Advances in comparative analysis of adverse effects in aquatic ecosystems with emphasis on studies with humic substances and on progress in mathematical analysis techniques

Standard evaluation procedures of hazardous chemicals in the environment are not able to identify mechanisms of alterations of potentially harmful effects, for example in the presence of organic geochemical matrices. By including aquatic humic substances into standard Daphnia and fish tests we found that the bioconcentration of organic chemicals is reduced in many instances. Furthermore, decreases as well as increases in toxicity of substituted phenols and anilines can occur. Some environmental chemical mechanisms that can alter the toxicity of parent compounds are discussed, but the mechanisms are not yet identified. At present, there does not appear to exist a common mechanism for the alteration of toxicity. As a consequence, techniques of comparative analysis of adverse effects should be applied on a phenomenological basis. An appropriate technique is based on Hasse-diagrams, which are graphical presentations of so-called partially ordered sets. Such a generalized order is necessary, if for example chemicals are to be described by more than one characteristic quantity. In the methodological section, the Hasse-diagram technique is explained in detail with exposure data of a German river. A very simple deterministic model, EXWAT, is applied to get a set of scores for each of nineteen chemicals found during measurements in the River Main. By EXWAT the environmental fate of these chemicals is described by four descriptors. The Hasse-diagram shows that there are four classes of chemicals that have a different pattern of their fate-descrptors and have the highest priority with respect to environmental impact. Examples of how to read Hasse-diagrams are given. This technique, however, is not limited to exposure data only, but can also be successfully applied to effect data as well as to a combination of exposure and effect data. The application to effect data will be demonstrated with the above-mentioned data on humic substances mediated alterations of xenobiotics toxicity.