Influence of vegetation on the environmental partitioning of DDT in two global multimedia models

Two multimedia models are used to investigate the effect of a vegetation compartment on the environmental partitioning of dichlorodiphenyltrichloroethane (DDT): a steady-state unit world model using global averages of vegetation cover and land-to-sea ratio and a dynamic model with latitudinal zones and zone-specific vegetation types and annual temperature courses. The vegetation compartment represents canopies of deciduous and coniferous forests and blades of grasses; the organic carbon content of the vegetation-covered soil is higher than in the bare soil. In the steady-state model, transfer from the air to the vegetation and the underlying soil as well as revolatilization from the foliage and reduced deposition to the soil is observed, depending on the chemical's degradation rate constant in vegetation and the deposition velocities of the gaseous and particle-bound fractions. In both models, a significant effect of the organic carbon content of the vegetation-covered soil increasing the effect of the vegetation compartment is observed. In the steady-state model, the changes in the DDT concentrations in air do not exceed 7% difference between the cases with and without vegetation; the soil concentrations differ by maximally a factor of 2.7. In the spatially and temporally resolved model, however, air concentration differences up to 90% are observed, depending on the type and amount of vegetation in the latitudinal zones. Long-range transport is less pronounced in the model with vegetation.