Bertazzi et al. Respond to Smith and Lopipero

We thank Smith and Lopipero for their invited commentary (1), which we found appropriate and useful for interpreting the latest Seveso, Italy, findings (2). Human exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is widespread (3). Epidemiologic studies are essential to assessing the risk linked to the environmental contamination, and consistency in the findings enhances confidence in their results. It is not surprising that, on average, exposure to TCDD in Seveso was lower than in occupational cohorts. In the former case, the chemical release was limited in time, and its content eventually was diluted over an extended outdoor area (4). Still, the average TCDD blood concentration in the Seveso population was two orders of magnitude higher than the reported background environmental level (1). Thus, the finding of increased cancer mortality cannot be considered totally unexpected. An increase in all-cancer and lung cancer mortality, consistent with what was observed in occupational cohorts, was found in men in zones A and B after 15 years. Smith and Lopipero (1) suggest that smoking might be the actual explanation. This is a possibility, and we intend to further explore smoking habits in our index and referent populations.