EVALUATION OF A LABORATORY-GENERATED NOEC FOR LINEAR ALKYLBENZENE SULFONATE IN OUTDOOR EXPERIMENTAL STREAMS

Laboratory and field studies were conducted with linear alkylbenzene s ulfonate (LAS) to evaluate the use of laboratory-generated NOECs for p rotecting aquatic organisms in outdoor experimental streams. Fathead m innows (Pimephales promelas) and freshwater amphipods (Hyalella azteca ) were exposed in the laboratory to an environmentally realistic mixtu re of LAS (average chain length C-11.9) for 7 d; fathead minnows were also exposed in a 28-d study. Calculated NOEC values based on survival and growth ranged from 0.3 to 0.9 mg/L for fathead minnows and from 0 .6 to 1.4 mg/L for amphipods. Toxicity of LAS in 4-, 7-, and 28-d expo sures of fathead minnows was similar because mortality occurred within the initial 24 h of exposure; mortality was more sensitive than growt h as a chronic end point. The addition of 5% sewage effluent to well a nd stream water had little effect on the bioavailability of LAS; howev er, total organic carbon levels were low (<3 mg/L) in all treatments. A 45-d exposure of three outdoor experimental streams to 0.36 mg/L LAS had no effects on survival of fathead minnows or amphipods, dynamics of benthic invertebrates, growth of periphyton, or processing of detri tal leaves. Results indicated that the laboratory-generated NOEC for L AS was protective of experimental stream communities under the studied conditions.