By Jessica John Bowman
The 12th Report on Carcinogens, released by the U.S. Department of Health and Human Services on June 10, 2011, lists Styrene as
a chemical “reasonably anticipated to be a human carcinogen.” The National Toxicology Program, which drafts the report, based its
listing on experimental animal studies, limited evidence of carcinogenicity from human studies, and other evidence. The evidence of
carcinogenic effect in humans is based largely on occupational studies in two major industries: the reinforced-plastics industry and
the styrene-butadiene rubber industry. In both industries, styrene-exposed workers were found to face an increased risk of leukemia,
lymphoma, or all lymphohematopoietic cancers. Although the report recognizes that the evidence associated with workers in the
styrene-butadiene rubber industry is limited, due to the associated exposure of such workers to other known
carcinogens including butadiene, the report indicates that the finding of increased risk of cancer in the
reinforced-plastics industry is much stronger, due to the absence of cross-exposure to other known
carcinogens in that industry. Although the report stops short of finding causality, due to
the risks associated with confounding from exposure to other chemicals, it nonetheless
concludes that “a causal relationship between styrene exposures and cancers in humans is
credible.”
In addition to the industrial groups mentioned above, styrene is used in the production
of a number of other goods, including insulation, carpets, paints, polishes, adhesives,
packaging, insulation, refrigeration equipment, tanks, pipes, and, increasingly,
housewares such as food containers and toys. While workers who manufacture these
goods may face a lower exposure rate than workers in other areas, manufacturers
should take note of the report’s findings and its potential implications for both their
workers and their customers. A copy of the report may be found here.
The impact of the report’s classification of styrene will likely be substantial, and
styrene industry groups are expected to take legal action to block or revoke the listing.