IN-SITU BIODEGRADATION OF TOLUENE IN A CONTAMINATED STREAM .2. LABORATORY STUDIES

In-situ biodegradation rates for a stream contaminated with toluene (< 350 mu g/L) were determined in laboratory experiments and compared to those determined in field studies within the same stream reported in the previous paper. The biodegradation rate constant obtained in batch studies (shake-flasks, 0.06-0.16 m/h) was comparable to the in-situ rate constant obtained in field studies (0.08-0.40 m/h) at similar temperature while the rate constant from column studies was only 2% of the in-situ rate constant. This data showed that the batch studies were better indicators oi in-situ biodegradation and also more accurately reflected field conditions. Streambed surfaces were responsible for virtually all degradation, with sediments and rocks providing the most important (> 95%)compartmental contributions. Rates determined in batch studies under winter conditions were 11-14% of rates determined under summer conditions. Batch,studies of mineralization rates determined with [U-C-14]toluene indicate that mineralization rates were 23% of biodegradation rates. The remaining toluene was converted to soluble intermediates (l5%) land 62% was taken up as biomass or converted to other insoluble material. Our results support the assertion that biodegradation was the most important environmental sink for toluene, with 70% of the toluene loss due to biodegradation over the studied stream reach.