Pentachlorophenol and Cancer Risk: Stepping Out of Dioxin's Shadow (Journal Article)
Objective: Pentachlorophenol is a fungicide widely used as a wood preservative, classified in 1999 by the International Agency for Research on Cancer as a “possible human carcinogen”. We review currently available epidemiological research to determine the extent to which recent studies address the limitations of the previous data, particularly with respect to distinguishing the effect of pentachlorophenol from that of its contaminants (e.g., dioxins) and other chlorophenols. Data Sources and Extraction: We examined published studies with a quantitative or qualitative pentachlorophenol measure, or an assessment of chlorophenol exposure and additional information on specific jobs that would likely have used pentachlorophenol rather than other chlorophenols. The data collection process focused on results pertaining specifically to all cancer sites and specific hematopoietic cancers, and data pertaining to risks associated with other types of chlorophenols, dioxins, or furans. Synthesis: In contrast with dioxin, pentachlorophenol exposure was not associated with total cancer incidence or mortality. However, the pentachlorophenol studies present considerable evidence pertaining to lymphopoietic cancers, with strong associations seen in multiple studies, in different locations and using different designs. The extension of a large cohort study of sawmill workers, with follow-up to 1995, provides information about risks of relatively rare cancers (e.g., non-Hodgkin lymphoma, multiple myeloma), in a cohort with an extensive, validated exposure assessment procedure that distinguishes between pentachlorophenol and tetrachlorophenol exposures. Conclusions: The cancer risks associated with pentachlorophenol differ from those of other chlorophenols and for dioxins. Contaminant confounding is an unlikely explanation for the risks seen with pentachlorophenol exposure.