Message in a bottle: claims disputes and the reconciliation of precaution and weight-of-evidence in the regulation of risks from Bisphenol A in Canada

In this article, we examine scientific and political controversies surrounding the assessment and management of environmental health risks from the substance Bisphenol A. The Government of Canada recently declared the substance toxic and implemented a ban of baby bottles containing Bisphenol A to reduce infant exposures despite objections from industry, some scientists and policy makers in other jurisdictions that the current weight-of-evidence does not justify these measures. Bisphenol A was reviewed under Canada's Chemicals Management Plan whereby the government is legally obligated to use a scientific weight-of-evidence and precautionary approach. However, tensions remain over how to distinguish and reconcile the two. We analysed peer review literatures, policy and legal documents, and key informant interview transcripts to determine evidence selection, contested claims and related efforts undertaken to have particular interpretations of weight-of-evidence and precaution legitimised. We discuss various factors within the Canadian context that influenced the trajectory of claims-making disputes, including how ‘weight-of-evidence’ and ‘precaution’ were employed. We advance understandings of why Canada became the first national government to declare Bisphenol A toxic, an internationally contentious, albeit increasingly precedent setting, policy response. We also identify the need for a better understanding of the science base of precautionary ideals and how uncertainty is normatively and factually negotiated with respect to harm, exposure and hazard matters. We argue improving regulatory deliberation requires enhancing the transparency and democratic scrutiny of expert-driven assessments given that the boundaries between that which is normative versus objective, technical versus political, scientific versus precautionary, are not always distinct or agreed upon.