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Environmental fate & pathways

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Results from the ready biodegradation studies clearly indicate that MDA is not readily biodegradable. 0.5mg/l radiolabeled MDA was used in an OECD 301B test (Schwarz, 2009). 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 is rapidly eliminated from water only if an industrial inoculum is used. From the Coupled Units Test it can be deduced that an adaptation time of 25 days is not sufficient. Therefore elimination of 4,4'-MDA from the water body has to be considered as relevant in industrial wastewater treatment plants (wwtps) only. Degradation in municipal wwtps cannot be deduced from these results.

To further investigate the fate of the test substance in surface water as well as in water/sediment systems studies according to OECD 309 and OECD 308 were performed. The results of those studies indicate that the test substance rapidly disappears from surface waters with half-lives of maximum 11.1 days whereas the maximum half-life in sediments was determined to be 21 days (under anaerobic conditions). In the presence of sediments the 14C-labeled test substance migrated to the non-extractable fraction of the sediment. The parent compound disappeared in the process of an OECD 309 study completely while several metabolites were detected. The mineralization of the test substance was determined to be low under the conditions of both studies with maximum values of 5.7% in an OECD 308 study and 25.5% in an OECD 309 study (both values based on the production of 14CO2).

The results of the conducted degradation tests demonstrate that 4,4'-methylenedianiline is not readily biodegradable and not inherently biodegradable under domestic conditions, but it is removed from surface waters within days either by mineralisation or transformation and migration into sediment. Hence, the test substance itself is not considered to be persistent in the environment.