Women who have worked for companies that make plastic injection molded parts for the auto industry have a significantly higher risk of developing breast cancer than women who have not been exposed to that type of working environment, says a team of 12 researchers whose work was funded by a number of Canadian groups, including Health Canada.
The report, published Nov. 19 in the Journal of Environmental Health, examined the occupational backgrounds of 1,006 women with breast cancer in the Ontario counties of Essex and Kent and compared them with a control group of 1,146 women in the region who did not have breast cancer.
The breast cancer study group of 1,006 women included 26 women who worked in the plastics automotive sector. Based on that group of 26 women, the report said women in the plastics automotive sector were almost five times more likely than women in the control group to develop breast cancer prior to menopause.
“One year in plastics [auto] employment is estimated to increase the odds of breast cancer by 9 percent,” said the report, with the cases of “excess breast cancer” largely “limited to small automotive parts suppliers, which would include some plastics operations.”
The report does not contain information directly linking the exposure of those 26 women to any particular chemical or identify any specific chemicals to which those women had been exposed on their jobs. It simply notes that the women in those environments are exposed to a wide number of chemicals that have been suspected of causing cancer.
The American Chemistry Council, based in Washington, took exception to that analysis.
“It is concerning [to us] that the authors could be over-interpreting their results and unnecessarily alarming workers,” ACC said in a statement issued Nov. 19, after it had the opportunity to review the full study. “This study included no data showing if there was actual chemical exposure, from what chemicals, at what levels, and over what period of time [exposure might have occurred] in any particular workplace.
“Although this is a worthy and important area of research,” ACC said, “it is inappropriate to use such research as the basis for speculation about causes of patterns of cancer rates among occupations without any information of substance about whether there are actual exposures, to what actual substances, and how big [those exposures] might be.”
John Heinze, a scientist who works for a non-profit research group in Washington, concurred.
“This is ... basically a survey of the jobs held by over 1,000 Canadian women who had breast cancer compared to an equal number of women who didn't have breast cancer,” Heinze said in an interview.
“Since the case and controls were supposedly matched on other health and demographic variables, any difference in breast cancer incidence was assumed [by the researchers] to be due to occupational exposure to carcinogens and endocrine disrupters,” he said.
“However, occupational exposures were not measured, nor were questions asked specifically regarding occupational exposures,” said Heinze. “So the results ... only demonstrate statistical associations, not cause and effect. Without measurement of exposure levels, the statistical comparison of job histories between the two groups is not meaningful [and] the paper offers very little but speculation.”
The 12-person research team does not cite specific evidence or link the higher cancer rate among the automotive workers to any specific chemical exposure.
Instead, the report simply noted that a number of plastics used in plastic manufacturing have been “identified” as endocrine-disrupting chemicals and that there are a number of ways workers making plastic injection molded parts can be exposed to “harmful” chemicals.
“Many plastics have been found to release estrogenic chemicals, [and] such additives as phthalates and polybrominated diphenyl ethers have been identified as endocrine-disrupting chemicals,” said the report.
“Additionally, some of the monomers present in the manufacturing of polymers have been identified as mutagenic and/or carcinogenic [and] several monomers, additives and related solvents, such as vinyl chloride, styrene, and acrylonitrile have been identified as mammary carcinogens in animal studies,” said the report. “Cumulative exposure to mixtures of various estrogenic chemicals may compound the effect.”
Similarly, the report did not delineate any specific ways the women in the study had been exposed to such chemicals. It simply pointed out how such workers could potentially be exposed to those chemicals.
“Emissions of vapors or mists from these hot [injection molding] processes can include plasticizers, ultraviolet-protectors, pigments, dyes, flame retardants, unreacted resin components and decomposition products,” said the report. “Further exposure [to potentially harmful chemicals] can come from skin contact in handling and performing finishing tasks.”
Again, ACC disagreed and noted that there was no determination made by the researchers of any specific exposures.
“The study only demonstrates statistical associations. And, the study only examines occupations, not exposures to any agents or substances,” ACC said.
“Since there is no actual determination of exposures to such substances [and] no documentation of the presence in the workplace” of those substances, “there is no basis to conclude that exposures to such substances are any different for cases rather than controls,” ACC said.
The chemical industry group also said the American Cancer Society does not list chemical exposures among the well-established risk factors for breast cancer.
ACS instead lists a combination of lifestyle and genetic factors that include gender, aging, genetic risk factors, family or personal history of breast cancer, race and ethnicity, dense breast tissue, early menstruation, late menopause, previous chest radiation, diethylstilbestrol exposure, not having children or having a first child after age 30, some forms of birth control, hormone therapy after menopause, alcohol, being overweight or obese and lack of physical activity.
ACC also pointed out that the National Cancer Institute has said that “research does not show a clear link between breast cancer risk and exposure to chemicals in the environment.”
The breast cancer study of the Canadian women was supported by the Department of Sociology, Anthropology and Criminology of the University of Windsor and the National Network on Environments and Women's Health, which received funding from Health Canada through the Women's Health Contribution Program.
Additional research partners included the Windsor Regional Cancer Centre of Windsor of Windsor Regional Hospital, and the Occupational Health Clinics for Ontario Workers, with additional funding provided by the Ontario region of the Canadian Breast Cancer Foundation, the Breast Cancer Society of Canada, the Windsor Essex County Cancer Centre Foundation and the Green Shield Foundation.