Investigating the global fate of DDT: model evaluation and estimation of future trends.

The global environmental fate model CliMoChem has been used to calculate concentrations of dichlorodiphenyltrichloroethane (DDT) and its degradation products in the environment. To this end, best available physicochemical properties of DDT have been assembled, and a realistic DDT emission scenario covering the period from 1940 to 2005 has been generated. Results from the model are temporally and geographically resolved concentrations of DDT, dichlorodiphenyldichloroethylene (DDE), and dichlorodiphenyldichloroethane (DDD) in various environmental media. To confirm model results with measurements, we have developed a method for a qualitative and quantitative comparison of model and measurements. The agreement between the model and measurements is good, especially in the temporal dimension, and in the soil and air compartments. Using estimated DDT emissions for the future, we predict environmental concentrations in the next 50 years. The results show that, if emissions continue at a low level, concentrations will decrease by a factor of 30 in temperate regions and by a factor of 100 in the Arctic, as compared to the concentrations in the 1960s and 1970s. In the tropics, levels decrease by a factor of 5 to 10, only. Whereas environmental concentrations and estimated future emissions are at steady state after about 10 years in temperate and tropical regions, this takes over 50 years in the Arctic.