EWG response to EPA’s review of chromium-6 health effects


Office of Environmental Information (OEI)

Docket Mail Code: 2822T

U.S. Environmental Protection Agency

1200 Pennsylvania Ave., NW.

Washington, DC 20460

Re: Docket ID No. EPA-HQ-ORD-2010-0540

To Whom It May Concern: Environmental Working Group is a non-profit public health, environmental research and advocacy organization based in Washington, DC, with offices in Ames, Iowa and Oakland, Calif. We focus much of our research on potential health risks from exposures to hazardous chemicals that contaminate food, water and the environment or that are used as ingredients in consumer products. With this letter, we offer detailed feedback to the U.S. Environmental Protection Agency regarding its draft “Toxicological Review of Hexavalent Chromium: In Support of Summary Information on the Integrated Risk Information System (IRIS).”

We commend EPA’s recent steps to assess the health effects linked to hexavalent chromium in drinking water and have undertaken a detailed examination of the draft document. We find the EPA’s toxicological review to be a thorough discussion of a wealth of data concerning hexavalent chromium chemistry and toxicology. There is no need to extend the comment period, weaken the conclusions or delay finalization of this document. We wish to emphasize three additional points to agency staff:

  1. There is sufficient evidence that hexavalent chromium causes cancer through a mutagenic mode of action, such that the EPA’s use of strict linear modeling is appropriate for risk assessment.
  2. A re-analysis of National Toxicology Program (NTP) cancer data may be necessary to account for study animals whose organs were harvested but not assessed for tumors, as indicated by the staff of California’s Office of Environmental Health Hazard Assessment (OEHHA).
  3. Since hexavalent chromium is already classified as a known human carcinogen via inhalation and, according to this draft document, a likely human carcinogen via oral exposure, EPA must consider it to be a known human carcinogen.

Chromium-6 causes cancer through mutation The EPA draft toxicological review provides substantial evidence of hexavalent chromium’s mutagenic mode of action. This conclusion is consistent with the state of California’s draft public health goal for the contaminant (OEHHA 2009). It is further supported by an independent, peerreviewed publication by EPA scientists that documents an analysis of chromium-6 data using the agency’s draft framework for assessing mutagens (McCarroll 2010). It is essential therefore that EPA retain the additional 10-fold safety factor for children in its cancer risk derivation. While future studies may suggest that hexavalent chromium can cause cancer through other mechanisms as well, its well-documented mutagenic properties require the EPA to use strict linear modeling in assessing cancer risk. The state of California now applies “children’s cancer potency factors” to all carcinogenic chemicals, not just mutagens. The agency made a sound, scientifically defensible decision in using linear modeling in the draft toxicological review.

Correct use of NTP tumor data may indicate higher cancer risk Comments submitted by the California’s Health Hazard office prior to public dissemination of EPA’s draft document noted that the incidence of adenomas or carcinomas reported in Tables 5-5 and 5-6 are incorrect in some cases, and analysis based on these values is therefore also incorrect (OEHHA 2010). The denominators used do not exclude animals whose organs could not be assessed for tumors due to autolysis, nor do they exclude control animals that died well before the conclusion of the study. The EPA must adjust its evaluation of adenoma and carcinoma incidence documented in the NTP study and alter its risk calculations accordingly. Proper assessment of tumor incidence may well reveal an increased risk associated with exposure to hexavalent chromium in drinking water.

Chromium-6: A known human carcinogen In its weight-of-evidence characterization of the carcinogenicity of hexavalent chromium over all exposure pathways, the EPA must conclude that the chemical is a known human carcinogen. The agency previously established that the chemical is a known human carcinogen when exposure occurs via inhalation (EPA 1998). Based on this draft document, the EPA considers hexavalent chromium to be a likely human carcinogen via the oral route of exposure as well. A health-protective weight-of-evidence evaluation considering both exposure pathways should therefore lead to the conclusion that chromium-6 is a known human carcinogen. We thank the EPA for the opportunity to comment on this draft toxicological assessment and urge the agency to finalize its draft without delay. This common drinking water contaminant poses a serious threat to the health of Americans, and adoption of a new drinking water regulation depends on speedy resolution of the IRIS process. Sincerely,

Rebecca Sutton, Ph.D. Senior Scientist

Environmental Working Group

1436 U St. NW, Suite 100

Washington, DC 20009


EPA (Environmental Protection Agency). 1998. Toxicological Review of Hexavalent Chromium (CAS No. 18540-29-9). August 1998. Available at:

McCarroll N, Keshava N, Chen J, Akerman G, Kligerman A, Rinde E. 2010. An evaluation of the mode of action framework for mutagenic carcinogens case study II: chromium (VI). Environmental and Molecular Mutagenesis 51(2): 89-111.

OEHHA (Office of Environmental Health Hazard Assessment). 2009. Draft Public Health Goal for Hexavalent Chromium in Drinking Water: Pesticide and Environmental Toxicology Branch, Office of Environmental Health Hazard Assessment, California Environmental Protection Agency. Available at:

OEHHA (Office of Environmental Health Hazard Assessment). 2010. Comments on: EPA’s Toxicological Review of Hexavalent Chromium, EPA/635/R-10/004A. May 26, 2010.