Human Health Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 245

and that from the contaminated site. From this perspective, reduction of exposure
from the contaminated site or from background sources is of equal importance.
Intervention measures should ideally focus on the most effective way of reducing
exposure. Often reducing voluntary background exposure is the most promising and
effective.
Whether or not to include background exposure in Risk Assessment and Risk
Management is, however, a political issue. From a political perspective, different
viewpoints on the role of (imposed) background exposure in Human Health Risk
Assessment are possible. One viewpoint follows the medical approach, the most
pure approach from a toxicological perspective. This implies that exposure from
the contaminated site must be added on to the (imposed) background exposure and
the combined exposure may not exceed the specific Critical Exposure. Or, in other
words, exposure due to contaminated sites may not exceed a Critical Exposure (aka:
Toxicological Reference Value), reduced by the (imposed) background exposure
(see Fig. 5.6 ).
One practical problem is that for some contaminants the (imposed) background
exposure fills up a substantial part of the Critical Exposure values and sometimes
even exceeds the Critical Exposure values. In that case, the human health risks due to
contaminated sites cannot be assessed on the basis of 'the medical approach'. This
aspect could result in conflicts when setting Soil Quality Standards. In Flanders,
for example, background exposure is taken into consideration (Provoost 2004a , b )
and could therefore constitute a substantial part of total exposure. In the UK
(Environment Agency 2008 ) and in Germany (Bachmann et al. 1999 ), background
exposure is limited to a specified proportion of the Critical Exposure value for every
contaminant.
Another principle refers to the fact that the policy on contaminated sites can only
control exposure due to contaminated sites, and must take the (imposed) background
exposure for granted. According to this philosophy, it is politically defensible to
only assess the exposure due to contaminated sites. In other words, independent of
background exposure and, hence, of the overall effects, the exposure due to con-
taminated sites may not exceed Critical Exposure. Since humans may not be 'fully
protected' according to this philosophy, and it would thus not be correct to state
that it is safe to reside on the site, a clear communication to that effect is needed to
explain the reasoning behind this political position.

maximal acceptable
exposure from
contaminated sites

Fig. 5.6 Maximum
acceptable exposure from
contaminated sites, as critical
exposure (aka: toxicological
reference value) reduced by
the (imposed) background
exposure that may not be
exceeded

0

(imposed) background
exposure

Toxicological
Reference Value