Effects of internal hydrophilic groups of a newly developed sustainable anionic surfactant on biodegradability and ecotoxicity

Recently, a new sustainable anionic surfactant called bio-based internal olefin sulfonate (Bio IOS) has been developed. This surfactant enables excellent water solubility and high surface activity. It has a unique structure of long hydrophobic alkyl chains (C16 to C18) with two types of hydrophilic groups in its midsection, which distinguish it from other conventional anionic surfactants. However, the effects of the specific structural features of the surfactant on its environmental properties and the consequent effects on the environment remain unclear. In this study, we investigated the environmental fate and ecotoxicity of Bio IOS and the effects of the types and positions of hydrophilic groups on biodegradability and ecotoxicity. Biodegradation studies demonstrated that Bio IOS was readily biodegradable with >99.5% removal in wastewater treatment activated sludge (test concentration: 1 mg/L) and a fast half-life of 5.8 h in river water (test concentration: 10 μg/L); the excellent biodegradability was likely due to the high water solubility attributed to the internal hydrophilic groups. Meanwhile, moderately toxic effects were observed, whereby the 50% lethal and effect concentrations of the three freshwater species were above 1 mg/L. Ecotoxicity studies with different types and positions of hydrophilic groups revealed that hydroxyalkane sulfonate was less toxic and that toxicity was reduced in the presence of more internally located hydrophilic groups. These findings suggest that the hydroxyl group and the internal positions of hydrophilic groups that constitute the molecular configuration resembling two separate shorter alkyl chains may reduce the adverse effects on organisms despite the long alkyl chains.