Strongly adsorbing pesticides (SAPs ) have been regarded as immo- bile in soils. However, recent findings indicate that SAPs can be transported long distances, presumably because they are bound to, and transported by colloidal particles that are suspended in the water percolating down through the soil profile. Thus, SAPs repre- sent an unexpected long-term threat to the environment. The objec- tive of the proposed research is to study the risk of groundwater contamination by SAPs. This will be accomplished by measuring the kinetics of long term adsorption- and desorption reactions with a natural isolated colloidal fraction, and by studying the trans- port of these carrier colloids through macroscopic undisturbed soils. The results will be combined in a macroscopic transport mo- del, to allow for quantitative risk assesment. The applicant will both contribute with his expertice and receive extensive training while-performing this work at the Danish Institute of Plant and Soil Science. Results can be used to develop new criteria for pesticide approval and groundwater quality monitoring.