| Benzotriazoles are the most widely used type of industrial corrosion inhibitor. Benzotriazole derivatives are present in high concentrations in deicing fluids, industrial cooling water systems, and antifreeze. A recent USGS reconnaissance of 139 freshwater streams nationwide, found that 1/3 of them contained 5-Methylbenzotriazole (MeBT) in significant concentrations. Literature on the biological activity of benzotriazoles is dated and tenuous.; The environmental behavior of benzotriazoles derivatives remains largely unknown. To investigate the biotransformation potential of the most commercially significant benzotriazole derivatives—4- and 5-MeBT—biodegradation experiments were conducted with activated sludge and bacteria enriched from airport soils contaminated with aircraft deicing fluids. Below a toxic threshold (c.a. 100 mg/L), all enrichments were capable of degrading 5-MeBT under aerobic conditions, however, over a 24-month period, 5-MeBT was recalcitrant under anoxic, and 4-MeBT was recalcitrant under all conditions tested. Respirometry experiments provided evidence that MeBT may behave as an uncoupler to pure cultures of Pseudomonas aeruginosa. Oxygen uptake and biomass monitoring showed bacterial growth on propylene glycol and glucose was limited by the presence of MeBT, yet oxygen uptake rates of cell fragments remained the same or increased when MeBT levels were at or above 300 mg/L. Uncoupling behavior was not evident on mixed cultures grown from enrichments of soil bacteria taken from airport soils contaminated with aircraft deicing fluids and acclimated to propylene glycol. However, inhibitory effects were apparent in these cultures at MeBT concentrations greater than 200 mg/l suggesting that the main toxicity mechanism appears to be associated with respiratory chain activity. Using fluorometric membrane potential dyes [DiBAC], direct epifluorescent microscopy of bacterial cells exposed to MeBT confirmed that these benzotriazoles could attenuate the transmembrane potential of active bacterial membranes.; 5-MeBT was completely mineralized by activated sludge and enrichments of soil bacteria. Only the acclimated soil enrichment cultures were able to use this benzotriazole derivative as a sole carbon and nitrogen source. Two pure bacteria cultures were isolated by using 5-MeBT as a sole carbon source. They were tentatively identified as Pseudonocardia alni and Variovorax sp. (16sRNA). |
