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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

There are reliable biodegradation in water studies for DMDMH, but there is a reliable water degradation study available for the hydrolysis product, DMH.  A reliable study (Mead 2001) determined that DMDMH was degraded 78% within the 10-day window and the test substance can be considered readily biodegradable. Additional studies with the degradation product showed that DMH is also readily biodegradable. Consequently, the test substance and its hydrolysis product are considered readily biodegradable in the aquatic environment.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

There are reliable biodegradation in water studies for DMDMH. There is also a reliable water degradation study available for the hydrolysis product, DMH.   Due to the rapid hydrolysis of DMDMH to DMH studies conducted with the hydrolysis product, DMH, are considered relevant for environmental fate and ecotoxicology and are considered in this dossier.

 

Mead (2001) conducted a reliable (Klimisch 1) GLP compliant study following OECD 301A methods. The biodegradability of DMDMH exposed to microorganisms derived from activated sludge was investigated under aerobic exposure conditions. Based on dissolved organic carbon (DOC) removal, at the end of the 10 day window the test material attained 78% degradation. At the end of the 28 day period the test material attained 95% degradation. The 10-day window validation criterion was satisfied and hence the test material can be considered to be readily biodegradable.

 

A reliable (Klimisch 1) GLP compliant study by Clarke (2007) followed OECD 301B methods. The biodegradability of DMH, the hydrolysis product of DMDMH, exposed to microorganisms derived from activated sludge was investigated under aerobic static exposure conditions.The biodegradability, based on CO2evolution, of DMH was determined to be 87% after an incubation time of 28 days. At the end of the 10 day window the test material attained >60% degradation; therefore, the 10-day window validation criterion was satisfied and hence the test material can be considered to be readily biodegradable.

 

Mulberry (1986) conducted a reliable (Klimisch 2) GLP compliant study following Ready Biodegradability: Modified OECD Screening Test’; 40 CFR 796.3240 methods. The biodegradability of 2.1322 mg/ml of DMH, the hydrolysis product of DMDMH, exposed to microorganisms derived from a mix of soil inoculum, activated sludge and surface water was investigated under aerobic exposure conditions. Based on dissolved organic carbon (DOC) removal, at the end of the 10 day window the test material did not meet the requirements of % degradation and validation criteria were not met indicating the test substance is not readily biodegradable. However, due to the nature of the test system (i.e. using a mixture of inoculum), the chance for adaptation and acclimation is minimal since the sole source of carbon and energy for microorganisms is the test compound. Therefore, since a low level of biodegradation was found it does not necessarily mean that the compound is not biodegradable under actual environmental conditions.

 

Pence (1986) conducted a reliable (Klimisch 1) GLP compliant study following EPA 40 CFR 796.3340 methods. The inherent biodegradability of DMH, the hydrolysis product of DMDMH, exposed to microorganisms derived from the activated sludge of a municipal sewage treatment plant was investigated under aerobic static exposure conditions.  The biodegradability, based on DOC removal, of DMH was determined to be 87% after an incubation time of 42 days. DMH at 20 mg/L achieved an average percent removal of 101.3% following a 16 day acclimation period and therefore may be classified as ultimately biodegradable provided a sufficient acclimation period occurs.

 

There are reliable biodegradation in water studies for DMDMH, but there is a reliable water degradation study available for the hydrolysis product, DMH.  A reliable study (Mead 2001) determined that DMDMH was degraded 78% within the 10-day window and the test substance can be considered readily biodegradable. Additional studies with the degradation product showed that DMH is also readily biodegradable. Consequently, the test substance and its hydrolysis product are considered readily biodegradable in the aquatic environment.