Effect of Fe (III) on acid degradation of methylparathion
A study was undertaken to determine the transformation kinetic of methylparathion (O, O, -dimethyl O-4 nitrophenylphosphorotioate) in the presence of Fe(III) between pH 2 and 7. The Fe(III) was not electroactive under the conditions used in this study, and polarographic signals were exhibited by methylparathion and main degradation product only. Data suggest that hydrolysis of methylparathion in an acid medium is catalyzed by Fe(III) and the pesticide did not degrade in this medium without this cation. Methylparathion degradation was observed at all the pHs studied and was independent of the predominant chemical form of Fe(III) in the aqueous medium. The reaction was first-order with pH-dependent rate constant (k) values ranging from 3.3 × 10− 3 h− 1 to 7.0 × 10− 3 h− 1. The k values increased as pH decreased, suggesting that Fe(III) acted as an electrophile in the reaction mechanism.
Effect of fulvic acid on the photochemical degradation of methylparathion
Photochemical degradation of methylparathion (O,O,–dimethyl O-4 nitrophenylphosphorothioate) in the presence of fulvic acid (FA) between pH 2 and 7 was studied by differential pulse polarography (DPP). Fulvic acid and its photoproducts were not electro-active under the experimental conditions used in this study, and only the pesticide exhibited polarographic signals. Photolysis of methylparathion in acid media was sensitized by fulvic acid since the pesticide did not degrade in the absence of this compound. Methylparathion degradation was observed at each of the studied pHs. The reaction was first-order with rate constant values ranging from 3.3 × 10−3 to 8.8 × 10−3min−1.
Sorption and Bound Residue Formation of Linuron, Methylparathion, and Metolachlor by Carrot Tissues: Kinetics by On-Line HPLC Microextraction
The feasibility of determining the identities and kinetics behavior of three pesticides in carrot tissue slurries using a novel on-line HPLC microextraction was investigated. Linuron, methylparathion, and metolachlor were added to aqueous slurries of carrot tissue particles smaller than 150 μm. For each pesticide, the solution phase and the total pesticide recoverable from the whole slurry concentrations were separately monitored over a 10 day period. Kinetics curves for three categories of chemical species including solution phase pesticides, labile sorbed fractions, and unrecovered fractions were obtained. The linuron and metolachlor data are consistent with the commonly reported two-step sorption mechanism consisting of labile sorption followed by intraparticle diffusion, but the methylparathion data resemble a combination of labile surface sorption and solution phase and/or surface chemical decomposition. It is concluded that laboratory test methods of this type could be developed for assessing the ri...