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Environmental fate & pathways

Biodegradation in water: screening tests

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For ready biodegradability, key studies are Schwarz (2009) and Yakabe (1994). The former study is of the higher quality as it is fully documented with a GLP certificate. Caspers et al (1986) and BASF (1988) are key studies, of similar quality, with respect to the determination of inherent biodegradation. The Baumann (1986) coupled units (simulation test) study is a good quality key study.

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Results from the ready biodegradation studies clearly indicate that MDA is not readily biodegradable. In the Schwarz (2009) study 0.5mg/l radiolabeled MDA was used in the OECD 301B test. At this very low concentration of test substance and where inhibition of the microbial population would not be expected, only 46% biodegradation was recorded after 28 days exposure. The Yakabe (1994) study confirmed that MDA is not readily biodegradable in the OCED 301F test.

In the Caspers et al (1986) study using activated sludge from a predominantly municipal source, the inherent biodegradation of MDA was found to be only 43% after 28 days. In a further inherent biodegradation study (BASF, 1988), using activated sludge from an industrial wastewater treatment plant, MDA was found to undergo 95% degradation after 14 days, and 97% after 21 days.

A Coupled Units Test (OECD 303A, Baumann 1986) with activated sludge produced from a mixed inoculum (secondary effluent, Rhine-water, suspension of garden soil) with an adaption phase of 25 days indicated only 6.5% biodegradation after 34 days.

These results clearly show that 4,4'-MDA is not readily biodegradable and fulfills the criteria for inherent biodegradation only if an adapted industrial inoculum is used. From the Coupled Units Test it can be deduced that an adaptation time of 25 days is not sufficient. Therefore 4,4'-MDA has to be considered as inherently biodegradable in industrial wastewater treatment plants (wwtps) only. Degradation in municipal wwtps cannot be deduced from these results.

On the basis of available biodegradation tests it is not possible to conclude that the substance is biodegraded under environmental conditions.