Ecological and Human Health Risk Assessment Relationship

human and ecological receptors. To a large extent, these will drive the

development of exposure pathways.

c. 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 to

provide, 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 assessment" as an "effects assessment."

d. 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:

(1) 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.

(2) 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.

e. Uncertainty analysis. 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. USEPA/OERR (1989a) indicates the importance of identifying

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

uncertainty.

Ecological and Human Health Risk Assessment Relationship

At most sites, risk assessment will address two general types of risk, ecological

risk and human health risk. Ecological risk assessment focuses on potential risk to

nonhuman biota likely to occur at a disposal site. Human health risk assessment

focuses on carcinogenic and noncarcinogenic risk to humans from potential

exposure. A major difference between the two is that a human health risk

assessment addresses potential effects to one type of receptor, human beings, while

Chapter 1 Overview of Ecological and Human Health Risk