Responses of periphyton and invertebrates to a tetradecyl-pentadecyl sulfate mixture in stream mesocosms.

Alkyl sulfates (AS) are anionic surfactants widely used in household and personal cleansing applications. Aquatic toxicity of AS under laboratory conditions indicated effects at relatively low concentrations (50-230 microg/L) for some sensitive species. A comprehensive stream mesocosm study of an AS mixture composed of tetra- (C14) and pentadecyl (C15) chain lengths was conducted to better understand effects on microbial and macroinvertebrate populations and communities. A 56-d exposure of AS was performed at concentrations ranging from 57 to 419 microg/L (analytically confirmed exposures) and was accompanied by detailed investigations of periphyton community function (autotrophy, heterotrophy, and metabolism of test chemical), periphyton structure (algal population and community dynamics based on taxonomic identity), and invertebrate structure (benthic abundance, drift, and insect emergence patterns based on taxonomic identity). A no-observed-effect-concentration (NOEC) of 222 microg/L was concluded for several individual algal and invertebrate species based on univariate statistical analyses. An apparent energetic subsidy from C14-15AS at the highest concentrations of 222 to 419 microg/L was observed and tied to changes in microbial community processing of AS when added at these high concentrations. A multivariate analysis based on principal response curves (PRC) indicated that communities in streams exposed to 222 to 419 microg/L were significantly different from the controls leading to an overall (multivariate and univariate) conclusion that 106 microg/L was the ecosystem NOEC. Exposure to AS in the environment has been demonstrated to be in the range of 5 to 21 microg/L in 100% wastewater treatment plant effluent. Potential environmental effects are at least 5 to 20 times above worst-case environmental exposures; therefore, C14-15AS does not pose a risk to the aquatic environment due to normal use patterns.