PESTICIDE TRANSPORT TO SURFACE WATERS WITHIN AN AGRICULTURAL CATCHMENT

This paper presents data on the distribution of seven pesticides in an agricultural catchment which is located within the Agricultural Devel opment and Advisory Service farm at Rosemaund, 11 km north-east of Her eford, UK. Data for aldicarb, atrazine, carbofuran, dimethoate, MCPA a nd isoproturon, are available for both the soil and surface waters (dr ain and stream water), with simazine data available only for the strea m. Measurements were taken before and after pesticide application, whi ch was made following normal agricultural practice. Soil residue data showed the degradation rates of the pesticides to be within the range of literature values. Pesticide levels in the stream and drains during runoff events following rainfall ranged from below detection limits ( typically 0.02-0.1 mu g/l), to 264 mu g/l (for carbofuran). Over 90% o f the events had detectable maximum concentrations. The percentage of pesticide applied, which was removed during individual rainfall events , was calculated. The maximum value estimated was 1.1%, again for carb ofuran. Most of the events gave values several orders of magnitude bel ow this value. The data have been used to try to validate a range of m odels which could be used for screening new pesticides or for informin g decisions on the use of existing pesticides. The results of the vali dations are summarized.