Dioxin and

Quantitative Risk Assessment



James Klinck



Dioxin, an unwanted contaminant of organochlorine compounds, is one of the most toxic chemicals ever studied. Dioxin, due to its persistence in the environment, is ubiquitous; people throughout the world are carrying substantial body burdens of dioxin. The U.S. Environmental Protection Agency began a reassessment of the toxicity of dioxin in 1991. The dioxin reassessment released in 1994 demonstrates that dioxin produces a broad array of adverse health effects including reproductive and developmental disorders, immune system suppression, and endocrine system disruption.


In 1980 Congress passes the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). The Act created Superfund to clean up the most dangerous toxic sites in the U.S. The EPA has been charged with implementing CERCLA. The U.S. EPA has relied upon the procedure known as quantitative risk assessment (QRA) to identify and quantify the risks associated with the various compounds found in toxic sites. Endorsed by William Ruckleshaus during his second tenure as director of EPA, QRA has often been used as a tool to limit public participation in the decisions concerning potentially toxic compounds. Quantitative risk assessment is based on determining an acceptable level of risk; the acceptable levels of risk are often derived based on assumptions and regularly with sufficient data. Depending on the assumptions used, the conclusions reached through QRA can vary significantly.


The dioxin reassessment prepared by the EPA has recognized the inherent limitations of QRA, and appears to disaffirm the justification of the site specific use of risk assessment. Instead the reassessment appears to support the use of risk assessment as proposed by the Interagency Regulatory Liaison Group: The IRLG supports the use of risk assessment only to establish priorities and to obtain rough estimates of risk.


A legal infrastructure known as the Precautionary Principle has been gaining acceptance throughout the industrialized world, with the exception of the U.S. government. The Precautionary Principle, while not based on a universally established definition, espouses the concept that powerholders must not wait until damage has been proved before acting to protect the environment. The International Join Commission on the Great Lakes, for example, has proposed a phaseout of an entire class of persistent compounds known as organochlorines. The EPA dioxin reassessment demonstrates that dioxin-like compounds must be phased out as a class of chemicals.