Superfund and Mining Megasites Lessons from the Coeur d'Alene River Basin (2005) / Chapter Skim
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5 Human Health Risk Assessment in the Coeur D'Alene River Basin
5 Human Health Risk Assessment in the Coeur D'Alene River Basin
Pages 161-222
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From page 161... ...
Environmental Protection Agency (EPA) and its partners followed in conducting the Coeur d'Alene River basin HHRA (TerraGraphics et al.
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From page 162... ...
For example, the Coeur d'Alene River basin HHRA identifies children as the primary population of concern for lead exposure and identifies the presence of local American Indian populations. Potential pathways of exposure are defined, such as children ingesting soil and house dust contaminated with lead, and American Indian ingestion of locally grown foods contaminated with lead.
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or reference dose. But for many compounds found at Superfund sites, much less is known, and there are myriad assumptions made that often prove very controversial.
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Geographic Area Considered in the Coeur d'Alene River Basin HHRA The Coeur d'Alene River basin HHRA considered an area that included the South Fork of the Coeur d'Alene River, its tributaries, and the main stem of the river west of its confluence with the North Fork. The region of interest spans roughly 53 miles from the Idaho-Montana border to Lake Coeur d'Alene and excluded the 21-square-mile Bunker Hill Superfund site.
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.1 CHEMICALS OF CONCERN IN THE COEUR D'ALENE RIVER BASIN: HAZARD IDENTIFICATION The database of environmental chemical analyses available for the HHRA process was extensive and included thousands of analyses of metals in soil, house dust, groundwater, homegrown vegetables, sediment, surface water, fish, and edible wild plants (water potatoes) in the river basin.
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From page 166... ...
The river basin HHRA considered which COPCs might pose a human health risk for each medium of possible exposure: soil/sediment, tap water, surface water, groundwater, house dust, air, fish consumption, and homegrown vegetables. The process used was very typical of any HHRA at sites where chemical exposures might occur.
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APPROACH USED TO ASSESS HUMAN HAZARDS: EXPOSURE ASSESSMENT After identifying which chemicals might pose hazards to human health, the HHRA set out to characterize human exposure. Because the concentrations of metals in various media and exposure profiles in the river basin are not uniform, EPA considered it necessary to divide the region of interest into nine distinct geographical areas: lower basin, Kingston, side gulches, Osburn, Silverton, Wallace, Ninemile, Mullan, and Blackwell Island (TerraGraphics et al.
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168 otn s is HHRA. ussion.
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In the Coeur d'Alene River basin HHRA, intakes were estimated in two ways, consistent with EPA guidelines for risk characterization (EPA 1995)
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Of the metals identified as potential hazards in the river basin, only arsenic was
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. Further, the committee noted ATSDR's Environmental Health Assessment in the Coeur d'Alene River basin (ATSDR 2000)
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At the Coeur d'Alene River basin site, EPA estimated cancer and noncancer health risks for both CT and RME conditions. As mentioned above, the CT estimate represents an average level of chemical exposure, while the RME is a more conservative estimate intended to be the highest exposure that can reasonably be expected to occur.
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From page 173... ...
It should also be noted that cancer risk for the 90th percentile background soil level of 22 mg/kg arsenic in the upper basin is associated with an estimated cancer risk greater than 106 using the risk assessment methodology employed in the basin.5 Modern tribal subsistence scenarios yielded cancer risk estimates similar to those for the highest nontribal residential exposures, but traditional subsistence scenarios had risks roughly 10 times higher. During visits to the river basin, the committee learned from tribal leaders that tribal members no longer practice subsistence living in the basin (CDA Resolution 42 [2001]
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EPA policy (EPA 1994) strives to reduce soil lead levels so that no child would have more than a 5% chance of exceeding a BLL of 10 micrograms per deciliter (µg/dL)
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Thus, Chapter 6 is devoted to use of the IEUBK model to understand lead exposure and uptake. The use of the model in this HHRA has projected significant risks of lead toxicity throughout the Coeur d'Alene River basin.
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However, there is a growing body of more recent evidence that environmental lead exposure is also associated with an important set of adverse health effects in adults. For example, bone lead levels that were related to lead in drinking water in Boston (Potula et al.
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. Environmental lead exposure has also been linked to elevated blood pressure and proteinuria among pregnant women (Factor-Litvak 1992)
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Increased risks of heart disease, hypertension, infection, asthma, premature delivery, and diabetes have been associated with chronic elevated stress. A particular effect of stress that may be relevant to populations with elevated lead exposure is the role of chronic stress in neurodevelopment.
