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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

No tests are required due to ready biodegradability of category members Fatty Acids.

Key value for chemical safety assessment

Additional information

The category members Fatty Acids are readily biodegradable. In accordance with column 2 of EC 1907/2006 Annex IX water and sediment simulation testing is not required for readily biodegradable substances.

For the sake of completeness available experimental results on simulation tests to assess the biodegradability of chemicals discharged in wastewater are summarized for the category member stearic acid (CAS No. 57-11-4).

Numerous experimental results for determining the extent and kinetics of primary and ultimate biodegradation by activated sludge are available for stearic acid since the substance is used as positive reference substance in a test design similar to OECD Guideline 314 B.
Biodegradation of radiolabeled stearic acid in the mixed liquor (water-soluble fraction and sorbed fraction; approximately 2500 mg/L suspended solids) during activated sewage treatment was determined. A known amount of stearic acid (1.0 or 0.1 mg/L) was added to the biotic sludge systems (abiotic systems were not tested in deviation to the guideline) and monitored for 28 days up to 140 days. The conversion of radiolabeled test substance to radiolabeled CO2 was measured by trapping evolved CO2 in base traps and by quantifying dissolved CO2 by LSC. The resulting data was used to develop the elimination rate of stearic acid and the extent of overall mineralization.

The overwhelming part of the reported data from these biodegradability tests of stearic acid prove this substances to be very well accessible to ultimate biodegradation under aerobic conditions resulting in cumulative degradation rates of 90%. The reported kinetic for stearic acid was highly variable (0.18 - 0.86 days-1) depending on the test substance concentration and test duration. The highest rates were achieved for test concentrations of 0.1 mg/L stearic acid. The plateau phase for degradation was reached for stearic acid as positive reference substance during the first weeks.