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Environmental fate & pathways

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Environmental fate data of various alkyl-1,3 -diaminopropanes has been used for the evaluation of the environmental fate of this category. The justification for the read-across is based on the similarities in their chemical structure, physico-chemical and environmental fate properties. All alkyl-1,3-diaminopropanes under consideration consist of carbon, hydrogen and nitrogen only. The basic structure includes a hydrocarbon chain with a 1,3-propanediamine group at the end of the chain. Due to the identical position of the functional diamine group and the identical CH2-groups adjacent to the diamine group, no difference in chemical reactivity is expected for the functional group. The only difference consists of differing chain lengths and slight variations in the degree of saturation in the alkyl chain. Since the majority of the alkyl chains consist of C12 to C18-units, and the unsaturated part is mainly located in the more central part of the alkyl chain, significant changes in chemical behavior and/or reactivity is not to be expected.

Alkyl-1,3 -diaminopropanes are protonated under ambient conditions. This means that they will sorb strongly to negatively charged surfaces like glassware, soil and sediment constituents. For four different soils Kd-values were observed ranging from 250 to 850 L/kg for N-C16 -18-alkyl (even-numbered) propane-1,3-diamine (CAS no. 133779-11-0). Biodegradation is considered to be the main removal mechanism of this substance. The half-life in the different environmental compartments is expected to be short. No measured data is available which quantifies the half-life of diamines in soil or sediment. These values can therefore be estimated as a worst-case based on the readily biodegradability and the sorption data as determined in the sorption desorption test. For14C-labelled hexadecylamine, a substance structurally strongly related to the alkyl-1,3 -diaminopropanes, a half-life in three soils was measured according to an OECD 307 test. Half-lives of 8.1 to 9.0 days were observed at 20 °C or recalculated to 12 °C (EUSES) a maximum half-life in soil of 17 days. For octadecylamine a similar sorption was observed as for octadecyl-1,3-diaminopropane. As both primary alkyl amines and alkyl-1,3 -diaminopropanes (diamines) are readily biodegradable and have a comparable sorption to soil and sediment, it is considered reasonable to use an half-life of 17 days in soil and sediment for the N-C12-14 alkyl-1,3 -diaminopropane risk assessment as well.

The observed removal in a waste water treatment simulation test was 99.4% for N-C16-18-alkyl (even-numbered) propane-1,3-diamine (CAS no. 133779-11-0) using specific chemical analyses (LC-MS/MS) during day 56 to 60 (n=5). In addition the sorption to sludge was measured and this accounted for 4.1% of the total removal which means that 95.3% was removed by biodegradation.

Environmental degradation rates for the exposure assessment

 

DT50(days)

Degradation in water

15

Degradation in seawater

50

Degradation in sediment

17

Degradation in soil

17

 

Diamines have 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. Diamines do 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 diamines through hydrolysis is therefore not considered.

Direct photolysis of diamines 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.

Standard OECD 305 tests to assess the bioaccumulation are technically not feasible with these strongly sorbing easily degradable substances. Several attempts have been made which demonstrated that maintaining a steady state exposure at the low aquatic concentrations required is impossible. Furthermore, 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 diamines was therefore assessed based on a measured log Kow. These log Kow values were measured using the slow stirring method according to OECD 123. This test was performed for amines, N-9 -octa-decenyl-, (Z)-propane-1,3 -diamine (7173 -62 -8), N-hydrogenated C16 -18 -alkyl-(evennumbered)propane-1,3 -diamine (68603 -64 -5) and N-Alkyl (C12 -C14) -1,3 -diaminopropane (90640 -43 -0) and resulted in log Kow values of respectively 0.0, 1.5 and -0.6 indicating a low bioaccumulation potential. The calculated log BCF using EPIsuite (v4.0) are respectively 0.66, 0.5 and 0.5.

Like for the primary alkyl amine and ethoxylated(2EO)alkyl amines biotransformation has been observed for C12 and C14 alkyldiamines in an in-vitro biotransformation test using hepatic S9 subcellular fraction indicating that bioaccumulation of diamines in fish is very unlikely.