Thematic maps for regional ecotoxicological risk assessment: pesticides

Frequently, decisions and/or recommendations on various regional scales on the application of pesticides have to be made by authorities, institutions and individual persons. Therefore, it is advisable to identify and rank the ecotoxicological risk of a pesticide under special consideration of the respective regional conditions. As a result thematic maps can be designed identifying and ranking different vulnerable regions with respect to groundwater contamination, permeable soils and areas at high risk for terrestrial and aquatic organisms. Also, different pesticides can be ranked with respect to their ecological risk for a specific area under consideration. Such a ‘regionalization’ of the ecological risk can be approached as follows: (1) Small-scale scenarios being representative for the regions under consideration have to be selected and characterized. The characterization has to comprise: soils (types, genesis, thickness, permeability to subsoils), topology (e.g., slope), climatic conditions, surface water (occurrence of ditches, ponds and creeks), portion of the drained area, portion of land under agricultural use, typical cultures and types of pesticides, application rates and frequency. (2) The representativity of the selected scenarios for the region under consideration has to be determined. (3) For the various regions predicted environmental concentrations (PEC) are assessed for the different paths of entry (mainly spraydrift and runoff), the different ecological systems, the different durations of the impact (fate consideration). If appropriate, sensible average values (e.g., for an average distance of the aquatic system from the target area) have to be agreed upon. (4) Determination of concentrations of no environmental concern (NEC). (5) Formation of risk quotients (PECi/NECj) for the each path of entry, ecological system and duration of the impact and subsequent aggregation of the quotients on a previously defined scale. The result is not an absolute risk, but the ranking of the regions as stated above can easily be performed.