For a number of years, the Waste Research Unit of the Harwell Laboratory has been conducting research on the codisposal of industrial waste and municipal refuse as a practical and environmentally acceptable disposal option. Codisposal depends on utilizing the attenuation capacity of the refuse, and involves mechanisms such as dilution, biodegradation, adsorption, and precipitation.

To make a closer comparison with a codisposal site, laboratory-scale landfill experiments have been designed with the aim of studying the behavior of pesticide wastes. Four pesticides were selected for investigation, namely lindane, pirimiphos-methyl, (4-chloro-2-methylphenoxy) acetic acid (MCPA), and atrazine. Leachate monitoring revealed that the migration of MCPA, atrazine, and pirimiphos-methyl through municipal wastes was closely related to their solubility in water. The results for lindane are not yet available. The attenuative capacity of the refuse was investigated by comparing the concentration of pesticide in leachate immediately below the layer of pesticide waste and at the base of the column. Significant attenuation of MCPA and atrazine was observed.

The use of destructive sampling produced additional information in relation to attenuation, the effect on landfill microflora, and persistence of the pesticides under landfill conditions. The marked persistence of pirimiphos-methyl, a pesticide normally considered to be short-lived under agricultural conditions, illustrates that predictions based on extrapolation from agrarian practice are misleading. The results emphasize the importance of laboratory-scale experiments in the study of landfill science.