Behavior of aliphatic alcohol polyethoxylates and their metabolites under standardized aerobic biodegradation conditions

Abstract

Aerobic biodegradation of aliphatic alcohol polyethoxylates (AEs) was tested under screening test conditions (Organization for Economic Cooperation and Development [OECD] 301E protocol) using recently developed analytic methodologies for the specific determination of AEs and their neutral (polyethylene glycols [PEGs]) and carboxylic (carboxylated PEGs and AEs) aerobic metabolites. Biodegradation screening tests were performed under the same conditions on three typical, commercial AE blends and an individual, linear AE ethoxymer. The linear and monobranched AEs underwent a fast primary biodegradation, whereas the multibranched AEs underwent a slower biodegradation. Based on the formation and oligomeric distribution of PEGs and the lack of detection of other biointermediates before the formation of PEGs, the central cleavage of the AE molecule appeared to be the mechanism for primary biodegradation of the linear and monobranched AEs in the tested commercial blends. As a result, the shorter AE ethoxymers biodegraded faster than the longer ones. No PEGs were detected during biodegradation of the multibranched AEs. In addition, PEGs biodegraded more slowly than the parent AEs and were removed by hydrolysis, thus leading to shorter PEG oligomers, and by oxidative hydrolysis, thus forming carboxylated PEGs.

Aerobic biodegradation of monobranched aliphatic alcohol polyethoxylates

“…The subsequent primary degradation was slower, however, and was completed 45 d later. Only PEGs were detected as biointermediates during biodegradation of the linear AE blend, and their recorded amount confirmed previous results [10]: A maximum value (73% on a molar basis of the initial AE concentration) was reached 4 d after the start, and their complete disappearance occurred during the following 7 d.…”

“…2 and 4). The second step occurs after preferential removal of the linear components of the blend, both as expected [10] and as confirmed by the biodegradation of 2Bu-C 8 AE in the presence of linear AE, in which 2Bu-C 8 AE started to be removed only when the linear AE disappeared (Fig. 3).…”

“…A preliminary analytic investigation on the aerobic biodegradation of the 2Bu-C 8 AE using high-performance liquid chromatography-mass spectrometry [13] allowed identification of mono-, di-, and tricarboxylated AE biointermediates in the test liquors. This is in contrast to the behavior of monobranched AE containing short alkyl chains [10].…”

“…Sample extraction and derivatization reactions were performed according to methods reported elsewhere [10].…”

“…In a recent study concerning aerobic biodegradation of commercial AE blends, the tested oxo-AE mixture, which contained AE isomers with short 2-alkyl chains such as 2-methyl-, 2ethyl-, and 2-propyl-substituted AE, degraded more slowly than the linear AE blend, and only metabolites of the polyethylene glycol (PEG) type were detected [10]. This finding indicated that the central cleavage mechanism, which was the only one that could account for the formation of PEG [8], was responsible for the biodegradation of both linear and monobranched AE isomers contained in the oxo-AE blend.…”