Developing Methods to Predict Chemical Fate and Effect Endpoints for Use Within REACH

Abstract

Abstract:With the pending implementation of REACH, both old and new chemicals will have to be registered and chemical safety reports will have to be compiled. Depending on the yearly tonnages produced or imported, (eco-) toxicological and chemical fate data of varying degrees of detail will have to be produced. It has been forecast that these new requirements will result in higher costs for registration and an increased need for animal testing. Some of this additional workload could be avoided by making use of in vitro or in silica prediction methods. At Eawag (Swiss Federal Institute of Aquatic Science and Technology) several research groups are working on the development and validation of quantitative structure-activity relationships (QSARs) and related methods to predict ecotoxicological and fate endpoints, such as reactivities in or partitioning between different environmental media, based on chemical structure or easily measurable physico-chemical properties. When developing such tools, special attention has to be paid to use only descriptors whose mechanistic significance for the modelled endpoint is well understood on a molecular level. In this article four examples of our work in the field of compound fate and effect predictions will be presented: i) the measurement of compound descriptors for use in linear-free-energy relationships to predict partition coefficients between environmental media; ii) the development of free-energy relationships for the prediction of indirect photolysis; iii) the evaluation of existing structure-biodegradability models to predict soil biodegradation half-lives; and iv) the application of mode-of-action-based test batteries to develop quantitative structure-activity relationships to classify chemicals according to their modes of toxic action.

Oxidation of Aquatic Organic Contaminants Induced by Excited Triplet States

“…The Marcus and Rehm-Weller equations, as applied to the triplet-induced oxidation of phenols, [30] are promising tools to assess electron transfer rates from, and finally oxidation rates of organic contaminants in aquatic systems. Owing to the ubiquity of the hydroxyl radical in sunlit and UV-irradiated waters, a relevant contribution of excited triplet state oxidants to contaminant degradation is limited to those reactions occurring at relatively high rates [33] (second-order rate constants higher than ≈ 10 7 M − 1 s − 1 ). Once a compound has been identified as potentially highly reactive to 3 CDOM*, the effectiveness of its oxidation should be checked.…”

Comparison of different probe molecules for the quantification of hydroxyl radicals in aqueous solution

“…The fate of organic pollutants depends on both biological and chemical processes, the latter playing a substantial role into the transformation of biorefractory compounds, including some pesticides and pharmaceuticals. Among the chemical transformation processes, photochemistry has often an important role in defining the fate of pollutants Fenner et al 2006).…”

Quantification of singlet oxygen and hydroxyl radicals upon UV irradiation of surface water

“…The cited reactions induce the transformation of dissolved compounds including manmade xenobiotics, limiting their persistence in the aquatic systems. However, such processes can also yield harmful secondary pollutants (Fenner et al 2006;Lam and Mabury 2005;Vione et al 2004). …”