In today’s practice of authorization and regulation of chemicals (pesticides, biocides, pharmaceuticals) as well as in the evaluation of water quality criteria the center stage is still taken by the originally used chemicals (parent compounds). However, less persistent chemicals will be abiotically or biotically degraded in the environment without being fully mineralized in each case. These emerging transformation products are quite often more persistent and more polar and can therefore reach the aquatic environment more easily than the parent compounds. In some cases the transformation products are even similarly toxic or even more toxic than the parent compound (Figure 1).
