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Biodegradation in water: screening tests

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Description of key information

The test substance was "readily biodegradable" in an ISO Draft (BOD Test for Insoluble Substances). Diisotridecyl phthalate reached a degradation of 71% after 28 days. 

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

The test substance (CAS-Nr. 27253 -26 -5) reached a degradation of 71% after 28 days, but failing the 10 -day window in an ISO Draft (BOD Test for Insoluble Substances. However, for an UVCB the 10 -day window is not required to reach the status of "readily biodegradable". According to Guidance on the Application of the CLP Criteria Guidance to Regulation (EC) No 1272/2008 on classification, labelling and packaging (CLP) of substances and mixtures Version 4.1 June 2015 Substances are considered rapidly degradable in the environment if one of the following criteria holds true: (a) if, in 28-day ready biodegradation studies, at least the following levels of degradation are achieved: (i) tests based on dissolved organic carbon: 70 %; (ii) tests based on oxygen depletion or carbon dioxide generation: 60 % of theoretical maximum. These levels of biodegradation must be achieved within 10 days of the start of degradation which point is taken as the time when 10 % of the substance has been degraded; unless the substance is identified as an UVCB or as a complex, multi-constituent substance with structurally similar constituents. In this case, and where there is sufficient justification, the 10-day window condition may be waived and the pass level applied at 28 days. ”Also according to Revised Introduction to the OECD Guidelines for Testing of Chemicals, Section 3 "Although these tests are intended for pure chemicals, it is sometimes relevant to examine the ready biodegradability of mixtures of structurally similar chemicals like oils and surface-active substances (surfactants). Such substances often occur as mixtures of constituents with different chain-lengths, degree and/or site of branching or stereo-isomers, even in their most purified commercial forms." The reference substance diethylene glycol achieved a degree of degradation of 78% after 14 days, thus confirming suitability of inoculum and test conditions.

In other studies the similar substance (with the CAS-Nr 68515 -47-9) was inherently biodegradable and has been shown to biodegrade to a high extent in an extended ready biodegradation test using a standard OECD test guideline. It has also demonstrated a moderate extent of biodegradability in a simulation test using river water, and moderate degree of removal in a wastewater treatability test. DTDP exhibited 63% biodegradation after 56 days, in an extended ready biodegradability test. Biodegradation data for a mono ester that is a mixture containing approximately equal amounts of monoesters with normal octyl (n-C8) and normal decyl (n-C10) side chains are available to assess the potential biodegradability of the primary transformation product.  Results show that this mixture is readily biodegradable (Scholz, 2003). MTDP is expected to exhibit an equally high extent and rapid rate of biodegradation as was demonstrated by MC8/10PE.