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OEHHA Lists Pentachlorophenol and By-products

OEHHA Lists Pentachlorophenol and By-products

Author: Jack Schatz/Friday, October 21, 2016/Categories: California Law and Regulation, CalEPA, OEHHA, Prop65, Regulatory Proposals, US EPA, National Toxicology Program (NTP)

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California’s Office of Environmental Health Hazard Assessment (OEHHA) today added pentachlorophenol and by-products of its synthesis (complex mixture) to the Proposition 65 list of chemicals known to the state to cause cancer.  

The listing became effective with its announcement. 

Enforcement of alleged violations of a failure to warn about pentachlorophenol and by-products of its synthesis (complex mixture) will commence on October 21, 2017.

The listing of pentachlorophenol and by-products of its synthesis (complex mixture) is based on the formal identification by the National Toxicology Program (NTP) that the chemical causes cancer.

In 2014, NTP published the 13th Edition of the Report on Carcinogens (ROC).  This report satisfies the formal identification and sufficiency of evidence criteria in the Proposition 65 regulations for pentachlorophenol and by‑products of its synthesis (complex mixture). NTP concluded that “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” Additionally, NTP states that “People exposed to pentachlorophenol are also exposed to its by‑products; therefore, the listing is for this complex mixture,” and that “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.”

OEHHA is relied on NTP’s discussion of data and conclusions in the report that pentachlorophenol and by‑products of its synthesis (complex mixture) causes cancer. Evidence described in the report includes studies showing that pentachlorophenol and by‑products of its synthesis (complex mixture) increased the incidences of malignant liver tumors in male mice, combined malignant and benign liver tumors and combined malignant and benign adrenal-gland tumors in male and female mice, malignant tumors of the blood vessels of the spleen and/or liver in female mice, malignant tumors in the tunica vaginalis of the testes in male rats, and malignant tumors of the nose to an unusual degree with respect to tumor type in male rats.

The chemical pentachlorophenol has been listed under Proposition 65 as known to cause cancer since January 1, 1990.  This listing pertains to the complex mixture containing both pentachlorophenol and one or more compounds formed as by-products of pentachlorophenol synthesis.

Public comments submitted by the Pentachlorophenol Task Force last December note that “pentachlorophenol and by‑products of its synthesis is nothing more than the form of pentachlorophenol (technical grade) that is registered with the U.S. EPA as a wood preservative and is the form of pentachlorophenol to which persons in the State of California would potentially be exposed.  There is no other article of commerce that contains pentachlorophenol,” the task force wrote.

The task force notes that by products associated with carcinogenicity, principally: Polychlorinated dibenzo-p-dioxins, Polychlorinated dibenzofurans and Hexachlorobenzene are already listed as carcinogens under Proposition 65.  

The task force concluded that “a separate listing of pentachlorophenol and by‑products of its synthesis would be duplicative and unnecessary.”



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Jack Schatz

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