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Environmental fate & pathways

Biodegradation in soil

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Description of key information

Based on the available study on biodegradation, di (2-hydroxylpropyl) tallow amine is classified as readily biodegradable. The 10-days-window criterion should not be evaluated for a UVCB thus there is no requirement for performing a soil biodegradation test (Annex IX. 9.2.1.3). No simulation tests for degradation rates under environmental conditions are available for di (2-hdyroxypropyl) tallow amine but for a structurally very similar substance (hexadecyl amine). The results observed for the degradation in soil for this substance can be used for read-across to di (2-hydroxypropyl) tallow amine as both are readily biodegradable and have comparable sorption behavior in soil. Because of the absence of sorption data for di (2 -hydroxypropyl)tallow amine despite the fact that an identical sorption is expected a safety factor of 2 is applied to the half-life of 16.9 d at 12°C as observed for hexadecylamine resulting in a worst-case half-life for di (2 -hydroxypropyl)tallow amine in soil and sediment of 33.8 d.

Key value for chemical safety assessment

Half-life in soil:
33.8 d
at the temperature of:
12 °C

Additional information

Based on the available studies on biodegradation, the substances are estimated to be readily biodegradable, fulfilling the 10-days-window criterion thus there is no requirement for performing a soil biodegradation test (Annex IX. 9.2.1.3).

 

Default half-life’s

For the derivation of the default half-life’s the bioavailability is taken into account via the sorption properties of the substance. This is realistic for soluble non-toxic substances. For poorly soluble/strongly sorbing substances however, the degradation rate in a standard ready test is limited by the dissolution rate and in many cases not 60% degradation is achieved within 28 days but in a slightly longer time frame. Such a substance is in fact completely degraded to CO2and H2O and thus completely biodegradable. The bioavailable fraction is readily biodegradable but the due to the stringency of the test setup this cannot be observed.

No measured sorption data is available for di (2-hydroxypropyl)tallow amine. To fill the datagap the sorption data as observed for di (2-hydroxyethyl)oleyl amine is used. A justification for this read across is included in IUCLID chapter 13. For di (2-hydroxyethyl) oleyl amine a refined sorption/desorption test according to OECD 106 was performed and this test resulted in equilibrium constants (Kd's) of 2025, 4526 and 4639 L/kg for loamy sand, silt and clay soil. As there is no direct relationship with the sorption behaviour of the substance and the organic carbon content of the soil no soil Koc's are given. Due to this absence there is no principal difference between soil and sediments in respect to the sorption properties (EU-RAR primary alkyl amines) and the same Kd's are therefore considered to be applicable to soil and sediment.A mean Kpsoil for di (2-hydroxyethyl)oleyl amine can be calculated of 3730 L/kg (stdv: 1478 L/kg). The suggested maximum half-life for a readily degradable substance with a Kpsoil in the range >1000 and < 10000 L/kg is 3000 days for soil (at 12 ºC). These values are considered as extremely conservative but in the absence of measured data can be used in the exposure assessment as a worst-case. The half-life of the bioavailable fraction of primary fatty amine ethoxylates in the water phase of soils is expected to be in the order of a few days, which is based on experiments with dialkyldimethylammonium salts (van Ginkel et al, 2003).

Read across half-life in soil from primary alkyl amines

For hexadecylamine[1-14C] a substance which is structurally strongly related to di (2 -hydroxypropyl) tallow amine, there is an OECD 307 aerobic soil transformation study available and the results of this study can be used for read across to di (2 -hydroxypropyl) tallow amine. Both substances are readily biodegradable and no significant difference in sorption to soil is expected as the mean Kpsoil for di(2 -hydroxyethyl)oleyl amine is 3730 L/kg with a stdv of 1478 L/kg and for octadecyl amine a median Kp soil of 3875 L/kg was calculated from a OECD 106 sorption/desorption test.

Although half-life's of 3000 days at 12 °C are predicted for soil based on the readily biodegradability and the sorption data, very low measured half-life’s at 20 °C were determined for hexadecyl amine in three different soils: Soil 1 t1/2 = 9.0 d; Soil 2 t1/2 = 8.1 d; Soil 3 t1/2 = 8.9 d.

The median measured half-life of 8.9 d at 20 °C corresponds to a median half-life of 16.9 d at an environmental temperature of 12 °C (Q-10 rule REACH Guidance). This study demonstrates that 1-Hexadecanamine (C16 amine) is rapidly degraded in various soils and that the assumption of low degradation rates for strongly sorbing substances is not justified.

Because of the absence of sorption data for di (2 -hydroxypropyl)tallow amine despite the fact that an identical sorption is expected a safety factor of 2 is applied to the half-life of 16.9 d at 12°C as observed for hexadecylamine resulting in a worst-case half-life for di (2 -hydroxypropyl)tallow amine in soil and sediment of 33.8 d.