The effects of a C 12–13 linear alcohol ethoxylate surfactant on periphyton, macrophytes, invertebrates and fish in stream mesocosms

The ecological effects of a C 12–13 linear alcohol ethoxylate (LAE) were studied in stream mesocosms. The surfactant has an average distribution of six and one‐half ethylene oxide groups per mole of alcohol. Responses of periphyton, macrophytes, invertebrates, and fish were examined and used to estimate a mesocosm‐predicted no‐observable‐effect concentration (NOEC). The stream mesocosm experiment consisted of a 2‐week period of natural colonization, a 30‐d treatment period, and a 2‐week post‐treatment period. Four surfactant concentrations in duplicate streams were used along with two untreated control streams. Surfactant concentrations were delivered to the streams with no apparent loss during the 17‐min transit time. The structural integrity of the surfactant was also maintained with no observed differences between the head, middle, or tail sections of individual streams. Average measured concentrations of LAE for replicate streams were 0.32, 0.88, 1.99, and 5.15 mg/L. Periphyton and Myriophyllum aquaticum did not show significant effects. The no‐observed‐effect concentration (NOEC) for all periphyton and M. aquaticum parameters was 5.15 mg/L, the highest concentration tested. Statistically significant effects were observed on Simuliidae, Copepoda, and Cladocera densities during the treatment period in all exposure concentrations. Thus, the lowest‐observed‐effect concentration (LOEC) for invertebrate densities was 0.32 mg/L. Drifting invertebrates did not show significant LAE effects; however, increased numbers of invertebrates drifted in the 5.15‐mg/L streams compared to controls. The 30‐d LC50 for farm‐raised and University‐cultured fathead minnows was similar at 1.27 mg/L. The 30‐d survival NOEC and LOEC for both populations of fish were 0.88 mg/L and 1.99 mg/L, respectively. There were no significant effects on reproduction in University‐cultured fathead minnow. Fathead minnow reproductive behavior and feeding behavior were most susceptible to surfactant exposure with a NOEC of 0.32 mg/L. Bluegill sunfish survival responded similarly to the LAE as fathead minnow with a 30‐d NOEC of 0.88 mg/L. No sublethal effects on juvenile bluegill growth were observed in this study. For primarily regulatory purposes, a “mesocosm NOEC” of 0.28 mg/L was derived for use in risk assessment.