Pentachlorophenol and By-products of Its Synthesis

The complex mixture pentachlorophenol and by-products of its synthesis is reasonably anticipated to be a human carcinogen based on limited evidence of carcinogenicity from studies in humans and sufficient evidence of carcinogenicity from studies in experimental animals. This conclusion is supported by mechanistic studies whose findings are consistent with the biological plausibility of its carcinogenicity in humans. Pentachlorophenol as it is used commercially is a mixture of penta chlorophenol and by-products formed or present during its production. Pentachlorophenol and by-products of its synthesis (hereinafter referred to collectively as “pentachlorophenol”) includes higher-chlorinated dioxins and furans, polychlorinated phenols, hexachloro benzene, and other by-products specified below, under Properties. People exposed to pentachlorophenol are also exposed to its by-products; therefore, the listing is for this complex mixture. The epidemiological studies could not separate the effects of pentachlorophenol from any effects of its by-products. Dioxin (specifically 2,3,7,8-tetrachlorodibenzo-p-dioxin [2,3,7,8-TCDD]) (Cogliano et al. 2011) has been associated with non-Hodgkin lymphoma (NHL) in humans, and it is plausible that dioxin-like activity of the by-products may have contributed to the NHL observed in the epidemiological studies of workers exposed to pentachlorophenol. Also, the evidence from studies in experimental animals indicates that the observed carcinogenicity cannot be fully explained by either the presence of by-products alone or pentachlorophenol alone.