SEASONAL TEMPERATURE DECLINES DO NOT DECREASE PERIPHYTIC SURFACTANT BIODEGRADATION OR INCREASE ALGAL SPECIES SENSITIVITY

The effects of seasonally decreasing river water temperature on surfac tant biodegradation and algal sensitivity are reviewed from four strea m mesocosm studies conducted over a 5-year period. Seasonal temperatur es ranged from 28 to 0 degrees C over all studies and temperature decl ines were approximately 9 to 14 degrees C over the course of each indi vidual study. Mesocosm periphyton were naturally colonized on tile sub strata with in-flowing river water for a period of 3 to 8 weeks prior to the initiation of sampling. Streams were dosed for 8 to 11 weeks wi th mu g/L (ppb) quantities of the surfactants C-12-alkyl sulfate (C-12 -AS), C45E2.17S-alkyl ethoxysulfate (AES), C25E6-alkyl ethoxylate (AE) or 0 to 13% final effluent during the sampling period. Mineralization of C-12-AS and AE by periphyton in the dosed streams generally increa sed over the dosing period while mineralization remained approximately constant in the control streams. The results from the AE study occurr ed with an increase in periphyton heterotrophic respiration. Mineraliz ation of AES increased over the dosing period in streams receiving the highest dose of AES and remained constant in streams receiving lower doses. All studies involving surfactant exposure demonstrated a positi ve correlation between surfactant concentration and mineralization dur ing periods of seasonal temperature decline. Mineralization of AE by p eriphyton dosed with final effluent increased slightly over the testin g period. Periphytic algal taxonomy and biovolume were evaluated durin g the AES study. Overall, these tests showed no increases in species s ensitivity over the testing period. Taken collectively, these results indicate that there is no correlation between naturally decreasing sea sonal temperatures and lower rates of surfactant mineralization or inc reased species sensitivity by naturally acclimated periphyton. (C) 199 7 Elsevier Science Ltd.