EFFECTS OF A NONIONIC SURFACTANT (C(14-15)AE-7) ON AQUATIC INVERTEBRATES IN OUTDOOR STREAM MESOCOSMS

Responses of aquatic invertebrates to a C-14-15 linear alcohol ethoxyl ate (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 inve rtebrates to 28- and 30-d exposures in eight stream mesocosms, Changes in benthic invertebrate densities and in invertebrate drift were moni tored during pretreatment, treatment, and posttreatment periods. In Ex periment 1, mean measured concentrations of surfactant were 0.08, 0.16 , and 0.33 mg LAE/L. In Experiment 2, mean measured concentrations wer e 0.11, 0.28, and 0.55 mg LAE/L. In each experiment, there were two tr eated streams at each surfactant concentration and two untreated strea ms that served as controls. No significant effects (p > 0.05) on popul ation densities of Copepoda, Cladocera, Chironomidae, Nematoda, or Ann elida were observed in either experiment. Moreover, no effects were de tected on the numbers of any of these organisms collected in drift net s. However, there was a significant decrease (p less than or equal to 0.05) in the densities of Simuliidae at surfactant concentrations grea ter than or equal to 0.16 mg LAE/L. This was accompanied by an increas e in the numbers of Simuliidae collected in drift nets; Based on these results, the no-observed-effect concentration for aquatic invertebrat es was 0.08 mg LAE/L, and the lowest-observed-effect concentration was 0.16 mg LAE/L.