The study, Cancer Mortality of Workers Exposed to Styrene in the US Reinforced Plastics and Composite Industry, has been published in the journal Epidemiology

Study reference
Cancer Mortality of Workers Exposed to Styrene in the US Reinforced Plastics and Composite Industry, Collins, JJ; Bodner, KM; Bus, JS; Epidemiology, March 2013, 24(2), 195-203.

“These findings, which are based on 60 years worth of epidemiology data on cancer risks associated with workers exposed to relatively high levels of styrene, completely undercut the US National Toxicology Program’s listing of styrene as ‘reasonably anticipated to be a human carcinogen’ in its 12th Report on Carcinogens,” says Jack Snyder, executive director of the Washington, DC-based SIRC, which supported the study. 

In its February statement, the SIRC reports that the authors examined mortality rates associated with cumulative exposure, duration of exposure, peak exposures, average exposure and time since the first exposure of styrene, and concluded: “[W]e found no increased mortality from lymphatic and hematopoietic tissue cancers overall or in any sub-diagnoses including non-Hodgkin lymphoma, Hodgkin lymphoma, multiple myeloma or leukemia in this highly exposed group of styrene workers. Further, no exposure response was associated with cumulative daily peak exposure or number of peak exposures …

“Lung cancer rates, while greater than expected, appeared to be unrelated to styrene exposure and more likely attributable to smoking. In this large study with relatively high styrene exposure, we find no credible evidence that styrene exposure increases risk from cancers of the lymphatic and hematopoietic tissue, pancreas, or lung.”

This new report adds 19 years of follow-up mortality data to a study of workers in the reinforced plastics industry published originally in 19903 and updated in 19944. Studies involving workers in the reinforced plastics industry are considered the most informative because styrene exposure typically is higher than in other industries where styrene is used, confounding from other potentially carcinogenic exposures is uncommon, and the study populations are large.

“This updated analysis substantially adds to the evidence that indicates a lack of association between styrene exposure and cancer,” says Julie Goodman Ph.D., DABT, a toxicologist with Gradient.

Goodman co-authored a recent weight-of-evidence analysis of styrene research, concluding that studies in humans, and particularly workers with high styrene exposures, show no consistent increase in death from any type of cancer.

National Academy of Sciences review

In June 2011, the US Department of Health and Human Services listed styrene as a substance that is “reasonably anticipated to be a human carcinogen” in its 12th Report on Carcinogens (RoC). The American Composites Manufacturers Association (ACMA) and SIRC opposed the listing. (See:ACMA opposes listing of styrene as 'reasonably anticipated’ carcinogen.)

On 19 February, the ACMA sent a letter to a National Academy of Sciences (NAS) peer review panel in which ACMA Chief Staff Executive Tom Dobbins encouraged the panel to "clarify the current confusing situation" regarding the carcinogenic potential of styrene. The NAS peer review was ordered by Congress to address composites industry concerns with the scientific validity of the listing of styrene as a "reasonably anticipated" carcinogen in the National Toxicology Program (NTP)'s Report on Carcinogens.

Styrene and composites

Styrene monomer is a component of unsaturated polyester resin (the most widely used resin in the fibre reinforced plastics industry). It provides crosslinking sites and reduces the polyester to a workable viscosity. Composites industry groups point to evidence that workers can safely work with styrene when using protective equipment and by limiting possible exposure to emissions. However, in view of the heath and safety concerns surrounding styrene, some companies have been researching styrene-free resins. The questions are: can styrene-free resins provide the same performance as styrene-based resins?; can they be processed the same?; and will their cost be acceptable? 

Further information:

Dobbins told the NAS panel that the public may be confused about styrene and cancer because NTP’s styrene listing is "at odds with recent authoritative reviews, each of which found no support for a cancer concern for this substance." Authorities such as the Danish EPA and the Texas Commission on Environmental Quality recently reviewed the same data as NTP but determined that styrene is not likely to cause cancer, the ACMA says.

"These different conclusions based on the same scientific information cause confusion regarding the health risks potentially associated with our industry’s operations," the ACMA letter states.

"We are also concerned about the RoC listing," Dobbins continues, "because, during its review of the styrene data, a number of decisions by NTP seemed poorly supported, opaque, or ad hoc, and may have lessened the scientific validity of its styrene conclusion."

The letter states that NTP, for example, appears to have disregarded high quality industry-worker studies finding no cancer effect, in favour of lower quality studies that provided data justifying the RoC listing.

The NAS styrene panel will hold its first public meeting on 19 March and is expected to issue its peer review report in 2014.