Health Risk Assessment for Radiological, Chemical, and Biological Attacks*

To evaluate potential health effects from a radiological, chemical, or biological agent following intentional contamination—whether to water, air, or environmental surfaces—some type of health risk assessment is necessary. Risk assessment parameters are defined in the context of “risk informed” decision-making. A risk-based approach means that cleanup goals should be based on a defined, “acceptable,” or “tolerable” level of risk to health. For weapons of mass destruction, regulations and guidelines for what constitutes an acceptable human dose are clearest for radiological agents, less clear for chemical agents, and least codified by far for biological agents. The Environmental Protection Agency (EPA) has developed an updated Protective Action Guides to help authorities make radiation-protection decisions during the phases of an emergency. No uniform set of cleanup standards for radionuclides exists at present, but the Department of Homeland Security has posted proposed guidelines in the Federal Register to address response operations. The consensus for item clearance criteria (a voluntary standard) is currently 1 mrem/year (or 10 μSv/year) total effective dose equivalent above background. EPA standards for concentrations of various radioactive isotopes in groundwater and drinking water are reviewed along with primary drinking water standards. For chemical warfare agents and toxic industrial chemicals, several authorities have published quantified, health-based guidelines that can be used as “accpetably safe” clearance goals, and these values are reviewed. For example, both the EPA and the military use maximum contaminant levels as enforceable guidelines for chemical agents in drinking water. Although nearly all biological warfare agents are intended for aerosol application, many have a strong potential as waterborne threats and could inflict heavy casualities if ingested. Scientific investigations have led to recommended guidelines in drinking water for only some of the biological warfare agents that have been identified as priority microbes or microbes of medical importance in water. Most researchers agree that there is currently insufficient information to develop; an infectious dose and to quantify a “safe” amount of residual biological agent in a decontaminated facility or outdoor environment. There is even less information regarding safe levels for water resources. Education should not be underestimated when considering what risk the public is willing to accept. Individual states have drinking water relations based on their stakeholders, and such information must be considered when trying to determine guidelines applicable to an unnatural even. Major gaps, critical needs, and future directions associated with evaluating risks to human health following a terrorist attack are summarized. Keywords: biological warfare agent; chemical warfare agent; clearance goal; radiological agent; risk assessment