IN-SITU BIODEGRADATION OF TOLUENE IN A CONTAMINATED STREAM .1. FIELD STUDIES

In-situ toluene biodegradation rates in a stream were determined throu ghout the year using a mass balance approach in which sodium chloride and propane tracers accounted for dilution and volatilization, respect ively, and allowed biodegradation rates to be estimated. Dilution, vol atilization, and biodegradation accounted for 25%, 34%, and 41% of the decrease in totuene concentration in the high flow season (spring), r espectively, and 8%, 26%, and 66% in the low flow season (summer). Vol atilization rate constants of toluene were estimated as 0.62 h(-1) in summer and 0.20 h(-1) in winter, while biodegradation rate constants w ere 1.73 h(-1) in summer and 0.20 h(-1) in winter. Our results show th at biodegradation was the most significant sink for toluene in the str eam throughout the year. The benthic uptake rate constant of toluene r anged from 0.03 m/h in winter to 0.21 m/h in summer. Biodegradation ra te constants were strongly dependent on stream temperature, but were u ncorrelated or weakly correlated with stream velocity.