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. In humans, poverty, psychological stress, and lead exposure are likely correlated, but the nature of the relationship (independence [additive toxicity]
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BLOOD LEAD STUDIES IN THE COEUR D'ALENE RIVER BASIN The Coeur d'Alene River basin HHRA included some survey data of blood lead concentrations in children, but these were sufficiently limited that the document essentially relies on the IEUBK model to predict risks from lead exposure. The limitations of the blood lead data have their
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The history of the Coeur d'Alene River basin certainly warrants evaluation of its residents as a high-risk population. An ideal lead intervention program in the Coeur d'Alene River basin would include both primary and secondary prevention strategies for exposure reduction.
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Screening is not mandatory in Idaho, and there is no evidence that physicians widely screen children in the Coeur d'Alene River basin. Therefore, these are the only data available with which to assess the prevalence of lead poisoning and to test the assumptions of the IEUBK model (see Chapter 6)
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. State health statistics did not provide a precise count of children living in the Coeur d'Alene River basin; therefore, a comprehensive census was undertaken to determine the denominator for the lead exposure survey.
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Blood Lead Studies from the River Basin The committee found it unusual that this HHRA presented aggregate data on childhood lead screening data for children aged 0-9 years (Terra
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Figure 5-3 compares the same Coeur d'Alene River basin and NHANES blood lead data among 1- to 5-year-olds when expressed as percentages of the respective populations having levels 10 µg/dL. Slightly more than 2% of the national population displayed blood lead 10 µg/dL in 1999-2000.
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substantially to declining blood lead, since cleanups were intended to first address sites posing the greatest apparent threats, and blood sampling was not random. In any case, this apparent improvement in the Coeur d'Alene River basin results was observed only after substantial remedial activity.
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Although imper fect, the Coeur d'Alene River basin blood lead data support the hypothesis that Coeur d'Alene River basin BLLs are higher than contemporaneous national BLLs.
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However, in concert with children's known tendency to ingest soil, the demonstrated (although variable) bioavailability of lead in soil in mammalian gastrointestinal tracts, and observed BLLs in children in the Coeur d'Alene River basin, they do lend support to arguments that Coeur d'Alene River basin soils represent a lead hazard to young children.
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Although the agency did not identify these as distinct sources of lead exposure, it did include any exposure that still may be associated with these sources in its risk assessment. The exposure from these sources would be found in the same places as exposure from the lead in mining wastes (for example, yard soils and house dust)
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Given the discussion above, the only contaminant in the Coeur d'Alene River basin for which such apportionment could reasonably be attempted is human exposure to lead. EPA did undertake a series of statistical analyses attempting to determine the relative effect of lead in mining wastes and lead in paint on BLLs (TerraGraphics et al.
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Public notifications, such as those posted by health departments warning residents or recreators not to eat certain fish, to wash their hands, or not to drink certain water can encourage individuals to reduce their exposures to harmful substances. During the committee's visits to Coeur d'Alene River basin area, many such public warnings were found and thought to be appropriate.
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Based on current knowledge, lowering the magnitude and duration of elevated BLLs would be expected to minimize the impact. Medical Interventions During its visits to the Coeur d'Alene River basin, the committee heard infrequent pleas from community members who believed that medications should be administered to rid the body of potentially harmful metals.
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Though there are no data concerning the impact of chelation therapy on children with lower blood lead concentrations, there is no reason to believe that the use of such drugs, which can be associated with significant adverse effects, would be effective. Thus, medical interventions with drugs that remove lead from the body do not appear to be warranted in the Coeur d'Alene River basin.
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The relevance of such studies to a Superfund site such as the Coeur d'Alene River basin is not entirely clear, since the relationship (if any) between outdoor soil and indoor dust may be different and the dynamics of lead transport may also be different.
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EPA claimed that available pre- and postremediation measurements of BLLs were supportive of EPA actions at the Coeur d'Alene River basin Superfund site. The results of cross-sectional surveys of children at the Midvale, Utah, site (the former site of a lead, zinc, and copper smelter)
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However, the activities described did not include soil replacement (although removal of slag was documented as was installation of landscaping covers like bark, chips, and grass) , so this report is not considered further here.13 The EPA experience in the Bunker Hill box at the Coeur d'Alene River basin site has also been reported (Sheldrake and Stifelman 2003; von Lindern et al.
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Indeed, the lack of any control group necessarily resulted in the methodology assigning the observed decrease in blood lead concentrations to the environmental changes caused by the interventions. Moreover, even if the reductions in BLLs observed in the box were due to the interventions, extrapolation to other locations within the Coeur d'Alene River basin may not be warranted -- for example because of differences in behaviors and opportunities for exposure within and outside the box.
