The use and risks of agricultural pesticides will continue. It is proposed here that better control and possibly some prevention of environmental and health problems should replace the arbitrary standards and post- event monitoring that are still current practice. Mathematical models have been developed for atrazine in a characterized soil from outside Ottawa, Ontario. Experimental data obtained bythe on line HPLC microextraction method were used for the development of the models. The labile sorption sites were treated as a reactant and the number of sites per gram of soil was used to define stoichiometry. This allowed a second-order kinetics integral rate law to be used for sorption from solution onto labile sorption sites, and a first order kinetics integral rate law to be used for bound residue formation. An experimental check and error analyses indicate that the type of model can be used for predictive calculations. The physical meaning of the distribution coefficient K(D) is also considered. The model suggests some practical implications for leaching through soil and for transport by storm runoff. The type of model would be best used for providing input data for fate and transport hydrology models.