Responses of aquatic invertebrates to a C9–11 non-ionic surfactant in outdoor stream mesocosms

Abstract Responses of aquatic invertebrates to a C 9–11 linear alcohol ethoxylate (LAE) non-ionic surfactant with an average of six ethylene oxide units per mole of alcohol were evaluated in 30-day exposures in 12 outdoor stream mesocosms by measuring changes in benthic invertebrate densities, invertebrate drift, and feeding rates of caged Hyalella azteca Saussure. Five surfactant concentrations were chosen for this study and the mean measured concentrations in duplicate streams were 0.73, 2.04, 4.35, 5.70, and 11.24 mg l −1 with two untreated streams as controls. Surfactant analyses showed that in-stream concentrations were similar to nominal values throughout the 30-day treatment period. There were statistically significant effects ( P l −1 . At 11.24 mg l −1 , reduction in benthic densities was accompanied by a dramatic increase in Copepoda collected in drift nets. There were no observed effects on densities or drift of other groups of aquatic invertebrates, including Nematoda, Diptera, and Amphipoda. In streams treated with 5.7 and 11.24 mg l −1 , feeding rates of caged Hyalella azteca on Acer rubrum (maple) leaf disks were significantly less than in the control streams. However, there were no significant effects observed when feeding rates were normalized for number of surviving H. azteca , demonstrating that LAE effects on feeding rates were linked with survival of H. azteca .