Kathryn St. John (202) 249-6513
September 30, 2010

Agency Acts Prematurely, Choosing Not to Wait for Results of Upcoming Study

WASHINGTON, D.C. (September 30, 2010) - In today's Federal Register, the U.S. Environmental Protection Agency (EPA) issued a call for public comment on hexavalent chromium IRIS risk assessment. The following statement regarding this action may be attributed to ACC Senior Director, Ann Mason:

"ACC supports a comprehensive risk assessment of hexavalent chromium Cr(VI) to ensure that any health risk posed by exposure is assessed as accurately as possible and is based on the best available science. But, today EPA issued its draft IRIS health risk assessment, after recently shortening the previously-announced timetable, rather than waiting for additional data that the agency knows is being developed. These new data, to be released by early 2011, could provide a more robust scientific basis to the cancer risk assessment.

"It is unclear why EPA feels it necessary to act now, rather than wait to review the Cr(VI) studies underway, some of which have already been released for peer review. These studies are needed to provide EPA with additional important data and "˜the best available peer-reviewed science' on any potential effects of Cr(VI) on human health."

A bout Hexavalent Chromium and the IRIS Process

Hexavalent chromium is a compound used to create pigments and prevent corrosion in dyes, paints, primers, inks, and plastics. Chromic acid is also electroplated onto metals to create shiny decorative and protective coatings.

Based on tumor results of 2008 National Toxicology Program (NTP) studies, data gaps in the Cr(VI) mode(s) of action were identified that are essential to conducting a risk assessment consistent with the  U.S. EPA Guidelines for Carcinogen Risk Assessment (2005).  To address those essential data needs, the ACC Hexavalent Chromium Panel engaged Toxicology Excellence for Risk Assessment (TERA), an independent, authoritative scientific organization, to convene a Science Advisory Board (SAB). As a result of the July 2009 SAB meeting, the research is in various stages of development at distinguished laboratories including Southern Research Institute (where the NTP study was performed) and Michigan State University.

Research has been focused on five key areas that will help identify the mode of action (MOA) for Cr(VI):1) a 90-day drinking water study; 2) genomic studies on tissues from the 90-day study; 3) pharmacokinetic modeling; 4) in vivo mutation analysis; and 5) high data content in vitro studies.

The Panel believes that these key data now being independently developed would result in a more robust cancer risk assessment for Cr(VI). Nonetheless, EPA has indicated it will rely on the 2008 NTP studies, which included some significant new findings, but these were limited to the rodents' intake of high concentrations of Cr(VI) in their drinking water. The study found that, at these high concentrations, Cr(VI) could cause tumors in rats and mice, which had not been observed before. However, the very high concentrations of Cr(VI) used in the study of rodents raise questions about the relevance of the NTP findings to humans, whose normal exposures are much lower. In fact, the concentrations of Cr(VI) in the rodents' drinking water far exceeded typical human environmental exposures, and were so large that normal protective mechanisms in the rodents were likely overwhelmed.

The NTP study also lacked MOA information, which would make clear the role of Cr(VI) in tumor development. Including these new data would also have alleviated some of the uncertainty in applying the study's results to humans. EPA should recognize the limitations of the NTP study and seek additional research to better understand the relevance of these rodent laboratory studies to environmental exposures of Cr(VI) to humans.


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