Environmental regulation in the United States has been characterized by short-term decisions with unknown or unanticipated long-term public health consequences. Some propose to use our inability to predict possible long-term consequences of environmental health regulation as a justification for replacing risk assessment with the "precautionary principle" as the dominant paradigm for making regulatory decisions. The precautionary principle is based on the idea that it is better to be safe than sorry; that is, precaution reflects the need to take action in the face of potentially serious risks without awaiting the results of scientific research that establishes cause-and-effect relationships with full scientific certainty.¹ In contrast, U.S. law reflects a traditional suspicion of government regulation, requiring extensive factual records proving "significant risks" to justify regulation aimed at protecting public health from environmental contaminants. This fundamental norm of the U.S. legal culture, sometimes called the "principal of legality," makes precautionary environmental health regulation difficult because government must assemble a factual record to support its actions.

Support for the precautionary principle is motivated in part by a desire for a more agile legal system that does not use incomplete science as a reason to postpone regulating. But the long-term consequences of substituting precaution for risk-based decisions could undermine the already somewhat meager scientific basis for regulatory actions unless we develop improved mechanisms to revisit decisions as better scientific information develops. Meanwhile, huge investments continue to be made in complying with regulation of chemical contaminants despite our limited ability to demonstrate the impact of that investment on improving public health. In that sense, environmental health regulation in the United States already implements the precautionary principle on a grand scale. This Dialogue argues that applying a combination of both risk assessment and the precautionary principle in environmental regulation, along with an improved environmental health infrastructure, are needed to protect public health and the environment more effectively.