STANDARDIZED BIODEGRADABILITY TESTS - EXTRAPOLATION TO AEROBIC ENVIRONMENTS

Assessing the risk of chemicals for the environment requires an estima tion of degradation rates in order to evaluate a realistic exposure co ncentration for organisms. As QSAR's (quantitative structure activity relationships) for degradation are far from generally applicable, meth ods are proposed to extrapolate results obtained from standardized deg radation tests to the most relevant environmental compartments. The de sign of the OECD laboratory test methods is such that, at least at the screening level, almost general applicability is achieved. Inevitably , tests conditions do not reflect biodegradation in the real world. Ho wever, if data are available on biodegradation it appears that, for mo st chemicals, references are made to one of those standardized OECD me thods. A systematical procedure to translate the result of an OECD tes t (or a combination of test results) to transformation rates under rea listic circumstances is still lacking. In this report a methodology is presented to evaluate standardized test results in terms of rate cons tants for degradation in a biological waste water treatment plant, sur face water and aerobic soil. The extrapolation of a positive result in OECD screening tests relies a.o. on the assumption that the half-life is inversely proportional to the total concentration of micro-organis ms. A first attempt was made to validate this extrapolation by compari ng results of reported field studies on biodegradation of 20 chemicals with positive results in OECD Ready Biodegradability tests.