In addition to considering any data gaps involving these five studies, the risk assessor should as is now standard Agency practice evaluate other data gaps, particularly those that pertain to evaluating risk to children and other sensitive subpopulations.

However, EPA (2002b) continued that when determining the need for a database UF, the risk assessor should evaluate how likely the missing or inadequate study will substantially change the outcome of the overall risk assessment. EPA (2002a) found that when the traditional UFs are appropriately applied, they are usually adequate and that an additional factor, such as an FQPA factor, was not needed to address concerns regarding prenatal and postnatal toxicity.

EPA (2002b) is considering new studies and modification of existing guideline studies to provide a more comprehensive coverage of life stages, a more systematic evaluation of pharmacokinetics, and a more focused evaluation of structural and functional toxicity in the young. Such studies might include pharmacokinetics in fetuses or young animals, direct dosing of offspring before weaning, enhanced developmental-neurotoxicity studies, developmental-immunotoxicity studies, and enhanced evaluations related to endocrine disruption.

CANCER RISK-ASSESSMENT GUIDANCE

Principles for assessing cancer hazards and risks have been in use at least since the early 1970s (OTA 1987). In the early 1980s, NRC recommended periodic updating of risk-assessment guidelines to keep pace with scientific advances and to clarify science policy positions (NRC 1983). Several agencies and organizations have developed and implemented guidelines or principles for cancer risk assessment. EPA (1986, 1996b, 1999, 2005a) has developed, revised, and conducted peer reviews of its cancer risk-assessment guidelines over the years as the scientific basis of evaluation has evolved. The current EPA (2005a) carcinogen guidelines emphasize cancer hazard identification and dose-response assessment and provide limited guidance for carcinogen exposure assessment and risk characterization. EPA (2005b) has also published supplemental guidelines to describe possible approaches for assessing risks resulting from early-in-life exposures to carcinogens.



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