 2 or more) for most children.
Children are not likely to find or eat, 5-15 grams of household dust on a daily basis. The ATSDR Environmental Media Evaluation Guides (EMEGs) for arsenic in soil and water were based on a Taiwanese drinking water study. Since arsenic is several times more bioavailable in drinking water than in soil or dust, the soil EMEGs, which do not take bioavailability into account are more conservative than the drinking water EMEGs which are based on the same study and assume 100% bioavailability. The true margin of safety in all of ATSDR's EMEGs for arsenic (including the soil value for pica children) is substantially greater than the uncertainty factor of three would suggest. As a result, no adverse health effects would be expected to result from the ingestion of house dust containing 1-7 ppm arsenic, even if a child finds and consumes several grams of household dust every day.
The concentrations of total chromium detected in indoor dust ranged from 15-51 ppm. Like those for arsenic, these levels were less than the ATSDR Reference Dose Media Evaluation Guide (RMEG) soil screening value for chronic non-cancer effects in children (200 ppm). However, the chromium levels found exceed the RMEG for pica children. The reference dose (RfD) on which this RMEG was based contains a composite safety factor of 900. Therefore, it would be virtually impossible for any child to find and eat enough contaminated household dust (more than one pound per day) to get a dose equivalent to the Lowest Observed Adverse Effects Level (LOAEL) for chromium. The LOAELs are exposure levels associated with adverse health effects that may be serious or relatively subtle.
Another consideration is that the RMEG for chromium addresses the more toxic hexavalent chromium [Cr(VI)]. In environmental samples, trivalent chromium [Cr(III)] levels are typically seven times higher than Cr(VI) levels. As a result, we would expect that most of the chromium found in the household dust is the less toxic Cr(III).
Magnesium, Phosphorus, Sodium, Titanium
No public health standards have been established for magnesium, phosphorus, sodium, and titanium in dust or soil. However, magnesium, phosphorus, and sodium are major mineral nutrients; children need about 150, 800, and 200 mg, respectively, in their daily diet. Due to its low toxicity, titanium and several of its compounds are used in medical therapies for skin disorders as well as in implant materials in orthopedics, oral surgery, and neurosurgery. Therefore, ATSDR does not anticipate any adverse health effects from exposure to these constituents at the levels found in the indoor dust samples.
Ambient Air
Five ambient air samples were collected near two homes located downwind of the tailings piles. Three samples were collected from one yard and two samples were collected from another.
Lead
Lead was found at 0.18 micrograms per cubic meter (µg/m3) near each home. This level is more than 60 times lower than the lowest lowest-observed-adverse-effect levels (LOAEL) found for humans exposed to lead via inhalation (11 µg/m3 ) [10]. As a result, ATSDR does not expect any adverse health effects to occur as a result of the levels of airborne lead found at these residences.
Chromium
Chromium (total) was found in the ambient air near one residence at levels of 0.56 µg/m3 and 0.27 µg/m3. Chromium was also present in the lot blank at 1.4 µg which may indicate that actual ambient chromium levels were lower than the results show. Total chromium includes trivalent chromium [Chromium III or Cr(III)] and the much more toxic hexavalent chromium [Chromium VI or Cr(VI)]. The levels of chromium found in the residential samples exceed the ATSDR Cancer Risk Evaluation Guide (CREG) for cancer effects for hexavalent chromium of 0.00008 µg/m3.
The concentration of total chromium in air [both Cr(III) and Cr(VI)] generally ranges between 0.01 and 0.03 µg/m3 [10]. The arithmetic mean concentrations of total chromium in the ambient air in the United States, urban, suburban, and rural areas monitored during 1977-1984 ranged from 0.005 to 0.525 µg/m3 [11,12]. The highest level of total chromium measured at the Elizabeth Mine site (0.56 µg/m3) is slightly above this range.
Chromium is released into the atmosphere mainly by man-made sources such as the combustion of natural gas, oil, and coal. Only a very small percentage (0.2%) of these chromium emissions are estimated to consist of the more toxic hexavalent chromium (Cr(VI) [13]. Therefore, the highest level of Cr(VI) found in ambient air near one residence could be estimated at 0.00122 µg/m3 (0.2% of 0.56 µg/m3). Since this level is higher than ATSDR's screening level (0.00008 µg/m3), further explanation is needed.
