Risk assessment of butadiene for the Existing Substances Regulation (ESR) in the European Union

The European Commission's Existing Substances Regulation (ESR) requires an evaluation of the risks to humans (workers, consumers and the general public) and the environment, posed by selected existing chemical substances. The Regulation focuses initially on high tonnage chemicals, and in this first year of the ESR, the UK undertook to produce the risk assessment document for 1,3-butadiene. This was in recognition of a need to reconsider the regulatory position in the light of new and ongoing research. In particular, the risk assessment was an opportunity to address the current debate over the animal toxicity data, where marked species differences exist, and the relevance of these data for human health. The human health part of the risk assessment of butadiene involves a comparison of health effects against exposures in the three population sectors. In this paper, the approach to risk assessment is exemplified for the occupational exposure setting. The conclusion reached for the human health hazard assessment has been influenced significantly by both the available animal and human data. Species differences in toxicity, in particular with regard to mutagenicity and carcinogenicity, have been considered, along with the mechanistic arguments for these differences and their relevance for human health. In addition, the evidence for health effects in humans is considered. The overall conclusion of the health hazard assessment is that there is concern for genotoxicity and for carcinogenicity, for which a threshold of effect cannot be identified. The occupational exposure assessment indicates that exposure in the workplace is generally well-controlled, of the order of 3-5 ppm or below. The overall conclusion of the risk assessment for the occupational setting is that there is concern for the possibility of genotoxicity and carcinogenicity at the exposure levels which occur in some European workplaces.