EPA closes in on Libby toxicity value

An important step in the development of a risk assessment for Libby’s unique form of asbestos is almost complete, Environmental Protection Agency officials told the Libby City Council at a presentation Tuesday.

“We anticipate Libby-specific toxicity values may be available in April this year,” EPA toxicologist David Berry said.

Libby amphibole asbestos is believed by scientists to be more potent than that of the more common chrysotile asbestos, though science has yet to determine conclusively to what degree.

The EPA’s toxicity assessment will determine the relationship between the dose of Libby amphibole and its biological response – for both cancer effects and non-cancer effects – Berry said. Though animal studies were used, he added, the bulk of data was taken from human epidemiology studies.

Data from Libby vermiculite miners helped develop toxicity factors for cancer effects, while the non-cancer value was based on workers who processed Libby vermiculite at a plant in Marysville, Ohio.

The values will be peer-reviewed internally, Berry said. Afterward, an external scientific advisory board will look over the data and science behind the values, and provide comments. The document will be available to the public at that point, he said.

Councilmember D.C. Orr expressed concern that the internal review may be more of a political conversation than a scientific one, as was the case in determining whether to declare the Libby-area Superfund site a public health emergency. Councilmember Vicky Lawrence asked how accurate the values would be considering that some numbers must be computed using models and assumptions.

“The agency has been working very hard developing those factors,” Berry replied. “It is hoped that the external peer review will provide critical comment if there are any flaws in EPA’s logic or the models that are used.”

Victor Ketellapper, EPA’s Libby team leader, also pointed out that when EPA deals with indefinite data, such as when handling a range of values, the agency uses the most conservative number in order to be most protective of human health.

“The way the EPA deals with uncertainties in developing toxicity value and throughout the risk assessment itself is they always err on the side of being conservative,” he said.

For the past decade and to the disapproval of EPA’s critics, the agency has relied upon the toxicity values of chrysotile in determining the risk associated with contamination in Libby.

With new data that will most-likely reveal Libby amphibole is more potent, councilmembers wanted to know what that would mean for cleanup work that has already been complete. EPA officials say that they plan to re-evaluate the risk assessment and remedies and then act accordingly.

“I think we would look at the remedy we are implementing at the residential properties right now and determine if there is additional work that needs to be done,” Ketellapper said, “or evaluate if the remedy that we’re doing now is protective.”

The EPA and Libby City Council have yet to agree on a specific clean-up solution for Riverfront Park, or Operable Unit 1. Some have argued that they want to wait until the new risk assessment comes out before performing remediation at the park, but the EPA asserts that no matter what the toxicity value is, it is high enough that the exposure path should be broken as soon as possible. 

Berry said that though the remedy will be carried out before the new risk assessment is issued, the EPA has agreed to perform more testing afterward to ensure the remedy’s effectiveness.

“One of the things that EPA is committed to doing after they have conducted the remedial action of OU1 is to do additional, confirmatory activity-based sampling,” Berry said, “and then we will use the new toxicity values to evaluate the theoretical risks.”