Assessing the degradation of chemicals in drinking water resources

Recommendations for conducting a simple and "cold" degradation test according to OECD TG 309 with substances found in water resources

Dictionary explanation of the word "persistence"

The most problematic intrinsic substance property

For many substances detected in water resources there is no conclusive assessment of their intrinsic degradability. In cooperation with the German Federal Environmental Agency, TZW has developed recommendations for a simple and cost-effective implementation of a valid "cold" degradation test according to OECD TG 309.

The threat to drinking water resources posed by persistent and mobile substances has been recognized for decades. Lack of or insufficient intrinsic degradability (persistence) is scientifically considered to be the most problematic property of a chemical. It leads to accumulation in the environment and prevents degradation of the contaminant even when emissions cease. This increases exposure and the likelihood of effects occurring and makes quantitative risk assessment impossible. However, for many substances, some of which have been detected in water resources for decades, there is still no conclusive assessment of their intrinsic degradability in the aquatic environment by the companies responsible. However, it is essential for water utilities, monitoring and regulatory authorities to know whether the chemicals detected in their own water resources are persistent and therefore pose a threat to drinking water production.

If the suspicion of lacking or insufficient intrinsic degradability of a chemical of limited relevance to soil or sediment has not been ruled out in the screening test, ECHA recommends as a standard that the OECD TG 309 degradation test should always be performed first. The aim of this degradation test is to demonstrate intrinsic aerobic biodegradability and to derive a valid aerobic biodegradation half-life (DegT50) in surface water. A valid result may be obtained without 14C labeling of the test substance (so-called "cold" test). Analytically, this requires only the quantification of the test substance itself and only in the aqueous phase. This is especially expected for persistent and mobile chemicals. By eliminating the need for 14C-labeling of the test substance, a valid degradation test according to OECD TG 309 can be performed easily, cost-effectively and efficiently by water suppliers and authorities with appropriate laboratory infrastructure and established analytical methods for substances found in their own water resources.

On behalf of and in cooperation with the German Federal Environmental Agency (Umweltbundesamt - UBA), recommendations for a simple and cost-effective implementation of a valid "cold" degradation test in accordance with the OECD TG 309 test guidelines have been developed in the form of an expert report. The recommendations apply only to those test substances for which no pronounced and significant decrease in concentration in the aqueous phase is expected during the test and are intended to facilitate the performance of such a degradation test for substances in their own water resources by a wide range of users. The recommendations aim at selecting the test conditions (temperature, concentration range of the test substance, inoculum) in such a way that standardized, generally valid, comparable and environmentally relevant results are obtained for the test substance.

The published report also presents the criteria that must be met for a chemical to be potentially suitable as a test substance for a "cold" degradation test according to OECD TG 309, as well as a list of 832 substances prioritized for such a test that have been detected in water resources.

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