What is a risk assessment and what does it tell us?
The Environmental Protection Agency hopes to announce the final toxicity values for Libby Amphibole asbestos later this fall. This information will allow us to assign a numeric value to risk levels associated with different activities. The agency expects to complete a risk assessment within six months of releasing the toxicity values.
The two toxicity values are the cancer value, an estimate of the potential for cancer health effects (mesothelioma and lung cancer) from exposure to Libby Amphibole asbestos, and the non-cancer value, an estimate of the potential for non-cancer health effects (asbestosis and pleural thickening) from exposure.
The Human Health Risk Assessment will help support decisions for the site and will provide answers to three basic questions: what hazardous substances are you exposed to and how toxic are they? Is there risk from exposure? Have we cleaned up enough?
The question of what hazardous substance is associated with the Libby Site is straightforward: Libby Amphibole Asbestos. As you are aware, hundreds of residents have been exposed to excessive amounts of this contaminant as a result of working in the vermiculite mine and processing facilities, and using vermiculite contaminated with asbestos in homes and yards.
Many have asked if Libby Amphibole asbestos is significantly more toxic than other types of asbestos and why have so many people contracted asbestos-related disease in Libby and Troy? Our investigations in Libby and Troy have shown that this form of asbestos may not be more toxic, but there has been a higher level of exposure in comparison to other places in the United States where one might come into contact with asbestos. This is because concentrations at the site have been higher and because there have been more ways for community members to come into contact with Libby Amphibole asbestos.
When the mine and processing facilities were in operation, the concentration of asbestos in the air in Libby was at times between one million and 10 million fibers per meter cubed. A meter cubed is about the size of a washing machine. Today, concentrations in Libby are between about one and four fibers per meter cubed, about the same as what you find in Helena and Eureka. This is because the mine and processing facilities are no longer in operation and because the Environmental Protection Agency has removed more than a million tons of contaminated soil from yards, schools and businesses. The risk assessment will allow us to guide community members on risks associated with particular activities in and around the Superfund site.
Finally, the risk assessment will help us determine whether enough cleanup has been conducted. We have collected thousands of samples to better understand exposures in Libby and Troy. The final risk assessment will look at air and soil exposures before and after removal actions to determine if the exposures have been reduced sufficiently and to determine if the remaining exposures and resultant risks are within agency cleanup targets.
If the human health risk assessment demonstrates that excessive risk remains, action will be required. The agency expects to complete a feasibility study and proposed plan early in 2015 that will document the variety of possible actions and the preferred remedy option. We look forward to intensive input from the community during this time period since community acceptance is one of nine criteria used in selecting a final remedy.
In the meantime, we look forward to answering any questions you may have about the forthcoming toxicity values and human health risk assessment.
— Dr. Deborah McKean is the lead toxicologist and supervisor of the EPA’s
Region 8 Libby Team