In situ response of natural periphyton to an anionic surfactant and an environmental risk assessment for phytotoxic effects

In situ toxicity tests were conducted to determine the toxicity of linear alkyl- (dodecyl-) benzenesulfonate (LAS) on a natural periphyton community. Colonized periphyton were exposed to C11 9-LAS in 21-d continuous-flow toxicity studies conducted in the Little Miami River (Ohio) above and below a wastewater treatment plant outfall. The lowest measured first-effect levels were 3.3 and 16.6 mg/L, respectively, in the two locations, based on reductions in structural and functional community characteristics. The presence of 20 to 30% effluent did not increase the toxicity of LAS. The field-derived effect levels confirmed the low phytotoxicity observed in most previously conducted laboratory toxicity studies with cultured algae. In addition, the field-derived effect levels exceeded measured environmental concentrations, which supports the environmental safety of LAS to periphyton.