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Environmental fate & pathways

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In an experiment in accordance with OECD Guideline 301 F and EU Method C.4-D tributyl citrate was investigated for its biodegradability potential (Feil, 2010). Aerobic activated sludge, collected from a domestic sewage treatment plant, served as inoculum. Sodium benzoate (purity of 100 %) was used as reference compound. Also a toxicity control (test item and reference compound mixed) was run in parallel, to ensure, that the chosen test concentration was not inhibitory to microorganisms. The degradation rate of the test item was calculated by the oxygen consumption of the aerobic activated sludge microorganisms after 28 days of incubation. The mean biodegradation after 28 days of the test substance was 74 %; the 10 day window criterion was not passed and therefore it is considered to be readily biodegradable, but failing the 10-day window. The reference item sodium benzoate attained 88 % degradation after 28 days, confirming the suitability of the aerobic activated sludge inoculum used. The test item had no inhibitory effect the aerobic activated sludge microorganisms and all validity criteria of the test method were met.

Biodegradation in water and sediment

Based on the available data tributyl citrate is considered to be rapidly biodegradable. Simulation testing on ultimate degradation in surface water, information requirement 9.2.1.2 in Annex IX, does not need to be conducted, as tributyl citrate (TBC) is considered to be rapidly biodegradable. The mean biodegradation after 28 days of the test substance was 74 %, the 10 day window criterion was not passed [OECD Guideline 301 F, 2010].

Simulation testing on ultimate degradation in sediment, information requirement 9.2.1.4 in Annex IX, does also not need to be conducted, as it has been shown in soil biodegradation tests with the structural analogue acetyl tributyl citrate (CAS 77-90-7; ATBC) that the test substance is readily biodegradable.

The hazard assessment of TBC reveals neither a need to classify the substance as dangerous to the environment, nor is it a PBT or vPvB substance, nor are there any further indications that the substance may be hazardous to the environment. Therefore, a simulation test on biodegradation in surface water and sediment is scientifically not justified.

Biodegradation in soil

No experimental data is available to assess the biodegradation in soil of tributyl citrate. From several test results on mineralisation in soil and compost, acetyl tributyl citrate can be classified as readily biodegradable in these substrates. The reduced degradation in one test with compost can probably be attributed to deficiencies in the applied method.

In a test on biodegradation in soil according to EPA OPPTS 835.3300 tributyl-O-acetylcitrate (CAS 77-90-7) was found to be readily biodegradable (Farrell, 2000). The same was concluded out of a Respirometry test in ‘static’ compost biometer system (Farrell, 2000). Microbial degradation of the test substance in the compost was, in part, retarded at the very high substrate loading used in another experiment (Farrell, 2000). Despite randomisation in bioreactor placement, the reduced air supply due to NaOH crystal formation in the air distribution manifold became more significant along the manifold and throughout the exposure period, potentially influencing the results achieved during this study. It can be assumed that the same applies to tributyl citrate (CAS 77-94-1) as it is a near analogue to the test substance acetyl tributyl citrate.