RESIDUES AND TRACE ELEMENTS Liquid Chromatographic–Diode-Array Detection Multiresidue Determination of Rice Herbicides in Drinking and Paddy-Field Water RAFAEL ROEHRS and RENATO ZANELLA Universidade Federal de Santa Maria, Laboratório de Análise de Resíduos de Pesticides, Avda. Roriama 1000, Campus Carnobi, 97105-900, Santa María, Rio Grande do Sul, Brazil IONARA PIZZUTI Universidade Federal de Santa Maria, Centro de Pesquisa e Análise de Resíduos e Contaminants, Avda. Roriama 1000, Campus Carnobi, 97105-900, Santa María, Rio Grande do Sul, Brazil MARTHA B. ADAIME Universidade Federal de Santa Maria, Laboratório de Análise de Resíduos de Pesticides, Avda. Roriama 1000, Campus Carnobi, 97105-900, Santa María, Rio Grande do Sul, Brazil LUCÍA PAREJA, SILVINA NIELL, MARÍA V. CESIO, and HORACIO HEINZEN 1 Universidad de la República, Farmacognosia y Productos Naturales, Gral. Flores 2124, 11800, Montevideo, Uruguay A sensitive, rapid, and simple multiresidue method for the simultaneous determination of six postemergence herbicides currently used in rice cultivation—metsulfuron methyl, bensulfuron methyl, pyrazosulfuron ethyl, bentazone, bispyribac sodium, and cyhalofop butyl—in drinking and paddy-field water is presented. Water samples were extracted with solid-phase extraction cartridges. Final determination was made by LC with diode-array detection. The extraction efficiencies of C18 and HLB cartridges were compared. The average recovery obtained for these compounds for the lowest spiked level (0.1 mg/L) varied from 70 to 122% for C18 and 75–119% for HLB, with RSDs of 11 and 8.3%, respectively. The method had good linearity, and the lower detection limit for the pesticides studied varied from 0.03 to 0.04 mg/L. The proposed method was also tested in paddy-field water, with recovery studies giving good results with low RSDs at 1.0 mg/L. H erbicides are chemicals designed to kill plants, either selectively or nonselectively, and they comprise more than half of the pesticides employed in agriculture worldwide. Because herbicide molecules are toxic to a greater or lesser extent, they represent not only an environmental risk, but also a health hazard (1). They usually have high mobility in water and soil (2, 3) and can be found far away from the places where they were applied. This is of paramount importance in rice crop production. As a result of the irrigation systems currently used in rice cultivation, it is possible both for cross-contamination between agrochemicals to occur and for these chemicals to spread even to fields where no pesticides have been applied. The postemergence herbicides currently used in the “technological package” for rice crops have different chemical origins: sulfonylureas (metsulfuron methyl, bensulfuron methyl, pyrazosulfuron ethyl), bentazone, bispyribac sodium, and cyhalofop butyl. These herbicides are used at very low doses (<100 g/hectare) and are chemically unstable (in water, time for 50% decline of the initial pesticide concentration = 1–2 months; 4), which makes their determination in environmental water a real analytical challenge. LC–diode-array detection (LC-DAD) has been used for the determination of herbicide residues in surface and groundwaters (5, 6). Sulfonylureas (7, 8), bentazone (9–12), and bispyribac sodium have also been analyzed in water, but no method has been reported for the simultaneous determination of all the herbicides currently used in rice production. Therefore, it is desirable to develop a multiresidue method for the analysis of these herbicides that can either be expanded to include other herbicides and agrochemicals, or be applied to different matrixes of rice production systems, such as water, soil, and grain. In this communication, we present an accurate, reproducible, and sensitive LC-DAD method for the simultaneous determination of these herbicides, which account for 45% of the total of postemergence herbicides used in Uruguay. In addition, the levels of these herbicides need to be determined because of their toxicity. Bentazone was banned by the European Union, and the World Health Organization suggests an oral intake of less than 2 mg/L per person/day. Even though the toxicity of these chemicals is not unduly alarming in mammals, it can be dangerous to other species (13). 1190 ROEHRS ET AL.: JOURNAL OF AOAC INTERNATIONAL VOL. 92, NO. 4, 2009 Received September 1, 2008. Accepted by AK October 30, 2008. 1 Corresponding author’s e-mail: heinzen@fq.edu.uy