Toxicity Assessment

contaminants of concern likely to occur at dredged material management sites.

These should be updated with each risk assessment as indicated in the following

steps.

The products of a toxicity assessment are:

a. A discussion of the potential adverse health effects due to exposure to

b. The toxicity factors for use in a quantitative estimate of risk.

Step 1: Determine Toxicity Factors

Carcinogenic effects of COC. EPA has used the weight-of-evidence approach to

evaluate potential human carcinogens and categorizes them in Integrated Risk

Information System (IRIS) (USEPA 1997) and the Health Effects Assessment

Summary Tables (HEAST) (USEPA/OSWER 1997). The carcinogenic slope factor

(CSF) expresses the carcinogenicity of a compound. The CSF is a toxicity value that

defines the quantitative relationship between dose and response. It is a plausible

upper-bound estimate of the probability of a response per unit intake of a

contaminant over a lifetime. The slope factor is usually the upper 95th-percent

confidence limit of the slope of the dose-response curve and is expressed as

(mg/kg/day) -1.

Noncarcinogenic Effects of COC. A reference dose, or RfD, is the toxicity value

used most often in evaluating noncarcinogenic effects, resulting from exposures to

chemicals. The RfD is defined as an estimate of a daily exposure level for the

human population, including sensitive subpopulations (such as elderly and children)

that is likely to be without an appreciable risk of adverse effects during a lifetime.

Step 2: Assemble Sources of Toxicity Information

There is a hierarchy of toxicity information that should be consulted when

conducting a risk assessment. The first is the Integrated Risk Information System

(IRIS), an information database that contains chemical-specific health risk and

USEPA regulatory information. Information in IRIS supersedes all other sources. If

information is unavailable in IRIS, then HEAST may be consulted. The HEAST

contains toxicity information and values from USEPA. It is updated quarterly and

contains interim toxicity factors that are not found on IRIS.

Human Health Risk Characterization

This text provides the toxicity factors which are quantitative estimates of the

potency of the contaminants of concern. These factors, combined with the average

daily intake estimates derived in the exposure assessment section, are used to

estimate risk in the risk characterization.

Chapter 4 Human Health Risk Assessment