Hexavalent chromium [Cr(VI)] is a known human carcinogen via the inhalation route. The lowest concentration of chromium in air [a mix of Cr(III) & Cr(VI)] reported to be associated with elevated rates of lung cancer in humans is 40 µg/m3 [13]. However, the exposures in that study were occupational and lasted from 1 to 49 years [13,14]. The ATSDR CREG of 0.00008 µg/m3 was extrapolated from apparent effects levels observed in another occupational study [15] and assumes a threshold of zero. It represents a hypothetical 1-in-a-million "risk" level. However, the zero-threshold assumption is not likely to be applicable to Cr(VI) exposure. Inflammation is considered to be essential for the induction of most chromium-induced respiratory effects. Therefore, inflammation may be a necessary precursor for Cr(VI)-induced lung cancer which would suggest that a threshold may exist for the carcinogenic effects of chromium. The lowest human cancer effects level for chromium is 40 µg/m3 which is 20 times higher than the lowest LOAEL for non-cancer respiratory effects (2 µg/m3). Therefore, the highest level of total chromium found near a residence is more than three times lower than the lowest LOAEL for total chromium. Similarly, the highest level of total chromium found is more than 70 times lower than the lowest cancer effect level for total chromium.
Although EPA Region I has not established a comparison value for chromium, the EPA Region III Risk Based Concentration for trivalent chromium [Cr(III)] is 5500 µg/m3 for non-cancer health effects [7]. This level is almost 10,000 times greater than the levels found in the residential samples. As a result, no adverse effects would be expected from exposure to the maximum level of total chromium (0.56 µg/m3).
Residential Soil
Surface soil samples were collected from three residential yards and two background locations [16].
Arsenic
The highest level of arsenic found in any sample collected from a residential yard was 15.8 parts per million (ppm). [An estimated level of 18.3 ppm was also reported.] Although this level exceeds the most conservative ATSDR comparison values for chronic oral exposure to arsenic, it is not a level that is expected to cause adverse health effects.
Using the highest level of arsenic found (15.8 ppm), the estimated ingestion dose for a 10-kilogram (kg) child consuming 200 milligrams (mg) of this maximally contaminated soil every day is 0.00032 mg/kg/day. This estimated dose is more than two and a half times lower than the No-Observed-Adverse-Effect-Level (NOAEL) on which ATSDR's Minimal Risk Level (MRL) is based [17]. Neither oral nor dermal health effects from exposure to arsenic levels found in residential soil are expected to be a public health concern.
ATSDR's chronic Environmental Media Evaluation Guides (EMEGs) for arsenic in soil are 20 ppm (child) and 200 ppm (adult) and have a built-in safety factor. These EMEGs were derived, using default values for body weight and soil ingestion rate, from ATSDR's MRL of 0.0003 mg/kg/day (with an uncertainty factor of three). The MRL, derived from a Taiwanese drinking water study, may not be relevant to the potential adverse health effects of drinking water exposures in U.S. populations [17]. Also, arsenic in soil is less bioavailable (< 10%) than arsenic in water (>80%) [17]. Soluble, more readily absorbed, forms of arsenic tend to either be trapped in the soil matrix or leached out by rain, leaving the relatively insoluble, less readily absorbed, forms in the soil. Therefore, the MRL's effective safety margin is much greater for the ingestion of arsenic in soil than for arsenic in drinking water.
For example, the concentrations of arsenic detected in the soil samples ranged from 0.7-18.3 ppm. All of the detected levels of arsenic in indoor dust are less than ATSDR's soil screening value for chronic non-cancer effects in children (20 ppm). These arsenic levels do exceed the soil screening value of 0.6 ppm for pica children. However, the screening value for pica children is based on consumption of 5000 milligrams (or 5 grams) of soil per day. Children are not likely to eat 5-15 grams of soil on a daily basis. The ATSDR EMEG for arsenic used here is the same EMEG used in the previous evaluation for indoor dust. Again, this EMEG is based on a Taiwanese drinking water study. Since arsenic is several times more bioavailable in drinking water than in soil or dust, the soil EMEGs, which do not take bioavailability into account are conservative. The true margin of safety in all of ATSDR's EMEGs for arsenic (including the soil value for pica children) is substantially greater than the safety factor of 3. As a result, no adverse health effects are expected to result from the potential ingestion of the residential soil sampled.
Iron
Iron levels ranging from 12,400 ppm to 170,000 ppm (an average of 51,000 ppm) were found in the soil samples collected from three residential yards. Many of these levels exceed the EPA Region III Risk Based Concentration (RBC) for residential soil (23,000 ppm). RBCs are daily exposures that are not expected to result in any adverse health effects [8].
