Adaptation of periphytic communities in model streams to a quaternary ammonium surfactantt

The ability of periphytic communities to mineralize the quaternary ammonium surfactant dodecyltrimethylammonium chloride (C12TMAC) was studied in model streams receiving river water amended with 10% final effluent from a sewage treatment plant. In August 1989, clay substrata were placed in each streambed and allowed to colonize with periphyton for three weeks. Subsequently, three streams were continuously dosed with 50, 250, or 1,250 μg/L C12TMAC for an eight-week period, while a fourth stream served as an undosed control. Before dosing, half-lives for mineralization of radiolabeled C12TMAC by periphyton from the model streams were approximately 5 d, and C12TMAC turnover times were >3,000 h. After dosing with surfactant, mineralization half-lives for C12TMAC by periphyton decreased to 0.03 d within four weeks, and turnover times declined to 6 h within six weeks. By contrast, half-lives for mineralization of C12TMAC by periphyton in the untreated control stream increased from 5 to 29 d, and turnover times remained at >3,000 h during the eight-week test period. Results from a similar experiment conducted during the spring of 1990 confirmed a rapid adaptation of periphytic communities to C12TMAC. This study demonstrated that periphytic communities adapted to and mineralized C12TMAC upon exposure under simulated in situ conditions.