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

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 (C12AES), sodium dodecyl sulfate (SDS), dodecyl alcohol ethoxylate (C12AEO) and dodecyl benzenesulfonate (C12LAS). A brief acclimatization period has been required to enable an effective degradation of C12LAS and C12AES to take place, but this lag phase has not been detected for SDS and C12AEO. 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 C12LAS was also monitored. C12LAS external isomers, which are predominant, are preferentially degraded by successive β-oxidations, generating significant amounts of external even isomers of sulfophenylcarboxylic acid (SPC) (mainly 2,3ΦC4,6SPCs). In ontrast, internal isomers are converted into internal odd isomers of SPC (mostly 4,5ΦC5,7SPCs) by ω-oxidation followed by α-oxidation and/or β-oxidations.