Based on the highest concentration of iron found in the soil, the estimated daily intake from soil ingestion for a child (non-pica) is 34 milligrams per day (mg/day). This amount of iron is 3.4 times greater than the U.S. Department of Agriculture (USDA) Recommended Dietary Allowance (RDA) for iron in children (10 mg/day) [18]. However, using the average iron concentration of 51,000 ppm, a child consuming 200 mg soil per day would also ingest 10.2 mg iron per day. Actual soil consumption is much less than 200 mg per day for most children and the bioavailability of iron in soil is likely to be less than that of iron in food. In addition, the body normally reduces absorption of iron from the gastrointestinal tract in response to higher concentrations. As a result, the levels of iron found in the soil are not likely to pose a health hazard to children.
Although ATSDR considers it extremely unlikely, it is conceivable that a pica child could ingest enough of the most-heavily contaminated soil to be exposed to an acutely toxic dose of iron. However, to the authors' knowledge, no case of acute iron toxicity has ever occurred as a direct result of soil consumption. The absence of such cases probably reflects the large amount of contaminated soil that would have to be ingested combined with the much lower intestinal absorption of iron from soil than from food.
Thallium
The highest level of thallium found was 2.6 ppm. This level is less than the EPA Region III RBC for residential soil (5.5 ppm) [8].ATSDR has not derived any acute, intermediate, or chronic-duration oral Minimal Risk Levels (MRLs) for thallium because no data on effects of chronic-duration oral exposure to thallium were located.
The maximum estimated soil ingestion exposure dose of thallium for a 10-kg pica child at this site is estimated at 0.0013 mg/kg/day. This estimated dose is based on the highest thallium level found among all the residential samples collected. Animal studies indicate a NOAEL of 0.20 mg/kg/day of thallium [19] which is almost 154 times greater than the highest estimated dose that could be expected from exposure to residential soil levels. Therefore, the thallium levels found are not expected to cause acute or chronic adverse health effects in children or adults.
Copper
Copper levels found in residential soils ranged from 19.2 ppm (estimated value) to 4690 ppm (estimated value). Only one value (4690 ppm) exceeded the Region VI Human Health Screening Levels for copper in residential soils (2900 ppm) [20].
In general, most copper in soil is in mineral form or tightly bound to organic matter. ATSDR does not expect that the copper levels found at the site are likely to pose an adverse health threat based on oral or dermal exposure.
Lead
The levels of lead found in the residential soil samples ranged from 11.2 to 316 mg/kg. These levels do not exceed the EPA screening level (400 mg/kg) and are not expected to pose a health hazard.
ATSDR'S CHILD HEALTH INITIATIVE
ATSDR's Child Health Initiative recognizes that the unique vulnerabilities of infants and children require special emphasis in communities faced with environmental contamination. At this site, sampling has identified lead, iron, arsenic, chromium, and copper as contaminants of concern. Children are particularly sensitive to the harmful effects of lead. ATSDR has taken into account that children live near the site and could be exposed to site-related contaminants.
Based on the best available public health practice, the blood lead levels of children younger than six living in Residence #2 should be tested periodically (a minimum of annually).
Table 1. Off-site Exposure Pathway Elements
Elizabeth Copper Mine Site
| Pathway Name | Exposure Pathway Elements | Time Frame | ||||
| Source | Media | Point of Exposure | Route of Exposure | Exposed Population | ||
| Completed Exposure Pathways | ||||||
| Indoor Dust | Elizabeth Copper Mine site (ECMine) | Indoor Dust | Residential homes near the ECMine | Ingestion | Residents near the ECMine | Past; Current; Future |
| Air (ambient) | ECMine | Ambient Air | Ambient air near the ECMine | Ingestion; Inhalation; Dermal |
Residents near the ECMine | Past; Current; Future |
| Soil | ECMine | Surface Soil | Residential surface soil near the ECMine | Ingestion, Dermal |
Residents who disturb surface soils near the ECMine | Past; Current; Future |
Gail E. Scogin
Environmental Health Scientist
Petitions Response Section
Exposure Investigation and Consultations Branch
Division of Health Assessment and Consultation
Frank C. Schnell, PhD.
Toxicologist
Petitions Response Section
Exposure Investigation and Consultations Branch
Division of Health Assessment and Consultation
Reviewed By:
Donald Y. Joe, P.E.
Chief, Petitions Response Section
Exposure Investigation and Consultations Branch
Division of Health Assessment and Consultation
