Probabilistic ecological risk assessment of secondary poisoning from DDT

Sammanfattning: Although prohibited since decades, dichlorodiphenyltrichloroethane (DDT) and its metabolites still remain in the soil and pose a threat to ecosystems, where especially birds are susceptible to toxic effects. In this thesis, a model developed in the 1990s was used and updated in order to estimate the risks of DDT to top predators at a forest-plant nursery site. Unusually high concentrations of DDT have been found at this site and it was therefore of interest to evaluate the potential ecological effects. The model used deals with the fact that species without direct contact with the soil are still exposed to soil contaminants through their prey, a phenomenon called secondary poisoning. Bioaccumulation factors, toxicity data and species-specific diet were combined in order to quantify the maximum permissible concentration in soil (MPC). MPC5 is regarded as the acceptable level, where 95 % of the populations are protected. Red kite, sparrow hawk, kestrel, badger and weasel were selected as species of concern. This study shows that given the soil concentrations of DDT at the site, the risk (probability) of exceeding MPC5 is high, especially for red kite and sparrow hawk. Matter of fact, the probability of exceeding MPC5 for any of the species considered are >64 %. The concentrations of DDT in soil found at the forest-plant nursery are therefore unacceptable for the protection of birds and beasts of prey.