Introduction to Ecological Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 610

a high accumulation affinity such as metals, Polycyclic Aromatic Hydrocarbons
(PAHs) and other hydrophobic compounds) that have been taken up by the organism
lower in the food chain. The consequence is that the organisms that are highest in
such a food chain can experience bioaccumulation , that is, accumulation of contam-
inants in their tissue although these organisms often do not have a direct relationship
with contaminated sites.
In fact, all above-ground animals can suffer from secondary poisoning, since her-
bivores consume potentially contaminated plants and carnivores consume animals
that might be exposed to contaminants from soil. However, the most relevant cases
of secondary poisoning relate to specific higher organisms that feed on worms (for
example, badgers) and rodents (for example, birds of prey).
Although scarcely used, food web modelling (e.g., Luttik 2003 ) offers a tool
for assessing the risks from secondary poisoning, mainly useful for site-specific
Ecological Risk Assessment. Traas et al. ( 1996 ), for example, presented a secondary
poisoning model for the kestrel and the barn owl. However, the resulting Ecological
Risk Assessment is very sensitive to the relatively uncertain calculation of the bioac-
cumulation and the transfer of the contaminants within the food web (Traas 2004 ).
Food web modelling counterbalances two of the great demerits of Ecological Risk
Assessment: firstly, the focus on effects for a single species, or at best for a small
number of species; secondly, the fact that differences in sensitivities to contaminants
among species are often neglected. Food web approaches provide an opportunity
to address the effects of contaminants at the level of an ecosystem. Alternatively,
hybrid food web/population models, which combine food web models and popu-
lation models, can be used for Ecological Risk Assessment at the population level
(Van den Berg et al. 1998 ).
Food web modelling could also lead to the identification of indicator organisms
that are representative for the functioning of a specific soil ecosystem. In princi-
ple, it is possible to derive Soil Quality Standards on the basis of food webs and
the existing feeding relationships between the different species in the food web.
This, however, requires a completely different approach in derivation of Soil Quality
Standards.
The statements in the previous section on the quality of food produced in agri-
cultural areas can be seen as an example of potential secondary poisoning due to the
soil quality.
13.7.5 Wildlife Protection
In less densely populated countries where larger natural areas are present such
as the US, Canada, Australia and Africa, wildlife is often considered as an eco-
logical protection target. Larger animals often are vulnerable to exposure from
contaminated sites, via bioaccumulation in the food chain ( secondary poisoning ,
see Section 13.7.4 ). Therefore, mainly contaminants with a high accumulation affin-
ity such as metals, PAHs and Polychlorinated biphenyls (PCBs) are a threat to
wildlife.