Introduction to Contaminated Site Management - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 53

(Swartjes et al. 2007 ), or the performance of bioassays in several tiers of the TRIAD
approach, to determine the site specific ecological risks (see Chapter 15 by Rutgers
and Jensen, this topic).
Finally, a third purpose of laboratory studies is validation of models or testing of
technologies (pilot studies). An example of a validation study is the comparison of
calculated with measured indoor air concentrations for 11 petroleum hydrocarbons
and chlorinated solvents sites in the USA and Canada (Hers et al. 2003 ).
In short, to enable Human Health and Ecological Risk Assessment, experiments
are simply a necessity. In principal, laboratory experiments for validating and test-
ing and, to a lesser extent, for assessing input parameters could be replaced by
field studies. However, the adage that 'field studies are always better than lab-
oratory studies' requires a few nuances. The choice for field versus laboratory
studies simply depends on the trade-off between the control of conditions in the
laboratory versus the degree of reality in the field. Of course, financial arguments
also must be included in this choice. Often a multitude of experiments can be
performed in the laboratory for the same budget as for one single field study.
Another, non-scientific, aspect that is in favour of field experiments is that they
better connect with public perception, but also even sometimes with scientific
perception.
1.7.5 Expert Judgement
It is a major inconvenience when in a scientific discipline the possibilities for a
quantitative analysis are lacking. In such a case, expert judgement may offer an
alternative. Expert judgement is the process in which experts determine an opin-
ion, (partly) based on 'gut feeling'. In an optimal expert-judgment process, several
experts are involved, and opinions are based on consensus.
A situation, in which expert judgement can be used, for example, is when a
Soil Quality Standard for a specific contaminant is lacking and effect data are not
available for this contaminant. Via expert judgement a 'substitute contaminant' with
similar physico-chemical contaminant characteristics can be selected, for which it is
expected that effects, and hence the Soil Quality Standard, are in the same order of
magnitude. Another example relates to the optimal balance between the use of a few
available measured contaminant concentrations for a specific vegetable and of many
less appropriate data for a non-edible crop, in terms of determining a representative
concentration for a specific vegetable.
In practice, expert judgement can vary from the opinion forming of a single
expert up to striving towards consensus within a group of appropriate experts. A
decent expert judgement must be performed within a well conceived group, that
often includes experts from different disciplines and, preferably, individuals who
approach the issue from a different angle. In any case, the risk assessor needs to
describe the expert judgement process and the decisions criteria that were used
so that scientists, regulators, and other stakeholders can decide how to weigh the
outcome of the expert judgement.