Predicting herbicide losses from hard surfaces: scenario characterisation and model concepts

The environmental impact of non-agricultural pesticides is currently assess ed by comparing available toxicological data with predicted environmental c oncentrations (PECs) assuming that 100 % of the applied compound is washed off the surface by a 25 mm rainfall event. Studies sponsored by a consortiu m of government and industrial bodies have provided data, which is being us ed to develop an exposure model for herbicide losses from hard surfaces. Tw o scenarios are modelled: A 10 ha urban catchment draining to a small strea m; a major road in a rural setting draining via gully pots to a small strea m. Fixed parameters have been set for rainfall amounts, characteristics of the receiving body, 'hard' and non-hard surface type and run-off characteri stics and herbicide application factors. A sub-model to predict the percent age of applied herbicide washed off each target surface has been developed based on results from 'field studies'. The only user inputs to the model ar e herbicide application rate, Koc and solubility.