Influence of the hydrophilic moiety of anionic and nonionic surfactants on their aerobic biodegradation in seawater

Abstract

The extent and kinetics of the primary biodegradation have been characterized for the most commonly-used surfactants, employing four homologues with the same alkyl chain: dodecyl ethoxy sulfate (C(12)AES), sodium dodecyl sulfate (SDS), dodecyl alcohol ethoxylate (C(12)AEO) and dodecyl benzenesulfonate (C(12)LAS). A brief acclimatization period has been required to enable an effective degradation of C(12)LAS and C(12)AES to take place, but this lag phase has not been detected for SDS and C(12)AEO. Primary biodegradation percentages at the end of these experiments were higher than 99%, showing a fast degradation rate in all cases (average half-life lower than 2 days). The secondary biodegradation of C(12)LAS was also monitored. C(12)LAS external isomers, which are predominant, are preferentially degraded by successive beta-oxidations, generating significant amounts of external even isomers of sulfophenylcarboxylic acid (SPC) (mainly 2,3PhiC(4,6)SPCs). In ontrast, internal isomers are converted into internal odd isomers of SPC (mostly 4,5PhiC(5,7)SPCs) by omega-oxidation followed by alpha-oxidation and/or beta-oxidations.