Environmental Engineering Reference
In-Depth Information
Conventional Risk Assessments begin with a current or expected source of a
contaminant or a contaminated site, which is used to estimate exposure, either for a
single contaminant or a mixture. The exposure estimate is then used in an exposure-
response model to estimate the probable magnitude of effects (like the “forward”
use of distribution models in Panel B or C in Fig. 14.3 ). When using SSDs in this
way, assessors must pay particular attention to ensuring that the exposure models
or measurements reflect conditions in the field and are equivalent to the exposure
metrics in the exposure-response models.
The outcomes of Criterion Risk Assessments and Conventional Risk
Assessments can result in follow-up assessments (Suter and Cormier 2008 ):
3. Management Assessments . These assessments predict the results of one or more
management alternatives that can be undertaken to reduce risks, like emission
reduction, or the application of various remediation techniques. They consider
risks, costs, benefits and legal requirements.
4. Outcome Assessments. These assessments can be used to determine whether the
management action was effective (e.g., when concentrations have been reduced
to the desired levels) and whether environmental goals have been achieved (e.g.,
when biotic communities have recovered).
In Sections 14.13 and 14.14 , each of these assessment types is illustrated, with
SSDs as a key part of the evaluation approach. It is shown that SSD-based results,
with appropriate Exposure Assessment modeling, are specifically relevant for rank-
ing ecological hazards, and that they can therefore be used to explore the results of
alternative soil management scenarios. The theory and practical examples presented
in this chapter show that SSDs may help to improve effectiveness in the management
or remediation of contaminated soils .
14.4 Theoretical Basis of SSD Modeling
Though Fig. 14.3 is the illustrative basis for distribution-based modeling, there is
more to say on the theoretical basis of distribution-based modeling in Ecological
Risk Assessment. Hence, this section describes a range of technical aspects of
SSDs, from basic principles to derivation and interpretation of SSDs and on refined
issues like presenting confidence intervals and accounting for natural background
concentrations of contaminants. We mainly focus on concepts, understanding and
illustrations rather than on mathematical formulae; the latter can be found elsewhere
(e.g., Posthuma et al. 2002b ).
14.4.1 Why SSDs Fit the Risk Assessment Paradigm and Practices
SSDs are well suited to the general concept of Risk Assessment. Risk concerns
both the probability of an adverse effect and the magnitude of such an effect. How
distributional statistics relate to Ecological Risk Assessment is shown in Fig. 14.4 .
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