Risk Assessment is a scientific process that predicts the risk faced by humans, plants, or animals if they are exposed to a contaminant. Human Health Risk Assessments (HHRA) focus on possible health risks to people, while Ecological Risk Assessments (ERA) examine the potential impacts to ecological receptors. In the Sudbury Soils Study the ERA focused on terrestrial plants and wildlife.

In both types of assessment, researchers look at the effects that may arise over long-term exposure to the Chemicals of Concern (COC).

Several key steps are followed in a risk assessment study:

1) Problem Formulation
Understanding the past, present and future uses of the site.

2) Identification of the Hazard
Review any scientific literature to identify the nature of known or suspected effects from the substance(s) under study.

3) Determine the Level at which Harm Might Occur
Review various guidelines that have been published to predict at what level harmful effects might occur.

4) Identify the Level of Human or Environmental Exposure
Collect air, water and soil samples to estimate how much exposure people or the environment have had to the substance(s) under study.

5) Identify Community Risk
Compare estimated exposures (4) with acceptable exposure limits for the substance(s) under study, to determine the likelihood of health effects on humans and the environment.