OECD 302B: Inherent Biodegradability Test - Zahn-Wellens/EMPA Test
OECD 302B is an inherent aqueous aerobic biodegradation test that determines the inherent biodegradability of a material by measuring dissolved organic carbon or chemical oxygen demand. As one of the second-tier tests among OECD 301-303 standard methods, it is typically used for materials that are not readily biodegradable. The test normally lasts for 28 days, but the prolonged exposure of the test substance to microorganisms is allowed.
CONCEPT OF OECD 302 TESTS
As the second tier of tests in OECD standard methods for biodegradability evaluation, OECD 302A-C are designed to determine whether a material is inherently biodegradable.
Prolonged exposure of the test substance to microorganisms and a low ratio of test substance to biomass are allowed, which offers a better chance to obtain a positive result compared to tests for ready biodegradation.
Biodegradation percentages above 20% may be regarded as evidence of inherent biodegradability, whereas biodegradation percentages above 70% may be regarded as evidence of ultimate biodegradability. This indicates that the material is not likely to persist indefinitely in the environment.
If a sample does not pass the 70% threshold, it may lead to a preliminary conclusion of environmental persistency. The higher tier of tests OECD 303 may be performed to evaluate the degradation under environmentally realistic conditions, or an evaluation of the environmental effects of the degradation products may be performed.
