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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The key study is a ready biodegradability test (OECD 301B) result, test performed according guidelines meeting validity criteria.  

Results from a non-glp semi continuous activated sludge test in combination  with closed bottle test results is used as supporting study.

Peer reviewed published articles are used as supporting studies

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

Ethanol, 2,2’-[[3-[2-hydroxyethyl]amino]propyl]iminobis-, N-alkyl derivatives are surfactants consisting of a hydrophilic part i.e. tri(hydroxyethyl)-1,3-diaminopropane linked to a hydrophobic alkyl moiety. Biodegradation of both moieties of surfactants usually requires the concerted action of at least two microorganisms as a single organism usually lacks the full complement of enzymatic capabilities (van Ginkel, 1996). The biodegradation mechanism of ethanol, 2,2’-[[3-[2-hydroxyethyl]amino]propyl]iminobis-, N-alkyl derivatives was deduced from semi-continuous activated sludge (SCAS) test results. In the SCAS test activated sludge was exposed to a specified concentration of 2,2’-[[3-[2-hydroxyethyl]amino]propyl]iminobis-, N-(coco alkyl) derivatives and the non-purgeable organic carbon (NPOC) was analysed frequently to determine the carbon removal (van Ginkel et al, 2009). This test has been performed according to OECD Test Guidelines (OECD, 1981). During the first two months (except day 3) the carbon removal ranged from 56 to 75% which suggests formation of hydrophilic compound(s). Thereafter the NPOC values of effluent of the unit fed with domestic wastewater spiked with ethanol, 2,2’-[[3-[2-hydroxyethyl]amino]propyl]iminobis-, N-(coco alkyl) derivativesdid decrease further. During the last weeks of the test the removal of ethanol, 2,2’-[[3-[2-hydroxyethyl]amino]propyl]iminobis-, N-(coco alkyl) derivatives increased to a level of >80% indicating degradation of the hydrophilic moeity.The most likely mechanism derived from SCAS test results is a C-N cleavage and a subsequent oxidation of the hydrophobic part (alkyl chain). This oxidation leads to formation of water-soluble tri(hydroxyethyl)-1,3-diaminopropane. Tri(hydroxyethyl)-1,3-diaminopropane represents approximately 40% of the carbon of the surfactant (Figure, see attached documents). The alkyl chain and the hydrophilic moiety are probably degraded by a consortium of microorganisms.

The initial partial carbon removal and the >80% carbon removal at the end of the test do rule out formation of persistent water-soluble substituted 1,3-diaminopropanes. At the end of the SCAS test the total organic nitrogen content was measured in the test and control unit to assess the removal of organic carbon. The removal of total organic nitrogen was 78% (80%, 75%). The high organic nitrogen removal percentages also prove that ethanol, 2,2’-[[3-[2-hydroxyethyl]amino]propyl]iminobis-, N-(coco alkyl) derivatives are ultimately biodegradable. A Closed Bottle test inoculated with adapted activated sludge from the SCAS test is suitable to predict ultimate biodegradation of ethanol, 2,2’-[[3-[2-hydroxyethyl]amino]propyl]iminobis-, N-(coco alkyl) derivatives, which is expected not to be in the aqueous phase because of their capacity to adsorb.In a Closed Bottle test with adapted sludge, ethanol, 2,2’-[[3-[2-hydroxyethyl]amino]propyl]iminobis-, N-(hydrogenated coco alkyl) derivativesamineis biodegraded 63% at day 28. The biodegradation percentage in excess of 60 indicates ultimate (complete) degradation. In ready biodegradability tests, the two moieties of this fatty amine derivative are degraded sequentially. The degradation curve will therefore be the sum of two growth curves. The biodegradation of the two moieties may be fully in line with the time-day window criterion when judged as separate chemicals. The time window criterion was developed on the assumption that a compound is degraded according to the “standard” growth curve in ready biodegradability tests. The time-window should therefore be ignored as a pass fail criterion for this surfactant in ready biodegradability tests. Ethanol, 2,2’-[[3-[2-hydroxyethyl]amino]propyl]iminobis-, N-(coco alkyl) derivativesis not readily biodegradable in a “standard” Closed Bottle test. The biodegradation is probably jeopardized by the toxicity of the test substance in the test. Inhibition of biodegradation by the test substance can in some cases be prevented through the addition of humic acid, lignosulphonic acid or silica gel, all known for their capacity to reduce the toxicity of cationic surfactants (van Ginkel et al, 2008). A ready biodegradability result was obtained with ethanol, 2,2’-[[3 -[2 -hydroxyethyl]amino]propyl]iminobis-, N-(coco alkyl) derivatives was obtained with humic acid.The biodegradation percentages were 63 and 75% at day 28 and 42, respectively. A carbon dioxide evolution test (Sturm test) incompliance with the OECD principles of Good Laboratory Practice was carried out with ethanol, 2,2’-[[3 -[2 -hydroxyethyl]amino]propyl]-iminobis-, N-(hydrogenated tallow alkyl) derivatives (Mead, 1997). This substance was biodegraded 61% at day 28. The time-window was ignored as a pass fail criterion because of the biodegradation kinetics. Hence 2,2’-[[3-[2-hydroxyethyl]amino]propyl]iminobis-, N-alkyl derivatives with alkyl chain lengths ranging from 12 to 18 carbons should be classified as readily biodegradable.