Environmental Engineering Reference
In-Depth Information
contaminated site is not always known, the definition of the relevant exposure time
also is a political issue. It could politically be stated, for example, that in principle
it should be possible for humans to work at a contaminated site for a period of 40
years (working lifetime), without experiencing unacceptable adverse effects due to
soil contamination.
The political role is even more pronounced for the derivation of Soil Quality
Standards. As was described in Section 5.5.2 , one or more generic exposure sce-
nario(s) have to be defined as an important basis for the derivation of Soil Quality
Standards. In fact, the exposure time, or the duration that humans perform different
tasks at a contaminated site, must be part of this exposure scenario. According to
the Dutch Soil Protection Act, for example, a political boundary condition for the
derivation of Soil Quality Standards ( Intervention Values , used in the first tier Risk
Assessment) is that humans must be able to reside their whole lifetime on a con-
taminated site. Although this is hardly a realistic condition, certainly in case of any
land use other than Residential, it is believed to represent an acceptable worst-case
(conservative) criterion to be used in the first tier Risk Assessment. An exception
is made for lead for which only the child phase is considered, since human health
effects are much more relevant during the child phase.
Time span should not just be considered in the Exposure Assessment; it
is also a key component in Risk Characterisation, as Estimated Exposure and
Critical Exposure values should be consistent with regard to duration. Exposure
Assessments at contaminated sites generally address long-term exposures, thus aver-
aging out any peak exposures occurring at the site. This is generally appropriate for
residential or industrial sites, as peaks in exposure are not expected. One exception
is pica behaviour, particularly by small children, where deliberate ingestion of large
amounts of soil particles could result in peak exposures that go well beyond typical
assumptions (e.g., Lemanek et al. ( 2002 ), who examined the incidence and relation-
ship of pica symptoms and dysfunctional eating patterns in children and adolescents
with sickle cell disease).
Scenarios with intermittent exposure, for example, in contaminated recreational
areas where exposures take place only for a few hours per day, for a few days a
year, would, however, require consideration of the potential health effect of this
short-term exposure.
A third aspect in regard to time span is the toxicologically relevant exposure
period in the lifetime of the exposed population. Lead, for example, is well-known
to cause neurological effects by children, but can affect the kidneys at higher and
longer exposure levels. Moreover, health effects can be related to the average daily
dose, but can also be related to the cumulative dose.
Susceptibility can change with age, and much attention is paid to the susceptibil-
ity of children or the elderly for exposure to contaminants (International Programme
on Chemical Safety 2006 ; US Environmental Protection Agency 2006 ). A number
of pieces of legislation account for the protection of children by performing the Risk
Characterisation of threshold contaminants upon exposure during the first years of
age (0-6 years). This practice is applied, for example, in the United Kingdom and in
Flanders (Belgium). As children will have a higher exposure per unit of body weight
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