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Biodegradation in water: screening tests

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Description of key information

The test substance n-DDSA (CAS No. 19780-11-1) achieved 60% CO2 evolution at day 28 of an OECD 301B assay, but failed to meet the 10-d window; therefore, the substance meets OECD’s definition of a test substance which has shown evidence of “inherent, ultimate biodegradability”.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable but failing 10-day window

Additional information

In the study entitled “n-DDSA – Determination of the Biodegradability of a Test Substance Based on OECD Method 301B (CO2 Evolution Test)” (McLaughlin Smithers Viscient, 2012) a mixture of activated sludge (domestic source), soil, river sediment and river water were used to determine biodegradability of the test substance based on CO2 evolution. The mean cumulative net percent CO2 evolved (percent biodegradation) from the aqueous test medium fortified with n-DDSA at 10 mg C/L was 61.56% on day 28. The toxicity control on day 3 was 29.42%, which indicates that the test substance was not toxic to the inoculum in the test medium.

 The cumulative net percent CO2 evolved from the sodium benzoate procedural control was 60.57% of theoretical by day 3, thus exceeding the “pass” criteria of the test (reaching 60% or greater CO2 evolution within a 10-day window of reaching 10% biodegradation). This rapid biodegradation of sodium benzoate confirmed the presence of an active microbial population and system integrity.

 Based on the CO2 analysis results from this study, n-DDSA cannot be characterized as ‘readily biodegradable’ according to the OECD 301B guideline (does not reach 60% or greater CO2 evolution within a 10-day window of exceeding 10% biodegradation).

However, this test substance meets OECD’s definition of a test substance which has shown evidence of “inherent, ultimate biodegradability”.