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Gradient Scientists Find Styrene's Listing in the 12th Report on Carcinogens Not Supported by the Science


An analysis conducted by Gradient scientists contends studies in humans, and particularly workers with high styrene exposures, show no consistent increase in death from any type of cancer.

The summary by Lorenz Rhomberg, Ph.D., FATS, Julie Goodman Ph.D., DABT, and Robyn Prueitt, Ph.D. of an independent weight-of-evidence analysis assessing whether styrene should be considered a human carcinogen has been published in the January/February 2013 issue of Human and Ecological Risk Assessment, a peer-reviewed scientific journal.

“The only known plausible biological mechanism by which styrene could cause cancer is specific to the mouse lung and not relevant to humans,” states Rhomberg.

The Gradient analysis contradicts the National Toxicology Program's (NTP) listing of styrene as “reasonably anticipated” to be a human carcinogen in its 12th Report on Carcinogens (RoC), published in June 2011.

According to Rhomberg and his colleagues, the report's conclusions were not supported by the science, and were not consistent with NTP's own established criteria for listing a substance as reasonably anticipated to be a human carcinogen.

“Although a review of the data indicate otherwise, the report claims that humans have an increased risk of hematopoietic cancers, not lung cancers, as are seen in mice,” Goodman explains. “This shows not only a lack of concordance among laboratory animals—even within the same species—but also with humans.”

This analysis was also summarized and submitted as comments to the NTP during the review process for the RoC. The published summary can be accessed online at

[Note to editors: Gradient received financial support for the analysis from the Styrene Research and Information Center. The authors have sole, independent responsibility for its writing and content.]

About Gradient

Gradient is an environmental and risk science consulting firm renowned for specialties in toxicology, epidemiology, risk assessment, product safety, contaminant fate and transport, and environmental/ forensic chemistry.

Nancy Mayes, 703-772-2510

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