Effects of a nonionic surfactant (C14-15AE-7) on aquatic invertebrates in outdoor stream mesocosms

Abstract

Responses of aquatic invertebrates to a C14–15 linear alcohol ethoxylate (LAE) nonionic surfactant with an average of seven ethylene oxide units per mole of alcohol were evaluated in outdoor stream mesocosms. Two experiments were carried out to evaluate responses of aquatic invertebrates to 28- and 30-d exposures in eight stream mesocosms. Changes in benthic invertebrate densities and in invertebrate drift were monitored during pretreatment, treatment, and posttreatment periods. In Experiment 1, mean measured concentrations of surfactant were 0.08, 0.16, and 0.33 mg LAE/L. In Experiment 2, mean measured concentrations were 0.11, 0.28, and 0.55 mg LAE/L. In each experiment, there were two treated streams at each surfactant concentration and two untreated streams that served as controls. No significant effects (p > 0.05) on population densities of Copepoda, Cladocera, Chironomidae, Nematoda, or Annelida were observed in either experiment. Moreover, no effects were detected on the numbers of any of these organisms collected in drift nets. However, there was a significant decrease (p ≤ 0.05) in the densities of Simuliidae at surfactant concentrations ≥0.16 mg LAE/L. This was accompanied by an increase in the numbers of Simuliidae collected in drift nets. Based on these results, the no-observed-effect concentration for aquatic invertebrates was 0.08 mg LAE/L, and the lowest-observed-effect concentration was 0.16 mg LAE/L.