Testing the validity of a proposed dermal cancer slope factor for Benzo[a]pyrene

In 2014, the United States Environmental Protection Agency (EPA) proposed a Dermal Slope Factor (DSF) for benzo[a]pyrene (BaP) of 0.006 (μg/day)-1 (USEPA 2014a). It would make cancer risk estimates associated with soil contact 100 times greater than those from soil ingestion and would predict that a large fraction of skin Basal Cell Carcinomas (BCCs) and Squamous Cell Carcinomas (SCCs) worldwide are caused by low level dermal exposures to PAHs, such as BaP. This is not logical given that sunlight (ultraviolet radiation (UV)) exposure is the generally recognized cause of BCCs and SCCs. This paper critically evaluates the proposed DSF. First, a reality check is performed using EPA standard risk assessment methods and comparing the results to actual BCC and SCC rates in the U.S. population. Then, the biological plausibility of the mechanism by which PAHs might cause human skin cancer is evaluated by exploring the generally recognized etiology of human skin cancer and comparing the genetic mutation signatures of rodent skin tumors caused by PAH exposures to those of human skin cancers. It is concluded that scientific flaws resulted in a proposed DSF value that greatly overestimates the skin cancer risk for humans dermally exposed to BaP in soil. •USEPA's proposed Dermal Slope Factor (DSF) vastly overestimates the risk of skin cancer from contact with benzo(a)pyrene.•The DSF predicts that benzo(a)pyrene in soil would exceed sunlight as the major cause of human skin cancer.•There is no plausible biological mechanism for benzo(a)pyrene to be the major cause of human skin cancer.•Human skin tumors contain high levels of UV-signature mutations, not polycyclic aromatic hydrocarbon signature mutations.