Kinetics of biodegradation of nitrilotriacetic acid (NTA) in an estuarine environment.

The effects of salinity and dissolved organic carbon (DOC) on the kinetics of biodegradation of nitrilotriacetic acid (NTA) were studied in a Canadian estuary with a prior history of NTA exposure. Kinetic parameters for degradation of 14C-labeled NTA, maximum velocity (Vmax) and first-order rate constant (k1), were estimated by nonlinear regression models from velocity and time-course plots, respectively. The distribution of bacteria with NTA-degrading capability was also determined at various salinities and DOC levels by the 14C-most-probable-number (14C-MPN) technique. In general, NTA degradation was rapid in estuarine water over the range of salinities and DOC levels tested. Mean Vmax and k1 values (+/- standard deviation) across several sampling periods averaged 4753 +/- 2849 ng liter-1 hr-1 and 0.32 +/- 0.19 day-1, respectively. The estimated half-life for NTA degradation in estuarine water, based on the mean k1 value, was approximately 2 days. Degradation rates for NTA were relatively insensitive to changes in salinity or DOC values, and neither of these two parameters had significant effects on NTA degradation at the microbial community or individual cell levels. Based on 14C-MPN results, the distribution of estuarine bacteria capable of degrading NTA was broad and not related to salinity or DOC levels. The NTA degraders appeared to be indigenous members of the estuarine microbial community and not wastewater-associated microorganisms.