How to bury the evidence of work-related brain cancers

The chemical industry responded to unexpectedly high numbers of brain tumours at a US plant by launching a flawed study to obscure the extent of the problem, the Center for Public Integrity (CPI) has found.

The CPI investigation, the latest in its Science for sale series, examined a cancer cluster affected workers at the sprawling Union Carbide plant south of Houston, Texas. More than 7,500 people had worked at the plant, now owned by Dow, since it opened in 1941. It took three years, but by the late 1970s scientists at the federal safety regulator OSHA and its research arm NIOSH, discovered 23 brain tumour deaths there – double the normal rate. It was the largest cluster of work-related brain tumours ever reported, and in 1979 became national news.

The leading suspect was vinyl chloride, a chemical used to make polyvinyl chloride (PVC) plastic. Industry studies already had found higher-than-expected rates of brain cancer at vinyl chloride plants, and in 1979, the International Agency for Research on Cancer (IARC) took the unequivocal position that vinyl chloride caused brain tumours.

“Yet today, a generation later, the scientific literature largely exonerates vinyl chloride,” notes CPI. A 2000 industry review of brain cancer deaths at vinyl chloride plants found that the chemical’s link to brain cancer “remains unclear.” Citing that study and others, IARC in 2008 reversed its position.

However a CPI review of thousands of once-confidential documents showed that “the industry study cited by IARC was flawed, if not rigged.” Although that study was supposed to tally all brain cancer deaths of workers exposed to vinyl chloride, Union Carbide counted only one of the 23 brain tumour deaths in Texas City.

The Center’s investigation found that because of the way industry officials designed the study, it left out workers known to have been exposed to vinyl chloride, including some who had died of brain tumours. Excluding even a few deaths caused by a rare disease can dramatically change the results of a study, flipping a positive association on its head.

CPI warned that the decline in public funding for studies meant the “dominance of industry-funded research for specific chemicals has become more common.”

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