Effect of sediment organic carbon on the toxicity of a surfactant to Hyalella azteca

According to current sediment bioavailability models (e.g., equilibrium partitioning), toxicity of sorptive compounds in sediment depends on the free concentration in interstitial water. This free concentration may depend on both the characteristics of the compound and the sediment. For the sorption of anionic surfactants, sediment organic carbon content and cation exchange capacity have been shown to be important factors; however, it is not clear how these factors affect toxicity. Determining toxicity of these compounds in sediment using traditional batch sediment tests has not been entirely successful in the past due to excessive loss of parent material via biodegradation. In this study, effects of organic carbon on anionic surfactant toxicity were determined using highly branched alkylbenzene sulfonate (ABS)as the test compound in order to limit losses from biodegradation. Sediments were amended with pear moss to investigate the effects of organic carbon on surfactant sorption and toxicity to Hyalella azteca, Results support previous hypotheses regarding the effect of organic carbon on bioavailability and toxicity. Apparent sorption coefficients (K-app) increased with higher organic carbon levels. Likewise, greater sediment concentrations of ABS were required to elicit toxic responses at greater organic carbon concentrations. Toxicity in sediment appeared to be due to interstitial water exposure.