Environmental Engineering Reference
In-Depth Information
standard is lacking, soil quality assessments can be based on provisional soil quality
standards, that is: soil quality standards that are not formally accepted, but that
reflect the best available knowledge on the contaminant. Using provisional quality
standards, one could also calculate a provisional Hazard Index. If sufficient ecotox-
icity data are available, however, one can use those data also to determine the SSD,
and subsequently quantify the toxic pressure associated to the concentration of the
contaminant.
For certain contaminants, namely those which often occur together, it is techni-
cally possible to derive group soil quality standards, when the composition of such
mixtures of contaminants is known and more or less constant. This has been done,
for example, by Traas (
2003
) for Dutch standards for the sum of ten different PAHs
in soil. Such standards simplify the assessment and regulation of mixtures.
After a contaminant is allowed to be produced and used based on an evaluation
of expected exposures and sensitivity data, an Outcome Assessment could be based
on an analysis of soil quality monitoring data. When the Risk Assessment mod-
els appropriately predict real-world phenomena, no exceedances of the soil quality
standards should be found when the product is used. If exceedances are nonethe-
less found, appropriate management actions can be derived and taken, and a further
Outcome Assessment would show whether those actions were effective.
14.13.3 The Dilemma of Conservative Quality Standards
Criterion Risk Assessments are used to set and implement soil quality standards. In
setting such standards, authorities should be well aware of a potential dilemma that
may arise when protective soil quality standards are applied: they may trigger far
more regulatory actions than anticipated or they may elicit large public concerns.
Posthuma et al. (
2008
) have described this dilemma. On the one hand, it was
explained that the use of soil quality standards in environmental management has
been highly successful. Many contaminants have been banned or their emissions
have been reduced, thereby reducing toxic pressure on soil communities. The
success of this approach is most easily seen in aquatic systems where the ecolog-
ical status has improved considerably over the last decades, in large part due to
standards-based bans and regulations.
But on the other hand, the lower the protective soil quality standards or remedia-
tion trigger, the larger the areas of soils considered “contaminated”, and the higher
the number of “candidate remediation cases” in an area, respectively. The general
public might consider cases that are not clean as being “dangerous”, and this would
in turn require substantial communication on the risks of slight soil contamination.
In short, the more conservative the bias in standard setting, the bigger the public
concerns and the Risk Management problem may be.
So, due to this dilemma, low soil quality standards are good for soil protection,
but bad for optimizing environmental management and for the public perception of
existing risks. As a general solution,
tiered approaches in soil appraisal
should be
designed and implemented, to improve assessment accuracy and to better inform
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