A model stream ecosystem evaluation of the non-commercial alcohol ethoxylate 25-6 alcohol ethoxylate (AE) was performed in 1994. Algal, heterotrophic microbial, protozoan, and invertebrate communities were assessed over an 8-week exposure period that followed an 8-week colonization period. Streams were exposed to nominal concentrations of 0, 12, 37, 111, 333 and 1000 mu g AE/l. Confirmed concentrations (8-week means) were 7 (at the detection limit), 13, 36, 76, 259, and 760 mu g AE/l as measured at the head of streams on a weekly basis. Microbial communities were initially enhanced by AE exposure (first 2 weeks of exposure), but by the conclusion of the study autotrophic and heterotrophic microbial communities were similar across treatments. In contrast, invertebrate populations and communities responded strongly to AE exposure with adverse effects indicated at 259-760 mu g/l by 4 weeks and at 36-760 mu g/l by 8 weeks. Key affected groups were the sensitive mayfly, stonefly, and caddisfly fauna. Species richness and abundance of selected populations such as Stenonema (mayfly), Chimarra a (caddisfly), and Corbicula (Asiatic clam) were affected. These data indicated a model ecosystem no-observed effect concentration of 13 mu g/l for 25-6 AE. In contrast to other published AE model ecosystem studies, 25-6 appears more toxic. Structure-activity-relationships at the model ecosystem level still demonstrate good relationships across a range of surfactants with calculated K(ow)s of 3-6. Importantly, the collective information on fate and effects measured in laboratory and field systems confirms low risk to the environment. (C) 2000 Elsevier Science B.V. All rights reserved.
