PARENT SESSION

1L - Exposure Modelling
Poster Hall
8:30 AM - Wednesday, 30 April 2003
Chair: Lammel, G.¹, ¹
Co-chair: Dachs, J.², ²

(WEP/86) Uncertainty analysis of PECs for pesticides in surface water modelling.

Fauser, Patrik¹, Thomsen, Marianne¹, Sørensen, Peter¹, Petersen, Søren ², Styczen, Merete², ¹ National Environmental Research Institute, Roskilde, 4000, Denmark² DHI Water & Environment, Hørsholm, 2970, Denmark

ABSTRACT- When models are applied in decision-making processes an evaluation of the uncertainty of the model predictions is crucial. Some kind of uncertainty analysis is needed before the model system can be assumed to have any predictive power. This study considers the catchment model MIKE SHE representing a drainage dominated sub-catchment (0.03 km2) of the Lillebaek catchment (4.4 km2) on Funen, Denmark. It is combined with a model describing quasi steady-state conditions in a stream, representing a typical segment of Lillebaek. When risk assessment of pesticides in surface waters is performed a conservative approach is to consider a worst-case scenario with respect to pesticide input to the recipient. Such a scenario can be described in a drainage dominated catchment study. Following application on the field, the time for transport in top soil and drain and appearance of concentration peak in the stream is in the size order of hundreds of days. The time for obtaining steady-state concentrations in bulk water and sediment is below one day. Therefore an analysis of the dynamic behaviour of the stream model is redundant when the stream receives substance from leaching through soil. The Predicted Environmental Concentrations (PECs) in the soil and surface water can be associated with large errors. These can arise from the partitioning and degradation coefficients for the pesticides and site specific parameters, such as the water-sediment exchange coefficient, derived in experimental studies. In a stochastic approach the influence of the variability of these parameters for 37 different pesticides is investigated on the fate behaviour in the soil and surface water.

Key words: Uncertainty, PEC, Surface water, Pesticides