Amines, C16-18 and C18-unsatd. alkyl, ethoxylated

Biodegradation in soil

Description of key information

Based on the available studies on biodegradation, the substances are estimated to be 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 primary fatty amine ethoxylates but for a very similar substance (hexadecyl amine) and these results will be used for read-across to primary fatty amine ethoxylates (2EO). For soil and aerobic sediment this is a half-life value of 17 days at 12 °C.

Key value for chemical safety assessment

Half-life in soil:

17 d

at the temperature of:

12 °C

Additional information

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 the substance this cannot be observed.

The Kpsoil was determined as 4526 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 from primary alkyl amines

For hexadecylamine[1-14C] a substance which isvery similar to 2,2'-(C12-18 evennumbered alkyl imino) diethanol (CAS no 71786-60-2) there is an OECD 307 aerobic soil transformation study available and the results of this study will be used for read across to the primary alkyl amine ethoxylates for both the soil and sediment compartment. Although this C16 amine is strongly sorbing to soil (median Kp soil of 3875 L/kg at lowest measured concentration) the following half-life’s at 20 °C were determined for three soils: Soil 1 t1/2 = 9.0 d; Soil 2 t1/2 = 8.1 d; Soil 3 t1/2 = 8.9 d.

The median 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 (see 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 could be unjustified.