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Environmental fate & pathways

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Di(2 -hydroxypropyl) tallowamine has a calculated pKa of 5.7 which means that the nitrogen is for the main fraction unprotonated under environmental conditions. Due to the long alkyl chain it will sorb mainly to the organic matter fraction in sludge, soil and sediment constituents.There is a strong similarity in molecular structure between di (2 -hydroxypropyl) tallow amine and di (hydroxyethyl) alkyl amines because they both contain a common alkyl chain length and a similar functional group. Certain missing fate data for di (2 -hydroxypropyl) tallow amine like the sorption/desorption data or fate in a sewage treatment plant are therefore read-across from di(2 -hydroxyethyl)oleyl amine or tri (2 -hydroxyethyl)hydrogenated tallow diamine. Justification for this analogue approach is presented in a separate document which is attached to paragraph 13.

For di(hydroxyethyl) oleyl amine the sorption to soil was measured using three different soils. The soil/water distribution coefficients (Kd values) observed range from: 2025 to 4639 L/kg. Biodegradation is considered to be the main removal mechanism of di (2 -hydroxypropyl) tallow amine since it is, like di (2 -hydroxypropyl) tallow amine or tri (2 -hydroxyethyl) hydrogenated tallow diamine readily biodegradable.

 

The half-life in the different environmental compartments will influenced by the bioavailability of the substances. No measured half-life data is available for di (2 -hydroxypropyl) tallow amine in soil or sediment. In absence of half-life data in these compartments these can as a worst-case be estimated based on the readily biodegradability and the sorption data as determined in a sorption desorption test.

As an alternative to determine the half-life in soil, also read-across from a similar substance may be applied. For 14C hexadecylamine a half-life in three soils was measured according to an OECD 307 test. Although this C16 amine is strongly sorbing to soil (median Kp soil of 3875 L/kg at lowest measured concentration), half-life’s of 8.14 to 8.98 days were observed at 20 °C. This value can be recalculated (EUSES) to 12 °C resulting in a maximum half-life in soil of 16.9 days. As both primary alkyl amines and primary alkyl amine propoxylates (2PO) are readily biodegradable, adsorb equally strong to soil and are structurally strongly related, it is considered acceptable to use a half-life of 17 days in soil and sediment for the primary fatty amine propoxylates risk assessment as well. Because of the absence of real measured sorption data for di (2 -hydroxypropyl)tallow amine an additional precautionary safety factor of 2 is applied on the half-life of 16.9 d. The Table below summarizes half-lives derived through default values and a simulation study.

 

Table Summary of degradation rate constants in various (eco) systems based the ready biodegradability of primary fatty amine propoxylates.

(Eco) system

Method

Half-life

Surface water (fresh)

TGD default value

15 days half-life

Surface water (fresh) sediment

TGD default value

33.8 days half-life

Marine water

TGD default value

50 days half-life

Soils

TGD default value

33.8 days half-lifea

Degradation in sewage treatment plants

Determined in bioreactors

>99.999% removal primarily by biodegradation

 aHalf-life of the fraction dissolved in the water phase is expected to be in the order of a few days.

 

Di (2 -hydroxypropyl)tallow amine has a short predicted half-life in air but because there are no important releases into the atmosphere and volatilisation is expected to be negligible, this removal mechanism is thought to be of low relevance. Di (2 -hydroxypropyl)tallow amine does not contain hydrolysable covalent bonds. Cleavage of a carbon-nitrogen bond under environmental conditions is only possible with a carbonyl group adjacent to the nitrogen atom. Degradation of di (2 -hydroxypropyl)tallow amine through hydrolysis is therefore not considered.

Direct photolysis of di (2 -hydroxypropyl)tallow amine in air/water/soil will not occur, because it does not absorb UV radiation above 290 nm. Photo transformation in air/water/soil is therefore assumed to be negligible.

No measured BCF fish is available for di (2 -hydroxypropyl)tallow amine. Standard OECD 305 tests are technically not feasible with these sorbing and easily degradable substances, since it will be impossible to reach steady state in such a test.

In addition, the route of exposure in a standard OECD 305 test is unrealistic for these substances because the substance will either be sorbed or biodegraded, The bioaccumulation potential of di (2 -hydroxypropyl)tallow amine was therefore assessed based on a measured log Kow. As indicated before, di (2 -hydroxypropyl)tallow amine is readily biodegradable and it is therefore unlikely that they will accumulate in the food chain. Since there is a measured log Kow value available this value can be used to evaluate the bioaccumulation potential.

 

primary fatty amines propoxylate

Measured Log Kow

(at pH 7)

Measured Log Kow

(at pH 3 - 4)

Calculated

Log Kow

(EPIsuite)*

Di (2-hydroxypropyl)hexadecylamine

5.7

3.3

3.93

Di (2-hydroxypropyl)octadecenylamine

6.1

3.6

4.7

Di (2-hydroxypropyl)octadecylamine

6.9

4.4

4.9

Di (2-hydroxypropyl)tallow amine

6.2

3.7

4.5

 *protonated

 

The log Kow observed for di(2-hydroxypropyl)tallow amine is 6.2 at pH 7 and 3.7 at a pH between 3 and 4.. For this product also a water solubility of 0.2 mg/L (at 20 °C and pH 9.3) was observed. The measured log Kow value of 6.2 at pH 7 indicates that this substance may have a bioaccumulation potential if it would have been a narcotic substance and if the metabolic rate of the substance is not taken into consideration. For polar narcotics like the primary fatty amine propoxylates however there is only limited information on the relationship between log Kow and BCF.

For hexadecyl amine rapid metabilisation in fish is anticipated based on in vitro metabolism test results with this substance (Kmet= 0.152 1/d; Bernard et al., 2006). Based on the structural similarity and ready biodegradability of the primary fatty amines similar metabolisation rates are expected for the primary fatty amine propoxylates. According to the REACH PBT guidance R.11, evidence of high biotransformation/metabolisation rate in fish may be used to support for arguing for a limited bioaccumulation potential but quantitative thresholds have not been established. The use of QSAR- and mechanistically-based bioaccumulation models is also considered valuable in the overall bioaccumulation assessment process. The BCFBAF model (v3.0) as included in EPIsuite (v4.0) allows the inclusion of metabolism into the BCF calculation but the results of this model should be considered with care as the training set holds only a limited number of substances which can reliably be used to predict the fate of cationic surfactants. With a log Kow of 6.2 the BCFBAF model predicts a BCF of 20880 L/kg without metabolism and 148.6 L/kg wwt with metabolism. The bioaccumulation potential of primary fatty amine propoxylates should based on this be considered as low.