Glycerides, C16-18

Biodegradation in water: screening tests

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater

Additional information

A study was conducted to assess the biodegradability of low erucic acid rapeseed oil according to the Coordinating European Council Method CEC L-33 -T-82 (now called CEC L-33 -A-934). The method measured disappearance of CH3 -CH2 units by spectrophotometry. The test substance proved to degrade by more than 87.5% within 7 days and more than 91.8% within 21 days. Low erucic acid rapeseed oil can therefore be considered to fulfill the criteria for ready biodegradability under the conditions of the study (Fabig, 1989).

A study was conducted to determine the ready biodegradability of fully hydrogenated coconut oil according to OECD guideline 301F and EU method C4 -D.

Fully hydrogenated coconut oil was exposed to aerobic activated sludge from the aeration tank of a domestic waste water treatment plant for 28 days. The biodegradation was followed by the oxygen uptake of the micro organisms during exposure. As a reference item sodium benzoate was tested simultaneously under the same conditions as the test item, and functioned as a procedure control. Considering that fully hydrogenated coconut oil contains little amount of nitrogen, the nitrate concentration was measured. However, the nitrate concentration in the test item treated vessels was below LOQ. Therefore, no nitrification occurred. The reference item was degraded to more than 60% after 3 d of incubation. Under the test conditions, fully hydrogenated coconut oil was determined to be readily biodegradable, but failed the 10-d window (Feil, 2010).

A ready biodegradability study was conduced for castor oil according to "European Economic Communities, 1984. Method for the determination of ecotoxicity at level 1, Biodegradation, Repetitive Die Away Test. DG XI/400/84. Rev.1". A defined medium was inoculated with activated sludge, preconditioned during a week to reduce high residual respiration rates. The density of the inoculum was 35 mg s.s./l. The initial test material concentration was 7.5 g/L. The chemical oxygen demand (COD) was determined according to the method of Kelkenberg (1975). The toxicity control was a combination of test material with sodium acetate. The study was carried out in triplicate. The oxidation percentage was 50% after one week, increasing to 62% during the second week. Repetitive additions confirmed that the biodegradation level varied between 30% and 50% per week. Under the test conditions, the test material was found to be readily biodegradable (Balk and Meuwsen, 1988).