Modelling the behaviour of organic chemicals in soil and ground water

The development, testing and application of computer models for the behaviour of organic chemicals, especially pesticides, in soil and ground water has been reviewed. Detailed data are needed on the structure and properties of the soil and ground‐water systems, and on the flow of water through these systems. Adsorption and transformation of organic chemicals can be studied in the laboratory and the results introduced into the models. The mathematical techniques most frequently used for the solution of the differential equations are briefly discussed. Some models for the behaviour of pesticides in the root zone have been tested against results of field trials and some interesting deviations between computations and measurements emerged. Techniques for the simulation of the behaviour of organic chemicals in the ground‐water zone are also available. However input data for the models are often lacking, as are also results of field studies for testing the models.