Report No DWI0718

May 1995


Pesticides are used widely in agricultural and non-agricultural situations in the UK. Some pesticides are persistent in the soil and are leached into surface waters and groundwaters, including those which are abstracted and treated for public drinking water supplies. The maximum permitted concentration of individual pesticides in drinking water 0.1g/l is specified in the Water Supply (Water Quality) Regulations 1989. Special (and expensive) treatment of contaminated source waters is often required to achieve this stringent limit. In August 1992, the Department of the Environment awarded a contract to WRc plc and Gould Rural Environment Ltd (Reference PECD 7/7/415) for a joint study of pesticide use and treatment, supervised by the Drinking Water Inspectorate. The purpose of the study was to investigate the relative economic costs of preventing pesticide contamination using a range of pesticide control mechanisms and installing processes for pesticide removal at water treatment works.

Benefits related to the reduction of pesticide concentrations in the environment, for example for the protection of aquatic life, were not studied.

Four specific pesticide control scenarios were studied in detail using case studies on two sources of drinking water: a surface water (River Leam, Warwickshire) and a groundwater (Colne Valley, Hertfordshire). The control scenarios were:

Other control methods (restrictions in timing of pesticide applications and the substitution of environmentally-friendly pesticides) were also examined but were not considered to be currently feasible and therefore not studied in detail.

Current agricultural land usage and cropping patterns, pesticide application and environmental occurrence data were obtained for the two catchments studied. Future land usage, cropping patterns and pesticide applications in agricultural and non-agricultural sectors were projected for each scenario for the ten-year period 1992-2002. Mathematical pesticide fate models were used to calculate future pesticide concentrations in the river and groundwater resulting from predicted pesticide applications. The costs of water treatment (by adsorption on granular activated carbon and/or ozonation) to reduce the predicted levels of pesticides to the prescribed level for drinking water were calculated from water treatment models.

The main conclusions to be drawn from the case studies are as follows:

The use of levies and tradeable permits as economic instruments to control pesticide usage was reviewed. Product levies appear to satisfy the criteria for effective economic instruments in pollution control.

The methodology required to extend the study to all of England and Wales is discussed. A less detailed analysis, concentrating on establishing the marginal costs of pesticide restrictions and the agro-economic implications, is recommended.

The limitations to the study and its conclusions are discussed. These are principally:

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