Risk assessment, remedial decisions and the challenge to protect public health: the perchlorate case study

While scientists have a responsibility to defer judgment in the absence of conclusive data, public health and ecological protection require that government regulators make decisions based on available information. The risk assessment paradigm has evolved to help risk managers balance risks to public health with the cost of pollution control and remediation. Risk assessments are designed to be reasonably protective of public health, however the time and money required to develop and evaluate a robust scientific database can significantly delay regulatory action while exposures continue. The federal assessment of perchlorate, a component of rocket fuel and a thyroid toxicant, is presented here as a case study that demonstrates some of the limitations of risk assessment in protecting public health. Perchlorate was detected in a city well field that lies beneath a military training range at Aberdeen Proving Ground, a U.S. Army garrison in Maryland. Cleanup was put on hold, pending promulgation of a national drinking water standard for perchlorate. This case study (1) illustrates the challenge of preventing chemical exposures in the absence of promulgated standards, and (2) makes recommendations for approaches to preventing exposures to chemicals of unknown, or uncertain toxicity before they occur.