Evaluating the sorption of organophosphate esters to different sourced humic acids and its effects on the toxicity to Daphnia magna

Abstract

Because of large usage as flame retardants and additives, organophosphate esters (OPEs) are widely detected in the environment and regarded as emerging contaminants. However, the sorption of OPEs to organic matter and its effects have scarcely been studied. In the present study, the sorption of 9 commonly used OPEs to 4 representative humic acids-Elliott Soil humic acid, Suwannee River humic acid, Aldrich humic acid, and Acros humic acid-in the range of 0mg/L to 50mg/L dissolved organic carbon (DOC), was evaluated with negligible-depletion solid-phase microextraction and verified by its impacts on the toxicity to the aquatic invertebrate Daphnia magna. Whereas OPEs with a high octanol/water partition coefficient (logKOW=4.51-6.64) were associated with humic acids mainly by hydrophobic interaction with DOC partition coefficient (KDOC) in the range of 102.22 to 105.31, the sorption of low-KOW OPEs (logKOW=-0.65 to 2.59) to humic acids was not hydrophobic interaction-dominant, with KDOC in the range of 103.47 to 104.29. These results were corroborated by the effects of humic acids on the acute toxicity of 3 high-KOW OPEs to D. magna. The sorption of OPEs to Suwannee River humic acid was weak and had negligible effects on the toxicity of high-KOW OPEs; the presence of terrestrial Acros humic acid (50mg/L DOC), however, significantly decreased the toxicity by 53% to 60%. The results indicated that the strong sorption between high-KOW OPEs and terrestrial humic acid might affect their transportation and bioavailability. © 2013 SETAC.