RESPONSES OF AQUATIC INVERTEBRATES TO A LINEAR ALCOHOL ETHOXYLATE SURFACTANT IN STREAM MESOCOSMS

Responses of aquatic invertebrates to 30-day exposures to a nonionic l inear alcohol ethoxylate (LAE) surfactant (C(12-13)AE-6.5) were evalua ted in 10 outdoor stream mesocosms. Responses were measured as changes in invertebrate densities and invertebrate drift densities during a 1 4-day pretreatment period, a 30-day treatment period, and a 14-day pos ttreatment period relative to untreated control stream densities. Mean measured surfactant concentrations in duplicate streams were 0.32, 0. 88, 1.99, and 5.15 mg LAE/liter, with two streams serving as untreated controls. Statistically significant effects were observed on simulid, copepod, and cladoceran population densities during the treatment per iod. Based on these effects, the no-observed-effect concentration (NOE C) for invertebrate densities was <0.32 mg LAE/liter and the lowest-ob served-effect concentration (LOEC) was 0.32 mg LAE/liter. No statistic ally significant differences due to treatment were detected in driftin g invertebrates; however, a trend was observed with increased numbers of invertebrates drifting in the streams treated with 5.15 mg LAE/lite r as compared with controls. (C) 1998 Academic Press.