The peer review panel of nine independent scientists met May 12 to discuss USEPA’s draft IRIS Toxicological Review of Hexavalent Chromium. Support was expressed for USEPA to consider the forthcoming results of the Cr-VI Mode of Action (MOA) research project funded by the American Chemistry Council. This research project addresses data gaps from the 2008 National Toxicology Program (NTP) Cr-VI chronic bioassay drinking water study. The 2008 NTP bioassay was used by the agency to set the oral reference dose (RfD) for Cr-VI carcinogenicity in the draft document.
Peer review panel members discussed USEPA’s use of a linear low-dose extrapolation model for assessing Cr-VI cancer risk. Serious concerns were raised regarding this approach. Cr-VI toxicity and carcinogenicity exhibits threshold mechanisms in the human system and gut and also demonstrates non-linearity. In addition, many panel members do not believe the scientific evidence supports a mutagenic MOA for Cr-VI proposed in the draft IRIS Review.
Panel members recommended that draft document be reorganized and edited. The panel is expected to submit its final comments to USEPA in the coming weeks. Although USEPA staff said the agency will seriously consider the peer reviewers’ comments, the agency is not obligated to adopt or agree with them.