Report No SR3714

IMPACT OF PESTICIDES ON RIVER ECOLOGY

SR3714

Sep 1994

EXECUTIVE SUMMARY

Due to the demands of the EC Drinking Water Directive (CEC 1980) research on pesticides in the environment is currently focused on chemicals that are most likely tO be found at high concentrations in the water column. However, these chemicals are not necessarily the most hazardous to riverine biota. There is an urgent need to assess the ecological importance of pesticide contamination in UK rivers, particularly from diffuse applications to land. This study forms the first phase of an anticipated three-phase programme of work to investigate the impact of currently-used agricultural pesticides on riverine communities. The main aims of this phase were to assess the extent of current knowledge and to outline the work required for the next phase, which would involve the development of risk assessment methods (the final phase would involve the monitoring of field effects). Phase 1 work has linked closely with parallel work being undertaken in England and Wales on behalf of the National Rivers Authority.

A computerised search of the published literature has been conducted, focusing on studies undertaken in real or environmentally realistic conditions. This revealed that few relevant studies have been conducted and most of these relate to the effects of insecticides on macroinvertebrate communities. For some pesticides, significant ecological effects have been detected at concentrations likely to arise from normal usage, giving cause for concern about other pesticides that have been given little or no attention in field situations. The toxicity of sediment-bound pesticides and of pesticide additives or carriers have rarely been addressed in either laboratory or field situations. The effects of breakdown products and mixtures of pesticides have also received little attention. Quantitative Structure Activity Relationship (QSAR) models show promise in terms of predicting the effects of pesticide mixtures, but many pesticides which are currently used have specific modes of action that hamper such predictions. For this reason, QSARs are unlikely to be able to predict the combined effects of such chemicals in the short-term.

Consultations with River Purification Boards and the Department of the Environment (Northern Ireland) biologists identified over 20 catchments where impacts from currently-used agricultural pesticides are suspected, despite present monitoring methods not being geared towards the detection of insidious effects. Residues of prohibited persistent pesticides, such as DDT, are suspected of causing biological impacts in several areas, possibly due to gradual release from soils into watercourses.

Future research needs to identify areas at highest risk from pesticide pollution, at both low (national/regional) and high (within-catchment) resolutions. Specifications for risk assessment tools at both resolutions have been produced, in conjunction with NRA research. It is recommended that these tools are now developed and that research into field effects is subsequently undertaken in high risk areas. This research should be aimed at identifying areas where preventative measures are most needed, and at the identification of pesticides currently in use that may need to be reviewed by the Product Licensing Committee.

KEYWORDS: Pesticides, agriculture, river, ecology, diffuse pollution

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