Degradation of Paraquat in the Aquatic Environment: A proposed Enzymatic Kinetic Model that takes into account adsorption/desorption of the Herbicide by Colloidal and Sediment Particles
Journal Title: International Journal of Research in Chemistry and Environment (IJRCE) - Year 2013, Vol 3, Issue 3
Abstract
The kinetics of the degradation of paraquat in an aquatic microcosm environment charged with the herbicide were studied over a period of 70 days. Distilled water charged with the herbicide and boric acid preservative was used as control. The concentration of paraquat was monitored in the distilled water control, as well as the water phase and sediment phase of the experiment. An immediate 31.8% loss of paraquat from the microcosm experiment was observed soon after charging due to adsorption by the sediment. Subsequently, biphasic linear rates of paraquat degradation were observed for both the water phase (1.52 x 10-3 and 1.3 x 10-4 mg/mL/day) and sediment phase (1.81 x 10-2 and 3.41 x 10-3 mg/g/day). The distilled water control showed a minimal degradation rate of 7 x 10-5 µg/mL/day during the first 35 days, attributed to abiotic degradation, followed by a slightly faster linear degradation rate of 2.6 x 10-4 mg/mL/day. The slow linear rate of degradation in distilled water is attributed to photochemical degradation, while the subsequent slightly faster rate is attributed to microbial degradation. The linear rates of degradation in experimental microcosm are attributed to microbial degradation, and an enzymatic kinetic model that takes into account adsorption/desorption of the herbicide by colloidal and sediment particles is presented to account for the observed kinetics.
Authors and Affiliations
Zaranyika M. F. , Nyoni S.
Keywords
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