Photochemical degradation of methylparathion in the presence of humic acid

Abstract

Photochemical degradation of methylparathion (O,O,-dimethyl O-4 nitrophenylphosphorothioate) in the presence of humic acid between pH 2 and 7 was monitored by differential pulse polarography. Humic acid was not electro-active under the experimental conditions used in this study. Only the pesticide and its main degradation product at pH 2 exhibited polarographic signals. Photolysis of methylparathion in acid media was sensitized by humic acid since the pesticide did not degrade in the absence of this compound. Methylparathion degradation in the presence of humic acid was observed at each of the studied pHs. The reaction was first-order with rate constant values ranging from 2 x 10(-3) to 6.3 x 10(-3) min(-1).

Effect of fulvic acid on the photochemical degradation of methylparathion

“…Fulvic acid was separated from humic acid with a centrifuge (Zeigen 80-2). [11] Photolysis of methylparathion in the presence of fulvic acid was done with a reactor described in an earlier study. [18] Irradiation was done with a multiband ultraviolet lamp (Mineralight UVGL-58) at λ = 366 nm.…”

“…[11] Polarography was done in an aqueous medium with buffered pH. The pH buffer system was Britton Robinson (BR) described in a earlier study.…”

“…The pH buffer system was Britton Robinson (BR) described in a earlier study. [11] Solution pH was adjusted using HNO 3 at 65 % (Merck) or NaOH (J. T. Baker). Nitrogen gas (4.8, Infra) was used to eliminate oxygen from the analyzed solutions and to create an inert atmosphere for the photochemical reactions analysis.…”

“…[12] Other studies have included modeling of these reactions under controlled laboratory conditions. Manzanilla et al [11,13] reported on the photochemical degradation of methylparathion in the presence of the photosensitizers TiO 2 (pH 6.5) and humic acid (pH 2-7), in an aqueous medium and in the absence of oxygen. They observed that the main degradation products were p-nitrobenzoic acid and p-nitrophenol.…”

Water quality parameters controlling the photodegradation of two herbicides in surface waters of the Columbia Basin, Washington

“…DOM-sensitized photolysis has been shown to degrade a number of xenobiotics including trifluralin (Dimou et al, 2004), atrazine (Prosen and Zupancic-Krajl, 2005), imazaquin and iprodione (Garbin et al, 2007), alloxydim (Sevilla-Moran et al, 2008), and methyl parathion (Manzanilla-Cano et al, 2008).…”