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Environmental fate & pathways

Biodegradation in water: screening tests

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Three biodegradation screening studies (BOD tests) are available for dipropylene glycol methyl ether acetate (DPMA). In addition two biodegradation screening studies for the structurally related compounds dipropylene glycol methyl ether (DPM) and propylene glycol methyl ether acetate (PMA) are available as supporting studies.

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The biodegradation of dipropylene glycol methyl ether acetate (DPMA) was investigated in three different studies: a modified ready biodegradation test (Dow, 1996), a MITI test (Dow, 2000) and a BOD test (Dow, 1983). The ready biodegradation of DPMA was assessed in a modified 301 D closed bottled test with pre-adapted inoculum. The O2 consumption reached 58% and 84% after 28 days inoculated with DPMA at 7.5 mg/L and 3.5 mg/L respectively, indicating a high potential for biodegradation. In another study (Dow, 1983), the BOD after 28 days was 67% of the ThOD in industrial inoculum, while 9% BOD was observed in municipal inoculum. In the third study (MITI test; Dow, 2000), the level of biodegradation was 12% after 7 days and 16% after 28 days. Analytical determination of the DPMA and its primary metabolite dipropylene glycol methyl ether (DPM) indicate a complete primary degradation of DPMA to DPM and acetate. The primary degradation most likely occurred in the first 7 days of the experiment when the greatest increase in BOD was observed, which is expected to relate to the complete degradation of acetate. The ultimate biodegradation of DPM was, however, not observed in this test system, despite DPM reaching the criteria for ready biodegradation when tested individually (Dow 1998). Based upon its structural similarity to propylene glycol methyl ether acetate (PMA), DPMA is not considered to be persistent. Both PMA and PM, the corresponding propylene glycol methyl ether, have shown rapid biodegradation. For example, rapid degradation of PMA to PM and acetate has been observed in 3 soil types. The degradation half-life of PMA was<1 day, with the subsequent degradation (i.e. mineralisation) of the formed PM within 3 days (Dow, 1995). Since DPMA is structurally similar to PMA, DPMA is expected to degrade to DPM and acetate. Complete primary degradation of DPMA to DPM and acetate was observed in the MITI test (Dow, 2000). Once DPM is formed, full mineralisation can be expected as DPM has been shown to be readily biodegradable in the OECD 301F Manometric Respirometry test. The test methodology used does not allow the conclusion that DPMA is “readily degradable”. However, based on the high levels of biodegradation observed in a modified ready biodegradation test with pre-adapted inoculum and the rapid primary degradation of DPMA to DPM, DPMA can be classified as “inherently biodegradable fulfilling the criteria”.