Screening-level population risk assessment of nasal tumors in the US due to naphthalene exposure

Several naphthalene Unit Risk Factors (URFs) were proposed by the US Environmental Protection Agency in 2004 using data on the development of olfactory epithelial neuroblastomas and nasal respiratory epithelial adenomas in rats, but these URFs may be inappropriate and unnecessarily conservative for estimating human cancer risks. The purpose of the present exercise was to perform a screening-level population risk assessment of the US population to compare the observed number of naphthalene-induced nasal tumors in the US to the number that would be predicted if the URFs for naphthalene were as proposed. Nine scenarios were evaluated to represent the range of exposures individuals have typically experienced. Results indicate that the total predicted burden of naphthalene-induced nasal tumors per year in the US (65,905 rare nasal tumors, of which 29,121 are olfactory epithelial neuroblastomas) is much greater than the number of these tumors actually observed per year (910 total nasal tumors, of which 66 are olfactory neuroblastomas) over the period 1973-2006. This suggests that using rat nasal tumor data to derive a naphthalene URF for humans should be re-evaluated.