In the December 2005 issue of this journal, Sathiakumar and colleagues¹ report on the extended follow up of the University of Alabama cohort in the styrene–butadiene–rubber industry. The update confirms the increased risk of haemato-lymphopoietic malignancies in work areas with high exposure to butadiene and styrene. This study is both potentially informative and at the centre of controversies regarding the evidence for the human carcinogenicity of butadiene and styrene.

In 1999, an IARC Working Group concluded that butadiene is “probably carcinogenic to humans” (Group 2A) on the basis of “limited evidence” of carcinogenicity in humans and “sufficient evidence” in experimental animals.² A case-control study nested in the University of Alabama cohort³ showed a consistent excess of leukaemia and a statistically significant dose–response relationship with cumulative exposure to 1,3-butadiene, which remained after adjustment for exposure to styrene. Studies among workers in butadiene production reported an excess of lymphohaematopoietic cancers.

In 2002 a separate IARC Working Group concluded that styrene is “possibly carcinogenic to humans” (Group 2B) on the basis …