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Change in surface-soil lead concentration. A reduction of 550 mg/kg ("tri mean" measure)
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"There was no evidence that blood lead levels were re duced by soil lead or dust abatement in area A There was a slight reduction (net reduction over control area of 0.6 µg/dL in Area B that may be attributed to interior dust abatement (this difference was not statistically significant)
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Overall findings "were equivocal and did not strongly support or refute a beneficial abatement effect." Other interfering effects. The concentration of air lead levels in Toronto de clined over the study period and more rapidly during 1987-1988; decreased emis sions from the smelter also may have played a part.
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In 1990-1991, all residential lots with soil lead concentration exceeding 500 mg/kg, including 80% of the 710 lots in the Notre Dame district, had soil replaced to a depth of 10 cm and then grassed or covered with gravel. Change in surface-soil lead concentration.
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Change in surface-soil lead concentration. Not stated.f Soil with lead greater than 5,000 mg/kg of lead was replaced, and assistance was provided to home owners to cover soil measuring 1,250 to 5,000 mg/kg, with only educational advice provided for lower concentrations.
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Change in surface-soil lead concentration. The decline in average "founda tion soil lead" was 488 mg/kg in the intervention group (542-54 mg/kg, a significant reduction)
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. The Bunker Hill Box at the Coeur d'Alene River Basin Superfund Site (TerraGraphics 2000; Sheldrake and Stifelman 2003; von Lindern et al.
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. both blood and soil lead levels have significantly decreased" and "There was no significant difference in mean BLLs in children continued on next page
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(2003) is especially appropriate when considering the effect of soil replacement: The outcomes of the intervention studies suggest that various approaches to intervention of the dust ingestion pathway, alone or in combination, contributed to declines in blood lead levels in children living in areas heavily contaminated with lead.
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fThis information may have been published in material not examined by the committee. gFloor dust lead and arsenic loadings and lead, but not arsenic concentrations, decreased significantly in the unremediated houses, although soil lead and arsenic concentrations did not.
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208 SUPERFUND AND MINING MEGASITES changes in blood lead in response to fluctuations in smelter emissions (Hilts 2003; Morrison 2003) 16 suggest that more attention should be paid specifically to the surface films of dust with which we come in contact rather than the larger samples generally obtained by soil sampling or vacuuming.
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ADHERENCE OF THE PROPOSED ACTIONS TO SUPERFUND GUIDANCE Summary of the Guidance The Coeur d'Alene River basin was designated as a Superfund site and listed on the National Priorities List in 1983; thus, all assessments and decisions made pertaining to the site fall under the authority of Superfund. HHRA is a key part of Superfund site cleanup.
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The existence of additional routes of exposure may account for the finding of higher than predicted BLLs in children in the lower Coeur d'Alene River basin. CONCLUSIONS AND RECOMMENDATIONS This committee was charged with examining the assessment and apportionment of risks to humans from multiple contaminant exposures related to waste site sources as well as other sources (for example, lead exposure via soil and house paint dust)
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Consequently, the HHRA is correct in concluding that environmental lead exposure poses elevated risk to the health of some Coeur d'Alene River basin residents. Conclusion 2 EPA followed guidance for determining human health risk from exposure to metals.
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However, the long-term effectiveness of this remedy in the Coeur d'Alene River basin is questionable because of the possibility, even likelihood, of recontamination. Recommendation Long-term support of institutional controls programs should be provided to avoid undue human health risks from recontamination.
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The committee agrees with relevant statements in the HHRA -- for example, that "it is clear that a subsistence-based lifestyle requires environmental lead levels orders of magnitude lower than those measured throughout the floodplain of the Coeur d'Alene River," and the conclusion that "Estimated lead intake rates for these scenarios are too high to predict BLLs with confidence. Predictions for BLLs associated with subsistence activities ...
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2000. Coeur d'Alene River Basin Environmental Health Exposure Assessment, Final Report.
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2004. Maternal stress modulates the effects of developmental lead exposure.
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1993c. Urban Soil Lead Abatement Demonstration Project.
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1994. Revised Interim Soil Lead Guidance for CERCLA Sites and RCRA Corrective Action Facilities.
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2001. Lifestyles, diets, and Native American exposure factors related to possible lead exposures and toxicity.
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1996. BLLs in Toronto children and abatement of lead-contaminated soil and house dust.
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2004. Jasper County, Missouri Superfund Site Child hood Follow-up Lead Exposure Study.
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Presentation at the First Meeting on Superfund Site Assessment and Remediation in the Coeur d'Alene River Basin, January 22, 2004, Washington, DC. Stanek, E.J.
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Presentation at the First Meeting on Superfund Site Assessment and Remediation in the Coeur d'Alene River Basin, January 22, 2004, Washington, DC. von Lindern, I., S
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