The risk assessment process has four general components

Technical Note DOER-R1

September 1998

several general components based on a USEPA framework (USEPA 1992) and recently published

USEPA guidelines (USEPA 1998). These components address the initial questions indicated

earlier. The risk assessment process has four general components:

Hazard Identification/Problem Formulation. Hazard Identification is the process of deter-

mining whether exposure to a contaminant can cause an increase in the incidence of a

particular human health (e.g., cancer, birth defect, etc.) or ecological (e.g., reproductive,

lethal, etc.) effect. In ecological risk assessment, the selection of receptors begins in this

section, but will continue into the Exposure Assessment.

Exposure Assessment. An Exposure Assessment estimates the magnitude of actual and/or

potential human or ecological exposure to a contaminant of concern, the frequency and

duration of exposure, and the pathways of exposure for human and ecological receptors. This

is the major step in the development of scenarios, and the decisions made during the Exposure

Assessment will be critical to the ultimate estimate of risk. To address concerns of stake-

holders it is important that this aspect of scenario development be a cooperative effort early

in the risk assessment process. An important component of Exposure Assessment is the

selection of human and ecological receptors. To a large extent, these will drive the develop-

ment of exposure pathways.

Toxicity Assessment/Effects Assessment. The Toxicity Assessment summarizes and weighs

available evidence regarding the potential for contaminants to cause adverse effects in

exposed individuals and provides, where possible, an estimate of the relationship between

the extent of exposure to a contaminant and the increased likelihood and/or severity of adverse

effects. Current guidance for Ecological Risk Assessment often refers to "Toxicity Assess-

ment" as an "Effects Assessment."

Risk Characterization. The Risk Characterization summarizes and integrates the Exposure

Assessment and Toxicity Assessment into a quantitative and qualitative expression of risk.

In a human health risk assessment, the Risk Characterization

Characterizes carcinogenic effects by estimating probabilities that an individual will

develop cancer over a lifetime of exposure based on projected intakes from a given

scenario and the information summarized in the Toxicity Assessment.

Characterizes noncarcinogenic effects by comparing calculated intakes of substances,

based on specific exposure scenarios, to acceptable doses.

Generally in an Ecological Risk Assessment, Risk Characterization evaluates risk by comparing a

concentration, dose, or body burden known to produce an effect, with a corresponding measurement

or projection of exposure made in the Exposure Assessment (toxicity quotient method). The risk

assessor may consider the toxicity quotient with other sources of information (biological conditions

at the site, information from reference areas) to form a professional opinion regarding potential risk

in a weight of evidence approach.

The Risk Characterization should also address uncertainty in the analysis of human health and

ecological risk. Risk assessments do not generally provide fully probabilistic estimations of risk.

Therefore, highly quantitative statistical uncertainty analyses are not common. The Office of

Emergency and Remedial Response (USEPA 1989) emphasizes the importance of identifying the

key site-related variables and assumptions that contribute most to the uncertainty.