Styrene ranking upgraded to ‘probably carcinogenic’ to humans

Styrene, a key component for many plastics and synthetic rubber, is “probably carcinogenic to humans”, according to the International Agency for Research on Cancer (IARC).

An assessment this year by an IARC expert working group said there was now sufficient evidence to change its cancer rating from group 2B – possibly carcinogenic to humans – to 2A, a probable cause of cancer in humans.

Globally, manufacturers produce about 20m tonnes of styrene a year, according to the International Styrene Industry Forum (ISIF). This is used primarily as a monomer in the production of plastics, particularly polystyrene, which accounts for about half of global production.

The evidence from human studies – which focused on workers making reinforced plastics – was ‘limited’, said IARC’s monograph working group, in a summary paper published in The Lancet Oncology.

The studies did provide “credible evidence that exposure to styrene causes lymphohaematopoietic malignancies”, but there was no way to rule out “confounding, bias or chance.” Animal studies provided “sufficient” evidence of a cancer association.

Professor Henrik Kolstad of Aarhus University in Denmark, a member of the IARC working group, said: “The most recent styrene study shows the risk of acute myeloid leukaemia, a rare form of leukaemia, is doubled. Out of the more than 70,000 people included in the research project, we found 25 cases of acute myeloid leukaemia, where you would statistically expect to find 10.

“Research also found a five-fold increase in the risk of sinonasal adenocarcinoma – nasal cancer – among those who are exposed to styrene in the plastic industry.”

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