Photodegradation of the surfactants Na-dodecylbenzenesulfonate and dodecylpyridinium-chloride as affected by humic substances

Surfactants account for a great proportion of organic xenobiotica released into the environment by anthropogenic action. In natural waters and sewage sludge they can be removed from solution by different reactions, including adsorption to solid phases, biodegradation and abiotic photolytic degradation. In the present investigation we found that photodegradation of Na- dodecylbenzenesulfonate (LAS) was reduced by humic substances by a factor of 2 or more. In contrast, photodegradation of dodecylpyridinium-chloride (LPC) was increased in the presence of humic substances by a factor of 1.16-1.43. These differences were explained by the strong bonding of LPC but not of LAS to the humics. Photolytic degradation of LAS begins at the aliphatic side chains followed by aromatic ring cleavage. Photodegradation of LPC mainly associated with the humics showed similarity to that of pyridine. The experimental data demonstrate strong effects of photodegradation on the persistence of surfactants and the relevance of humic-surfactants associations for photolytic processes.[PUBLICATION ABSTRACT]