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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The registered substance is a UVCB. A biodegradation study on the substance itself has been used to assess the biodegradation properties of the substance for the purpose of classification and labelling. The data indicates that the substance and its underlying constituents are readily biodegradable. In order to assign a biodegradation rate to the two assessment entities being used for the environmental exposure and risk assessment, available experimental data on Hydroxycitronellal and Methyl Anthranilate (methyl 2-aminobenzoate) has been used. Both of these individual substances are readily biodegradable. Therefore the key value of "readily biodegradable" has been assigned to all assessment entities. For the PBT assessment, data on the whole substance and the assessment entities has been considered.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

One biodegradation study is available for the registered substance, Aurantiol Pure. The ready biodegradability has been investigated using a standard ready screening method, the OECD 301F Manometric Respirometry Test (Key study, Rudio 1999). The percentage of biodegradation achieved after 28 days was 70%. Biodegradation starts on day 3 and reaches 63% at the end of the 10 day window (days 3 to 13). Thus Aurantiol Pure was regarded as readily biodegradable according to this test.  

Aurantiol Pure is a UVCB. It is recognised that standard biodegradation tests are not ideally suited to mixtures because they measure ultimate biodegradation as a function of either the CO2 evolved or O2 consumed and as such do not provide information on the biodegradability of individual constituents. However, the registered substance is a mixture of reaction products which are unstable in solution, being on purpose, precursors for Methyl Anthranilate and Hydroxycitronellal. Thus for the purposes of the PBT assessment and in order to assign a biodegradation rate to the two assessment entities for environmental risk assessment, available information on these two individual substances has been used. The ready biodegradability of Methyl Anthranilate (Rudio 1996) and Hydroxycitronellal (King 1994) were determined in separate standard biodegradation screening tests (OECD301F and sealed CO2 test respectively). The levels of biodegradation achieved after 28 days were respectively 85% and 94%. The 10 day window was met in both cases. Thus Methyl Anthranilate and Hydroxycitronellal are regarded as readily biodegradable according to these tests.

In the neat state, the registered substance contains some Methyl Anthranilate and Hydroxycitronellal as remaining starting materials (approximate total weight 29%). The fact that the degradation levels observed in the test performed on Aurantiol Pure were significantly higher than 29%, indicate that the condensation products in Aurantiol Pure are either rapidly hydrolysed to Methyl Anthranilate and Hydroxycitronellal and/or rapidly biodegraded themselves. Thus Aurantiol Pure and its underlying constituents are regarding as rapidly biodegradable for the purposes of classification and labelling and PBT assessment.

An inhibition control was included in the 301F ready biodegradability test performed on Hydroxycitronellal (Rudio, 1996). At the concentration used in the test (100mg/l), Hydroxycitronellal was not inhibitory to the microorganisms. Methyl anthranilate was shown to be readily biodegradable in a test performed at 10mg/L (King, 1994). These concentrations can be considered as NOECs for the toxicity to STP microorganisms for the two respective assessment entities (see endpoint on toxicity to microorganisms for further details).