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Environmental fate & pathways

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Screening test for environmental fate and pathways were conducted for tributyl citrate. The biodegradation potential in water was investigated experimentally according to OECD Guideline 301F (Feil, 2010). The test substance was found to be readily biodegradable but failing the 10-d window. Regarding biodegradation in soil, experimental results are available of the read-across approach tributyl-O-acetylcitrate (CAS 77-90-7, please refer to the separate read-across statement for further explanation of this procedure). The substance can be considered to be readily biodegradable based on the results on mineralisation in soil and compost (both: Farrell, 2010). The reduced degradation in one test with compost can probably be attributed to deficiencies in the applied method (Farrell, 2010). 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.

In consequence, no simulation test for biodegradation in water and sediment has to be conducted (in accordance with REACH, Annex IX, Section 9.2.1.2, Column 2).

Tributyl citrate can be considered as hydrolytically stable, resulting from a prediction performed with HYDROWIN v2.00 (by US-EPA).

Also the Bioconcentration factor (BCF) was predicted with the help of the US-EPA computer program BCFBAF v3.01, resulting in an BCF of 94.7 L/kg wet wt, based on the traditional method and taken into account the experimentally determined LogPow of 3.5 (Frischmann, 2011). The Arnot-Gobas method resulted in a value of 6.54 L/kg wet wt.

Another QSAR prediction was performed for tributyl citrate regarding phototransformation in air, resulting in an overall gas-phase reaction constant of 16.04 E-12 cm³/molecules-sec (= 0.14 m³/molecules-day), with an half-life of 0.67 d (8.00 h) by assuming a 12 h day with an OH rate constant of 1.5E6 OH/cm³ and 25 °C, thus it can be concluded that the substance will be rapidly degraded in air.

The Henry's Law Constant was calculated with the US-EPA computer program HENRYWIN (v3.20) to be 3.55 E-004 Pa*m3*mol-1 at 25°C.

The computer program KOCWIN v2.00 (by US-EPA) was used to predict the organic-normalised sorption coefficient for soil (Koc), using two different models. The MCI method is taken more seriously into account, due to the fact that is includes improved correction factors, resulting in a Koc value of 769.9 L/kg for the chemical compound. The traditional method gives a value of 208.2 L/kg, concerning the experimentally determined LogPow of 3.5 (Frischmann, 2011).

Further, the adsorption potential to soil / sewage sludge of tributyl acetylcitrate was investigated in a study conducted according to OECD 121 and EU method C.19 using the HPLC method. A log Koc of 4.271 was determined. 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.

Due to the rapid biodegradation, no monitoring data or field study results are available for tributyl citrate. These types of experiments are also not mandatory under REACH.