HSIA representatives expressed "extreme disappointment" in the US Environmental Protection Agency’s (EPA) draft toxicity assessment for perchloroethylene at a ‘listening session’ held by the Agency in mid August. The assessment "seems to take at face value studies that show an association between perchloroethylene and adverse effects and to disregard studies that show no such effects," according to HSIA Counsel W. Caffey Norman. The result is a series of harsh conclusions "that are not supported by the evidence" and that are "not founded in accepted scientific practices or . . . EPA’s stated policies," according to the Alliance’s Director of Scientific Affairs, Dr. Paul Dugard.

The listening session was scheduled by EPA to provide the interested public with an opportunity to offer preliminary thoughts on the draft assessment. The draft assessment was released in late June and is intended to update information on perchloroethylene in EPA’s Integrated Risk Information System (IRIS). Written comments are due on the 500-page draft by September 24.

In his comments, HSIA Counsel Caffey Norman criticized the draft for its lack of a rigorous application of EPA’s cancer guidelines. He noted that the draft puts as much, or greater, weight on community drinking water studies with poorly characterized exposures that suggest a cancer link as it does on the conclusions of most independent reviewers that human studies do not constitute evidence for an increased risk of cancer resulting from exposure to perchloroethylene.

Mr. Norman contrasted the conclusions of the EPA draft concerning the human cancer evidence with the perchloroethylene assessment recently approved by the European Commission’s (EC) Scientific Committee of Health and Environmental Risks of the Health and Consumer Protection Directorate General. In reviewing the cancer incidence studies, the EC assessment concludes that "no increases in risks from exposure to [perchloroethylene] for any specific type of cancer, including risks from liver and renal cancers, have been observed."

In particular the European assessment discounts the community drinking water studies on which EPA places significant weight in deriving its draft conclusion that perchloroethylene is "likely to be carcinogenic to humans." The EC assessment notes that the nature of the exposures described in the drinking water studies conducted in the Cape Cod region of Massachusetts is such that there is considerable uncertainty concerning the levels to which subjects of the studies were actually exposed. "The estimated relative delivered dose, taken in over many years in drinking water, are typically less than would be inhaled in one shift in a dry cleaning shop working well within the occupational exposure limit," the European assessment points out.

Mr. Norman also expressed concern that EPA discounted the results from the most careful possible examination of existing worker populations, funded by HSIA and the Danish Medical Research Council, completed in 2006. The study of drycleaning workers in the four Nordic countries (Lynge et al, 2006) is dismissed in the EPA draft assessment as "null and informative." The HSIA Counsel expressed dismay that the Agency "could discount such a carefully designed study, based on ‘potential biases,’ while emphasizing the results of lesser quality community drinking water studies of mixed solvent exposure."

Focusing mainly on draft’s evaluation of the animal data, Dr. Paul Dugard commented that EPA’s use of the occurrence of mononuclear cell leukemia in laboratory rats as a basis for quantitative risk assessment in humans is inappropriate. Dr. Dugard pointed out that EPA’s own data indicate that the model the Agency used overestimates perchloroethylene metabolism at low doses, in some cases by more than ten-fold.

Release of the IRIS draft was reportedly delayed nearly 2 years because of disagreements within the Agency over how to assess the chemical’s cancer risks and how to present the scientific uncertainty about those risks.  Following the close of the public comment period in late September, the draft perchloroethylene assessment will be reviewed by a panel of experts convened by the National Academy of Sciences (NAS). The panel’s review is expected to take 15 months to complete.

In summing up his comments, Mr. Norman suggested that the EPA draft lacks the careful application of scientific judgment and synthesis required by Agency guidelines. He urged EPA to make revisions before the draft is sent to NAS. He cautioned that EPA risks significant delays in the review process if it chooses to send a "dog’s breakfast" like the current draft over to the Academy for review. [He later described a dog’s breakfast as "a disorderly mixture or hodgepodge."]