The U.S. EPA’s new cancer risk guidance addresses for the first time the likelihood that children are more susceptible than adults to mutagenic carcinogens. The final guidance, issued in March, also clarifies recommendations for assessing carcinogens that do not cause cancer below a threshold dose. Scientists from EPA, states, and industry will use the guidance when they perform risk assessments on chemicals.
The final guidance is similar to what the agency proposed two years ago (Environ. Sci. Technol. 2003, 37, 204A). For mutagenic chemicals that cause cancer, EPA estimates that exposures to children less than 2 years old are 10 times as risky as adult exposures. Exposures when children are 216 are 3 times as risky, and exposures over the age of 16 pose no additional risk compared with adult exposures. In previous guidance, childhood exposure was treated as equally risky as adult exposure.
The additional risk factors applied to children’s exposure could have a major impact on water-quality regulations for mutagenic chemicals, according to toxicologist Erin Snyder, with engineering consultants Black & Veatch. For example, if disinfection byproducts were regulated on the basis of mutagenicity in early life stages, then the regulations could become more stringent, she explained at a meeting in Baltimore on the guidelines, sponsored by the International Society of Regulatory Toxicology and Pharmacology. Other speakers suggested that the guidelines could also result in more expensive contaminated-site cleanups but would not have a dramatic impact on pesticide regulations or air-quality regulations because most of the chemicals that fall under these regulations are not mutagens.
For chemicals that are not mutagenic and for which the mechanism of action is understood, the guidelines make it clear that the agency will favor data analysis over default assumptions, according to EPA Acting Deputy Administrator William Farland. For example, chloroform doesn’t cause cancer below a threshold dose in rats and mice, so the data wouldn’t support an analysis that attributed risk to doses below the threshold. Default assumptions are numerical values that the agency uses when data are uncertain or missing.
A new section in the final guidance allows industries to call for “expert elicitation”, a provision that could lengthen an already long evaluation of cancer-causing chemicals, according to the environmental group Natural Resources Defense Council. Expert elicitation requires that the views of experts be formally polled before a standard is finalized.
The cancer guidelines and supplemental guidance are available at:
http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=116283. Information about the workshop on risk from exposure at early life stages can be found at: