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 C12-13 linear alcohol ethoxylate (LAE) wer e studied in stream mesocosms. The surfactant has an average distribut ion of six and one-half ethylene oxide groups per mole of alcohol. Res ponses of periphyton, macrophytes, invertebrates, and fish were examin ed and used to estimate a mesocosm-predicted no-observable-effect conc entration (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 st reams were used along with two untreated control streams. Surfactant c oncentrations were delivered to the streams with no apparent loss duri ng the 17-min transit time. The structural integrity of the surfactant was also maintained with no observed differences between the head, mi ddle, or tail sections of individual streams. Average measured concent rations of LAE for replicate streams were 0.32, 0.88, 1.99, and 5.15 m g/L. Periphyton and Myriophyllum aquaticum did not show significant ef fects. The no-observed-effect concentration (NOEC) for all periphyton and M. aquaticum parameters was 5.15 mg/L, the highest concentration t ested. Statistically significant effects were observed on Simuliidae, Copepoda, and Cladocera densities during the treatment period in all e xposure concentrations. Thus, the lowest-observed-effect concentration (LOEC) for invertebrate densities was 0.32 mg/L. Drifting invertebrat es 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 pop ulations of fish were 0.88 mg/L and 1.99 mg/L, respectively. There wer e no significant effects on reproduction in University-cultured fathea d minnow. Fathead minnow reproductive behavior and feeding behavior we re most susceptible to surfactant exposure with a NOEC of 0.32 mg/L. B luegill sunfish survival responded similarly to the LAE as fathead min now with a 30-d NOEC of 0.88 mg/L. No sublethal effects on juvenile bl uegill growth were observed in this study. For primarily regulatory pu rposes, a ''mesocosm NOEC'' of 0.28 mg/L was derived for use in risk a ssessment.