Intercomparison programme on detecting biodegradability of chemicals in water: Final report prepared in July 1979 for the Environment and Consumer Protection Service of the Commission of the European Communities

Abstract

Ecotoxicological testing of chemicals should be harmonized in the countries of the European Communities. In this framework, an interlaboratory study of methods for testing biodegradability in water was undertaken. Two test methods were selected: the OECD Screening Test modified for dissolved organic carbon (DOC), and the Zahn-Wellens Test by DOC and chemical oxygen demand. Three test materials were investigated: tetrapropylenebenzenesulfonate (TPBS), diethylene glycol, and 4-nitrophenol. From the experimental data of 28 participating laboratories, some critical points of the methods were detected, and conclusions were drawn for improvements. Both methods are applicable for biodegradability testing but results from different laboratories may differ seriously. Such discrepancies are mainly due to different inoculum compositions. A high diversity of species is desirable. Furthermore, longer test durations are recommended, and the whole biodegradation curve should be examined instead of using only one value after a fixed test duration. Use of appropriate biodegradability standard materials should improve essentially the comparability between different laboratories. TPBS is scarcely degradable, diethylene glycol is degradable but often requires an adaptation period, and 4-nitrophenol is problematic by its toxicity, but obviously degradable by certain microorganisms.