ABSTRACT
The ecosystem in its natural context is the most important level for ecotoxicological issues, although tests at the population level are obviously easier to conduct. In contrast, the number of field studies devoted to examining the fate or effect of different chemicals at various sites with respectively individual methods and priorities is so great as to be almost unmanageable. Otherwise, due to the complexity of the subject of investigation and the resulting expense, only very few field tests are regularly required in the framework of registration procedures, and even fewer have been standardized. Special attention is devoted to the size of the test surfaces, since effects determined for mobile organisms may soon be offset by recolonization if the test area is too small. Therefore, a variety of monitoring studies are described in the following subsections according to the environmental medium in which they are conducted.
