No Significant Risk Levels (nsrls) for the Proposition 65 Carcinogens Benzo[b]fluoranthene, Benzo[j]fluoranthene, Chrysene, Di

The oral cancer potencies of six polycyclic aromatic hydrocarbons (benzo[b]fluoranthene, benzo[j]fluoranthene, chrysene, dibenzo[a,h]pyrene, dibenzo[a,i]pyrene, and 5-methylchrysene) were estimated from cancer dose-response data obtained from animal studies. Potency estimates obtained from newborn mouse intraperitoneal (i.p.) injection studies were converted to oral equivalent potencies. The conversions were based on data for benzo[a]pyrene for which both oral adult mouse data and i.p. newborn mouse data are available. Benzo[a]pyrene is 75 times more potent in newborn mouse i.p. studies than in adult oral studies. Therefore, to obtain oral potency estimates, the potencies estimated from the newborn mouse i.p. studies for these six polycyclic aromatic hydrocarbons were adjusted downward by a factor of 75. Differences in potencies between the oral and newborn i.p. studies is likely to be due to pharmacokinetic differences from different routes of administration and greater sensitivity of the neonatal mice relative to the adult mice. Risks from perinatal PAH exposure may be underestimated by the potencies presented here because exposures early in life can result in greater cancer risks than exposures occurring in adulthood and studies of adult oral benzo[a]pyrene were used in developing the adjustment factor employed here.