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Region 8 Libby pages

Human Health Risk Assessment

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What is a Human Health Risk Assessment?

A risk assessment is a formal, step-by-step, scientific process for quantifying health risks to residents, workers, and recreationalists. It uses standardized tools, formats, and scientifically accepted assumptions. Assessments are led by experienced toxicologists and must undergo rigorous review and scrutiny.

For much more detailed information, please visit the Region 8 Human Health Risk Assessment Web site.

Superfund risk assessments are conducted to evaluate the potential human health risks posed by uncontrolled hazardous substance sites. The process has four steps:

    1. Data collection. Provides data on site history, exposure potential, and contaminant types and distribution.
    2. Exposure assessment. Estimates how much and in what ways exposures may occur.
    3. Toxicity assessment. Addresses the potential of contaminants to cause harmful effects in humans.
    4. Risk characterization. Integrates the results of the previous steps and calculates the risk to human health if no action is taken.

Each step involves the analysis of specific data or assumptions related to the areas of contamination and potential exposure to the contamination.

Why Bother with a Risk Assessment?

People may wonder why it is necessary to conduct a risk assessment at a site where many people are reported to have died from diseases related to the primary contaminant - asbestos. To some, it seems clear that the asbestos from the Grace mine has and will continue to pose unacceptable health risks in Libby unless it is cleaned up.

However, anecdotal evidence is not enough. Site cleanups may cost tens of millions of dollars, and Superfund regulations require that EPA cleanup decisions be based on risk. These actions may be challenged in court by the Potentially Responsible Party (in this case, W.R. Grace), so they must be scientifically defensible. Also, under current law, a material must contain one percent or more asbestos to be considered an asbestos containing material, and cleanups below that limit have not been done.

Risk assessment is an ongoing process and will continue until cleanup decisions are made. In Libby, a screening level risk assessment was done under the Emergency Response Program. Although somewhat qualitative, it identified complete exposure pathways and determined if risks were high enough to warrant an immediate response. EPA used it, in conjunction with numerous other tools, to determine the next steps at the site.

As new data are collected, they will be assessed to add to the current understanding of risks at the site in a Baseline Risk Assessment. These data will help EPA answer important questions, such as:

Clearly, the risk assessment process is vital to successful site investigation and cleanup. It helps to ensure that the site cleanup will be effective in reducing the current and future risks at the site to acceptable levels.

Results of EPA's Risk Assessment for Libby, Montana

In December 2001, EPA completed a preliminary, screening level risk assessment for emergency response activities entitled Risk Assessment - Amphibole Mineral Fibers in Source Materials in Residential and Commercial Areas of Libby Pose an Imminent and Substantial Endangerment to Public Health. EPA also issued a memorandum that presented the rationale for determination of imminent and substantial endangerment to public health from asbestos contamination in various types of source materials in and around Libby. In summary, those findings are:

1. Amphibole asbestos occurs in ore and processed vermiculite from the Libby mine.

2. Asbestos fibers of this type are hazardous to humans when inhaled.

3. Asbestos fibers characteristic of those from the mine are present in many sources locally. Outdoor sources include yard and garden soil, driveway material, and mine waste materials. Indoor sources include dust and vermiculite insulation.

4. Disturbance of contaminated source materials through common activities by residents or workers can result in exposure to breathable asbestos fibers in air.

5. Concentrations of fibers in air generated by disturbance of source materials may exceed OSHA occupational exposure standards.

6. Estimated excess cancer risks caused by airborne fibers from disturbance of the material exceed EPA's acceptable risk range.

EPA concluded that source materials such as soil and soil-like media, dust, and vermiculite that contain asbestos are a likely source of ongoing release of hazardous fibers to air in Libby. In light of evidence of human asbestos exposure and the associated increase in human risk, it was recommended that EPA take appropriate steps to reduce or eliminate exposure pathways to these materials to protect area residents and workers.

The entire risk assessment can be accessed online at:

http://www.epa.gov/region8/superfund/libby/risksummary.html

 

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