Dioctadecyl 3,3'-thiodipropionate

Biodegradation in water: screening tests

Description of key information

Readily biodegradable

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

The degradability of dioctadecyl 3,3'-thiodipropionate (DSTDP) was object of several studies:

A publication (Blok et al. 1985) about a harmonisation of biodegradability tests refers to 7 biodegradability tests results of the substance according to 4 different test methods used in OECD Round Robin Tests in1979 and 1980 (biodegradabilities: Sturm 0%, Closed bottle 0%,MITI II 60% , MITI I 40% ). No further details on test substance concentration, test design, inoculum and single results of the tests were given.

An OECD 301 B (modified Sturm test, 1989) resulted in a mineralization of 2 % in 28 days using a test concentration of 23.9 mg/L. Using a test concentration of 11.3 mg/L a mineralization of 15 % in 28 days was observed. Nonylphenol was used as emulsifier.

In an 14 d OECD 301C (MITI 1) test (JETOC 1992), using 100 mg/l test substance and 30 mg/l sludge concentration 51% degradation based on BOD and 74% degradation based on HPLC analysis was observed.

In a more recent study (2006) the degradability of dioctadecyl 3,3'-thiodipropionate (DSTDP) was investigated in a closed bottle test according to OECD 301 D with slight modifications using test concentrations of 2mg/l . Test substance dissolved in dichloromethane was added to 250-300 ml BOD bottles. Thereafter, the dichloromethane was evaporated during 24 hours on a roller bank before adding mineral medium and inoculum. The concentration of inoculum (secondary activated sludge derived from a municipal STP) was 2 mg dw/l. The test bottles were placed on magnetic stirrers for 28 days in the dark. The biodegradation of DSTDP was 71% in 28 days based on the BOD/ThOD-ratio. It reaches the pass level of 60% biodegradation for respirometric methods according to OECD 301 in 21 days. The criteria for the 10 -day window were not met.

Because of the poor solubility and high adsorption potential of the substance the modified OECD 301 D test result (71 % in 28 days) is considered to reflect more appropriately the biodegradation potential of the substance than the results of the OECD 301 B –test 1989 (2 % in 28 days and 15 % in 28 days) and the publication of 1985 as these tests were performed in exceedance of the water solubility and limited availabilty for biodegradation can be assumed.

Based on the modified OECD 301 D test result using lower concentrations of the substance, the substance is considered as readily biodegradable without meeting the 10-day window.

This conclusion is supported by a 14 d OECD 301C (MITI 1) test (JETOC 1992).

According to Regulation (EC) No 1272/2008 the pass level of degradation within 10 days of the start of degradation can be waived if the substance is an UVCB or a complex multiconstituent substance.

Additionally, according to Regulation (EC) No 1272/2008 substances can be considered as rapidly degradable if other convincing scientific evidence is available to demonstrate that the substance can be degraded (biotically and/or abiotically) in the aquatic environment to a level > 70 % within a 28-day period.

As there is evidence that the substance degrades within several hours (see IUCLID section 4.8) it can be concluded that the relevant degradation products are Octadecanol (CAS 112-92-5) and thiodipropionic acid (CAS 111-17-1). Both substances are readily biodegradable (ECHA disseminated data) and for CAS 693-36-7 a biodegradation of > 70% within a 28-day period was observed.

Based on these findings it can be concluded that the substance dioctyadecyl 3,3'-thiodipropionate can be considered as readily biodegradable.