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 method and the application of a weight of evidence approach recently developed in
the state of Massachusetts.
Risk characterization is an integration of the exposure assessment and effects
assessment to judge whether the predicted exposure to the COC are of sufficient
magnitude to produce the effects associated with the selected toxicity factor.
The assessment should characterize risks with respect to the stated assessment
end points. This requires integrating exposure and effects information specific to
that assessment end point.
For each assessment end point, the risk characterization should:
a. Estimate the area(s) within which receptors or habitats are considered to be
at risk.
c. Provide information on the persistence or duration of these estimated risks.
d. Identify the pathways and other conditions which contribute to the risk.
e. Identify and characterize the uncertainties associated with the risk
estimates.
The risk characterization integrates effects and exposure information in one or
more of several methods, including quotient methods, weight-of-evidence or lines-
of-evidence approaches, and probabilistic methods.
Generally, risk characterization uses a direct numerical comparison between the
exposure concentration, dose, body burden, or dietary concentration and their
associated toxicity factors. If the ration between them is greater than one, there is
potential for risk. In those instances where an assessment end point has several
measurement end points (and hence several toxicity factors to compare with each
measurement end point), risk characterization may use a weight-of-evidence
approach.
Quotient Method
The Quotient Method is a simple tool for comparing exposure concentrations to
toxicologically effective concentrations:
HQ = EPC/TF
(5)
68
Chapter 3 Ecological Exposure Assessment
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