Effect-directed analysis of transformation products in drinking water treatment

In Switzerland more than 30’000 chemicals are used in everyday life, whereas for only a minority of these substances an environmental or human based risk assessment is available and only a small number of substances are currently regulated by (drinking) water laws and guidelines. Some of these substances can be found in natural water resources that may eventually be used for drinking water purposes. If water is treated by advanced oxidation processes (AOPs) such as ozonation, UV irradiation, O3/H2O2 and UV/H2O2, these substances may be degraded or transformed to a variety of different transformation products, for which in most cases the structure and toxicity are not known.

Up to now only a limited number of contaminants and toxic endpoints relevant for human health have been systematically studied. In a current project between Eawag and the University of Colorado at Boulder (Linden Research Group), funded by the Water Research Foundation and the Federal Office for the Environment (FOEN), the toxicity of transformation products formed by AOPs of selected chemicals from the contaminant candidate list (CCL3) of the US Environmental Protection Agency is being investigated.

Because the processes involved in advanced oxidation processes lead to the formation of a cascade of degradation products, the identification of all of them is a tedious and expensive procedure. As an alternative, an effect-directed approach allows the priority setting for further identification of toxic compounds. The toxicity of the samples taken during the degradation processes is directly measured and specific transformation products are identified only if any increase in toxicity is observed (image). Such a methodology can determine whether the degradation products “retain” the toxicity of the parent compound or whether the degradation lead to a formation of products possessing another kind of toxicity. The testing procedure in this study involves the determination of the genotoxic and estrogenic activity by suitable in vitro bioassays.

Bioassays, such as cell-based assays, are currently finding their way into water quality assessment. An excellent overview and description of bioassays or bioanalytical tools for water quality assessment can be found in the book “Bioanalytical Tools in Water Quality Assessment”.

Image: effect directed approach to identify toxic degradation products
Image: effect directed approach to identify toxic degradation products