A probabilistic model for deriving soil quality criteria based on secondary poisoning of top predators. II. Calculations for dichlorodiphenyltrichloroethane (DDT) and cadmium.

A simplified food web with three trophic levels is designed: plants and invertebrates at the first, small birds and mammals at the second, and birds and beasts of prey at the third trophic level. Exposure of top predators via separate food chains is analyzed. However, most top predator species are exposed via more than one food chain (food web). Therefore, a species-specific approach is followed too, for which four bird of prey species and two beast of prey species with different food choices are selected: sparrow hawk, kestrel, barn owl, little owl, badger, and weasel. The most critical food chains for secondary poisoning of top predators are soil --> worm/insect --> bird --> bird of prey for dichlorodiphenyltrichloroethane (DDT), and soil --> worm --> bird/mammal --> bird of prey for cadmium (Cd). The risk for the selected top predator species is much lower than the risk based on these critical food chains because the critical food chains constitute a minor part of their food webs. Species feeding on birds (sparrow hawk) and small carnivorous mammals (barn owl) are exposed to DDT and Cd to a much higher extent than species mainly feeding on small herbivorous mammals (kestrel and weasel). It is recommended to include exposure via the pathways soil --> worm/insect --> bird/mammal --> top predator in procedures for derivation of environmental quality objectives for persistent and highly lipophilic compounds.