Abiotic Reduction of Nitro Aromatic Pesticides in Anaerobic Laboratory Systems

Rapid abiotic reduction of nitro aromatic pesticides occurs in homogeneous solutions of quinone redox couples, which were selected to model the redox-labile functional groups in natural organic matter. The kinetics of methyl parathion disappearance are first order in methyl parathion and first order in the monophenolate form of the hydroquinone. The concentration of the monophenolate was calculated from electrode measurement of Eh and pH of the model system and thermodynamic data. The second-order rate constant at 25 °C is 31.1 ± 4.9 L min^-1mol^-1in a solution where the quinone-hydroquinone redox system consists of partially reduced indigo disulfonate and is (3.80 ± 0.65) X 10⁴L min^-1mol^-1in redox systems based on anthraquinonedisulfonate. Reduction of methyl parathion is negligible above about -50 mV; this is the apparent reduction potential of methyl parathion under the conditions used in this study. In indigodisulfonate model systems, the disappearance of profluralin is also second order but with a rate constant equal to 79.0 ± 8.6 L min^-1mol^-1.