The Science of Quantitative Risk Assessments


Finding their beginnings during the environmental awareness of the 1960’s and 1970’s, public health risk assessments were initially designed by industry as a reaction to public opposition. The purpose was not on public safety but instead was an exercise in arguing that the benefits of industrial pollution outweighed the risks (Starr 1969). The Secretary of Health, Education and Welfare (now called the Department of Health and Human Services) issued several briefs using this same reasoning concerning the use of pesticides and industrial chemicals (Griffith, Aldrich and Drane 1993:219). Yet the American public rejected that reasoning and placed pressure that, coupled with high profile environmental disasters, led to the passage of The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) in 1980.

With the internal challenges the passage of the CERCLA presented for the EPA, and the political climate of the industry-friendly Reagan administration, the risk assessment found itself with a new purpose – a defense against criticism of the EPA’s regulatory decisions.  Promoted by William Reilly, the EPA’s past director, the push for quantitative risk assessment actually arose with former EPA chiefs William Ruckelshaus and Lee Thomas (U.S. EPA, 1987). They positioned quantitative risk assessment as a basis for policy decisions when the federal courts and mounting citizen opposition challenged the accounting assumptions and the cost-benefit calculus of social impact that underlined EPA policy and air emission standards (U.S. EPA, 1987). The quantitative assessment of environmental health risk offered the EPA “a common denominator … by which the agency could rationalize and defend” itself within the often hostile special interests climate.  (Andrews 1994:217).

With the grassroots movement for environmental justice successfully blocking many new proposals for potentially hazardous sites, Ruckelshaus envisioned quantifying risk as a valuable “defense posture” against rising public sentiment against waste sites (Ruckelshaus 1983:51).  Proclaiming that we must "reject the emotionalism that surrounds the current discourse," he offered "objective science" in the form of quantitative risk assessment, and its subjective application through risk management, to improve public confidence in the EPA's decisions (Ruckelshaus, 1983:54). Reilly concurred, noting "science can lend a measure of coherence, predictability, authority, order, and integrity to the often costly and controversial decisions that must be made" (Reilly 1991:3).  Yet it can be argued that environmental science does not necessarily serve environmental justice because environmental science does not always consider the lived experience of environmental injustice (Brulle and Pellow 2006).

To illustrate that failing, we must examine the methodology behind the construction of a risk assessment.  A risk assessment is developed by utilizing a wide assortment of knowledge from fields such as toxicology, epidemiology, environmental health, biostatistics, pathology and industrial hygiene.  Risk assessments are typically completed in four stages (Moore 2007:510-512):

  1. Hazard Identification
  2. Dose-Response Analysis
  3. Exposure Assessment
  4. Risk Characterization

Each of these stages has issues inherent in its construction.  There exist biases or uncertain assumptions that form the epistemological grid on which a risk assessment is based.  A risk assessment is a collection of information given agency as an authoritative message.