Environmental Engineering Reference
In-Depth Information
the public when generic standards are exceeded (Posthuma et al.
2008
). The simple
alternative, a general “relaxation of the soil quality standards to avoid the dilemma”
is not an option, due to the success of soil quality standards in preventive soil
policies.
14.13.4 From Criterion Risk Assessment to Conventional
Risk Assessment
Due to the application of soil quality standards in practice, a three-part discrimina-
tion of soil contamination problems has resulted in many countries:
•
“clean” (or non-polluted) soil, in which the low-range soil quality standard which
was designed in the context of soil protection is not exceeded; this signals no
unacceptable risks, and generally no public concerns;
•
“contaminated” soils, in which the protective criterion is exceeded for one or
more compounds;
•
“highly contaminated” soils, in which the soil standards trigger serious concerns
with respect to local risks.
The further content of this chapter concerns the latter two classes. In these situa-
tions, SSDs are used to quantify local toxic pressures, and to use the outcomes from
such assessments for Risk Management.
14.13.5 Conventional Risk Assessments with SSDs:
A Versatile Approach
Conventional Risk Assessments are done when there is a current or an expected
source of a contaminant (or a contaminated site), and an estimate of the type and
magnitude of effects (with or without confidence intervals) is required.
For Conventional Risk Assessments we need to combine SSD-modeling together
with exposure modeling, including bioavailability assessment (see
Chapter 16
by
Hodson et al., this topic) and mixture modeling (Section
14.10.6
), to take into
account local conditions. Combining these methods results in
a single estimate of
the net toxic pressure of site contamination
(or predicted impacts of future con-
tamination levels, given e.g. current emissions), quantified as msPAF. Such net risk
output has three uses:
1.
the msPAF-value can be compared to a policy-adopted maximum-acceptable
fraction of species
or
fraction of functions
that might be affected to determine
whether the mixture elicits toxic pressures lower or higher than that effect-related
limit;
2.
it can be used to rank sites within a list of suspected risky sites on the basis of
overall toxic pressures; in this case, software can be developed to handle large
sets of soil concentration data (examples are provided below); or
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