Electroanalytical procedure for the determination of methylparathion in soil suspensions and its application for sorption studies with Brazilian soils

Abstract

A técnica de polarografia de pulso diferencial foi usada para estabelecer um procedimento eletroanalítico para a determinação do inseticida organofosforado parathion metílico (tiofosfato de dimetilparanitrofenila) em amostras de solo. Foram observados 3 picos de redução do metilparathion sobre eletrodo de mercúrio, em função do pH da solução. O pico mais catódico (Ep = -0,55 V), observado apenas em pH's maiores que 5,0, foi selecionado para as determinações analíticas. O limite de detecção encontrado foi de 1,93x10 -8 mol L -1 para água pura e de cerca de 8x10 -8 mol L -1 para as amostras de solo, com velocidade de varredura de 2 mV s -1 e pH da solução de 6,75. O procedimento eletroanalítico desenvolvido foi utilizado para a obtenção de isotermas de sorção do parathion metílico em 3 solos do Estado de São Paulo, com distintos teores de argila, matéria orgânica e pH. O modelo de isoterma de Freundlich apresentou um excelente ajuste aos dados experimentais e os coeficientes de Freundlich (K F ) obtidos para cada solo apresentaram valores entre 7 e 29 L kg -1 , sendo considerados como de baixa a média capacidade de sorção nos solos estudados, de acordo com o critério do IBAMA (Instituto Brasileiro de Meio Ambiente e dos Recursos Renováveis). Os teores de matéria orgânica e argila dos solos foram os fatores que mais influenciaram a sorção do metilparathion nesses solos.The differential pulse polarography technique was used to establish an electroanalytical procedure for the determination of the organophosphorous insecticide methyl parathion (O,O-dimethyl O-(4-nitrophenyl) phosphorothioate) in soil samples. Three reduction peaks were observed in mercury electrodes as a function of the solution pH. The more cathodic peak (E p = -0.55V), only observed for pH values higher than 5.0, was chosen for the analytical determinations. The limit of detection was 1.93x10 -8 mol L -1 for pure water and about 8x10 -8 mol L -1 for soil suspensions with a scan rate of 2 mV s -1 and a pH of 6.75. The electroanalytical procedure developed was applied for the determination of sorption isotherms of methylparathion on 3 soils from São Paulo State, Brazil, at different pH and diverse amounts of clay and organic matter. The experimental data were fitted using the Freundlich isotherm model and the Freundlich coefficients (K F ) obtained for each soil varied from 7 to 29 L kg -1 , representing a low to medium sorption capacity, according to the IBAMA (Brazilian Environmental Protection Agency) standards. The amounts of organic matter and clay were the most important soil parameters controling the sorption of methylparathion by these soils.

Study of the Electrochemical Behavior and Sensitive Detection of Pesticides Using Microelectrodes Allied to Square-Wave Voltammetry

“…Methyl parathion (O,O-dimethyl-O-(4-nitrophenyl)-phosphorothioate) is a organophosphorous insecticide very effective against many pests in important crops such as bulbs, cereals, fruits, vegetables, cotton, peanuts, soybean, potato, sugar cane, coffee, alfalfa and pasture [27]. Similar to dichlorvos, methyl parathion is an inhibitor of acetylcholinesterase, therefore, producing serious damage and death, also it is considered extremely toxic.…”

Electrochemical behavior of parent and photodegradation products of some selected pesticides

“…4,6,22,23 The methylparathion, imazaquin and atrazine present reduction reactions at the mercury electrode with best analytical responses at pH 6.5, 3.0 and 2.3, respectively. Bentazon is electroactive on glassy carbon electrode in acidic medium, but the complex oxidation mechanism causes severe adsorption problems and consequent poisoning of the electrode surface.…”

Voltammetric Analysis of Pesticides

“…In this study, both standard addition and calibration methods were used to determine folfet and phosmet at nanomolar level. Castanho et al (2003) developed a differential pulse polarographic method to detect methylparathion in water and soil suspensions. Their method allowed the recording of the sorption isotherms of the pesticides on three Brazilian soils.…”