The effects of a cationic surfactant were evaluated in field experiments with natural algal assemblages to validate the laboratory toxicity data base. Response parameters monitored in studies of 3 h to 21 days duration included structural and functional community characteristics in addition to more standard growth measurements. Photosynthesis and community similarity were typically the more sensitive parameters and a diversity index the least sensitive. The median effective concentration (EC50) values based on photosynthetic activity ranged from 0.4 to 6.1 mg/L. Phytoplankton were first affected in situ between 0.03 and 1.99 mg/L, relative to an effect level between 0.21 and 0.96 mg/L for periphyton. Periphyton colonized and exposed in river water containing 25% effluent were first affected at 6.9 mg/L. A mean in-stream concentration of 0.25 mg/L had no adverse effect on the indigenous periphyton of a small Indiana stream based on comparison of three-week pre- and post-exposure community analysis. Rapid biodegradation was observed in the field experiments.
The field-derived effect concentrations were compared with those determined in standard laboratory toxicity tests for four cultured algal species. The laboratory first-effect and EC50 levels for these single species were typically lower. Overall, the multispecies tests proved valuable in providing perspective on the potential for an environmental impact from this surfactant that could not be demonstrated in the laboratory using current standard testing methodologies.