A stream mesocosm study on the ecological effects of a C12-15 linear alcohol ethoxylate surfactant

The responses of fish, invertebrates, and periphyton during a 56-day exposure to a C(12-15) linear alcohol ethoxylate surfactant were studied in stream mesocosms. An individual stream consisted of a slow-flowing pool section and a faster-flowing riffle section. The surfactant has an average distribution of nine ethoxylate groups per mole of alcohol. Eight stream mesocosms were used to test the effects of seven concentrations of the surfactant. Time-averaged, mean, measured concentrations were 20, 40, 70, 160, 300, 390, and 740 microg/L, which represented 70-100% of nominal concentrations. The exposure of aquatic communities to the C(12-15)AE-9 surfactant in stream mesocosms resulted in no-observed-effect concentrations (NOECs) for individual endpoints ranging from 160 to 740 microg/L. Among the more sensitive responses were Oncorhynchus mykiss time to swim up and fry growth, abundance of juvenile Gammarus pulex in drift samples, Baetis abundance in the riffle sediment and in samples collected from tiles placed in the riffle, and Simulium density in the riffle tiles, all with NOECs of 160 microg/L. Responses of the riffle sediment invertebrate assemblages assessed using multivariate methods support a NOEC of 160 microg/L. Abundances of G. pulex, Copepoda, and Agapetus sampled in the pools and pool tiles were not affected at the highest surfactant concentration tested after 56 days. Surfactant effects on periphyton and community leaf processing were seen at 300-390 microg/L. Based upon the responses of several taxa representing different trophic levels, a mesocosm NOEC of 160 microg/L can be stated for the C(12-15)AE-9 surfactant. This study provided additional data that can be used to reduce the uncertainty in extrapolating laboratory data to the field for the environmental risk assessment of alcohol ethoxylates.