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Environmental fate & pathways

Biodegradation in water: screening tests

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N-[3-(tridecyloxy)propyl]-1,3-propane diamine, branchedmonoacetate and N-[3-(tridecyloxy)propyl]-1,3-propane diamine branched is an etheramine surfactant characterized by a hydrophobic moiety i.e. tridecyl and a structurally related hydrophilic moiety of dipropylenetriamine linked together with an ether bond. Biodegradation of surfactants refers to the reduction in complexity of the chemical through metabolic activity of microorganisms. If a surfactant is to serve as a carbon and energy source for aerobic microorganisms then it has to be converted into a form that can enter the central metabolism of microorganisms. Normally this involves converting the surfactant into one, or more, low molecular weight intermediates of the tricarboxylic acid (TCA) cycle or compounds that feed into it. Many of these conversions are described in pathways forsurfactants (van Ginkel, 2007). Although micro-organisms capable of degrading surfactants are immensely diverse, the central metabolism (b-oxidation and TCA cycle) is remarkably similar. Kluyver and Donker (1920) first described this similarity known as the unity of biochemistry. This unity is the key to justification of the use of read-across.

Based on the structure of 1,3-propanediamine, N[3-(tridecyloxy)propyl]-, branched the following biodegradation pathways is most plausible: an attack on the hydrophilic part of the molecule followed by the degradation of the alkyl chain. A structurally related compound of the hydrophilic moiety dipropylene triamineis metabolised through ß-alanine, which feeds into the TCA cycle. Dipropylene triamine(N-(3-aminopropyl)-1,3-propanediamine) is readily biodegradable (van Ginkel et al, 2009; Rothkopf and Bartha, 1984). The biodegradability of the hydrophilic moiety is expected to be comparable with dipropylentriamine. The biodegradability of the branched alkyl chains are expected to be NOT readily biodegradable because of branching. Branched alcohols are known to be inherently biodegradable.

N-[3-(tridecyloxy)propyl]-1,3-propane diamine, branched monoacetate and N-[3-(tridecyloxy)propyl]-1,3-propane diaminebranchedis therefore expected to be not readily biodegradable. Indeed,N-[3-(tridecyloxy)propyl]-1,3-propane diamine, branched monoacetate and N-[3-(tridecyloxy)propyl]-1,3-propane diamine branchedwas biodegraded 8% at day 28 in the Closed Bottle test. In the prolonged Closed Bottle test (enhanced biodegradability testing) a biodegradation percentage of 63 was achieved at day 60 (AkzoNobel, 2010). This result could only be achieved by using a high concentration of humic acid (van Ginkel et al, 2010).N-[3-(tridecyloxy)propyl]-1,3-propane diamine,branched monoacetate and N-[3-(tridecyloxy)propyl]-1,3-propane diamine branched should be classified as NOT persistent because of the prolonged Closed Bottle test (enhanced test) result and the biodegradability of structurally related substances