Policy by analogy: precautionary principle, science and polybrominated diphenyl ethers

Through the acquisition of scientific data, knowledge is gained about the environmental fate and human exposure of chemical substances. From this knowledge, the risk of using chemicals can be assessed. As a means of facilitating the regulatory process, risk assessments can also compare the substance under investigation to other substances that display similar behaviour or structure, especially when the risk assessment involves a substance for which few data exist. For instance, similarities can be drawn between a number of poorly studied chemical substances and those that are currently listed as chemicals of concern. We suggest that policy can be guided, in part, by analogy. By taking advantage of knowledge obtained for the PCBs in the past, we can better implement precautionary measures with respect to similar substances, such as the PBDEs, and do so more quickly and appropriately.