The GeoPEARL model. Description, applications and manual

Set up to simulate the behaviour of a wide range of pesticides (e.g. volatile substances and substances showing soil-dependent sorption constants and transformation rates), GeoPEARL plays an important role in the evaluation of such Dutch pesticide policy plans as the 'Multiyear Crop Protection Plan' and the plan for 'Sustainable Crop Protection'. The report contains a number of examples of applications using pesticides with different properties. Generally, results showed the average fluxes of pesticide into local surface waters to be higher than the average fluxes of pesticide to the regional groundwater, with rapid drainage mechanisms (i.e. tube drainage and surface drainage) dominating.

These observations should be taken seriously, since pesticides lost through these routes contaminate local surface waters directly. GeoPEARL has also been used to verify the current Dutch Pesticide Authorisation procedure. This procedure starts by applying PEARL to a single site, which, for leaching, is assumed to represent realistic worst-case conditions. Results of GeoPEARL showed, however, that the leaching potential of individual pesticides peaked in different regions, indicating that no such single site exists. The conclusion was that the single-site approach could give erroneous results, unless additional precautionary measures were taken while selecting the pesticide input parameters. Discussion on what these conditions should be can be avoided by opting for direct application of GeoPEARL in preference to the single-site approach.