A 17-member panel of scientists will begin a peer review process this month of the Environmental
Protection Agency’s draft risk assessment for perchloroethylene.
The review is expected to take about 15 months. Comments from the review panel,
which is comprised mainly of university scientists, along with input from the
public in a comment period that ended last month, will be used by EPA to update
information on perc for its Integrated Risk Assessment System (IRIS). IRIS, a
database of human health effects that could be caused by exposure to various
substances, is used in decision-making and regulatory activities. As such it
could have far-reaching ramifications for future regulation of the drycleaning
solvent.
The risk assessment addresses potential cancer and non-cancer human health
effects of perc exposure. The draft suggests that perc should be considered a
likely human carcinogen, which would place it in the second highest of five
categories under EPA’s cancer assessment guidelines, between the highest risk category “carcinogenic to humans,” and the third highest “suggestive evidence of carcinogenic approval.”
That would represent an elevation of EPA’s official evaluation of perc’s cancer risk in which perc is considered in between a “possible” and “probable” cancer risk.
EPA released the draft document last summer, opening it for a 90-day period of public comments that ended in September. Most of the comments received were critical of aspects
of the 500-page document, disagreeing with how EPA weighed and evaluated the
many studies of the effects of perc exposure.
The Coalition for Effective Environment Information noted that “there is disagreement among experts, including other governmental agencies, on
some of the critical issues in the assessment.”
CEEI, which includes representatives from the aerospace, chemical, automobile,
pharmaceutical, petroleum, electronics and consumer products industries, noted
that a recent European Union commission study “evaluated essentially the same data set as EPA considered but reached scientific
conclusions that are substantially different from what is presented in the perc
assessment.”
The EU study, which has already been peer reviewed, concluded that no further
testing or risk reduction measures are needed concerning consumer exposures to
perc.
CEEI also urged EPA to consider how the public perceives the hazard descriptions
that the agency uses.
“In using the phrase ‘likely to be carcinogenic it humans’ to communicate a weight of evidence concept, EPA is using language that is
easily misunderstood. The term ‘likely’ in this context is naturally interpreted to mean that there is a high
probability that a person exposed to a chemical carrying the label would get
cancer. EPA has an important obligation to communicate to the public what is
intended by the use of this term in a weight of evidence context.”
Since “likely” as used in the EPA context does not equate to the common understanding of the
word, EPA instead should articulate what the label actually means.
Other commenters criticized how EPA weighed the various studies of perc in
coming to its conclusions.
The Air Force Center for Engineering and Environment said the draft “contains many internal contradictions and relies heavily on speculation rather
than hard evidence.”
Studies were included “without consideration of their quality or appropriateness for assessing human
health risks,” the center said, and the EPA “used epidemiologic and animal data selectively and, in some cases, have
misrepresented those data.”
The Alliance for Environmental Responsibility (AERO), which is sponsored by the
Aerospace Industries Association, criticized EPA for taking “at face value those studies that show an association between perc and adverse
effects, and disregarding or discounting studies that do not show effects.
“There is no indication that EPA consistently applied a defined set of
scientifically sound criteria to evaluate the studies cited in the Draft
Assessment, to select or reject specific studies for inclusion in the analysis,
or to determine the ‘weight of the evidence.’ It is often impossible to tell whether EPA’s reliance upon, or rejection of, a study is scientifically appropriate.”
By far the most extensive comments were submitted by the Halogenated Solvents
Industry Alliance (HSIA), which represents equipment manufacturers, and producers, distributors, and commercial users of
perc and other halogenated solvents.
Dr. Paul H. Dugard, director of scientific programs for HSIA, said the draft
failed to conduct an objective and comprehensive assessment of the relevant
studies in humans and laboratory animals. Several recent publications
specifically designed to answer questions raised in earlier studies were
disregarded, HSIA said.
The primary difference between the European Union study and EPA’s draft, HSIA said, is that EU report “recognizes the limitations of the mixed solvent community drinking water studies
on which EPA appears to place equal weight to the cohort studies.”
Dugard also complained that EPA discounted a study designed “expressly to answer the key questions posed by the extensive epidemiologic
database: why were increased esophageal cancers observed in
perchloroethylene-only subcohorts studied by the National Institute for
Occupational Safety and Heath and the National Cancer Institute, but not in
other studies?”
The study Dugard refers to covered drycleaning plant workers in several Nordic
countries and was completed in 2006. That study, according to HSIA, was the
first to compare cancer incidence among exposed workers with those in a similar
socioeconomic group (i.e. laundry workers) and represented the largest group of
drycleaning workers ever studied.
In a separate comment, one of the authors of that study, Elizabeth Lynge of the
Institute of Public Health at the University of Copenhagen, said the
characterization of the study presented in the EPA draft was “scientifically misleading.”
“It seems that the EPA reviewers have not fully understood the design of the
Nordic study,” she wrote.
While most of the public comments were critical of the EPA draft, the agency did
get support from its efforts from officials in two states — Massachusetts and New York.
Issues raised by the commenters should be addressed by the peer review panel
which was scheduled to begin its work this month. The panel will issue a report
at the end of the process, probably in early 2010, but it will not be
developing its own risk characterization or addressing risk management issues.
• Does the hazard characterization of perc provide a scientifically-balanced,
objective, and complete description that synthesizes the animal, clinical, and
epidemiologic evidence for toxicity?
• Do the available data support the hypothesis that multiple modes of action may
contribute to carcinogenesis following exposure to perc?
• Have the scientific uncertainties in the database been identified and clearly
articulated?
