Evaluation of glyphosate formulations residues in glyphosate-tolerant soybean by high-performance liquid chromatography (HPLC)

Abstract

The liberation of the use of the transgenic glyphosate-tolerant soybean (GTS) in Brazil generated a wide scientific discussion on the accumulation of residues of the herbicide glyphosate in the soy grains. The controversy is being reinforced by analyses accomplished in samples collected in the harvest 2005/2006, which present values close to 10 mg kg-1, current limit maximum of residues (LMR). The human food security is the main justification for the identification and the quantification of glyphosate residues in the grains of this oleaginous, due to the consumption in wide scale of derived products of soy for the Brazilian population and for government programs to increase the demand of soy in natura and to supply proteins through the offer of soy milk in public schools. There is the need of the inclusion of different formulations containing glyphosate in the researches, because different concentrations of the active ingredient and surfactants can result in variations in the residues levels. This project is part of thesis of Guilherme Pires D Ávila de Almeida. The aim of the present work is to determine, with the aid of high performance liquid chromatography (HPLC), the residual amount of glyphosate and of its main metabolite, aminomethylphosphonic acid (AMPA), in the grains of GTS, after over-the-top application of some formulations in different development stages of the culture under field conditions. All of the analyses will be accomplished at the Laboratório de Ecotoxicologia of the Centro de Energia Nuclear na Agricultura (CENA/USP) in a HPLC equipment. The development of the soy plants will happen under field conditions during all its cycle, approximately 120 days, in Fazenda Areão, of the Escola Superior de Agricultura "Luiz de Queiroz" (ESALQ/USP) in Piracicaba,SP Brazil. The experiment will be replicated inside of the preferential period of the planting of soy that comes to be used, however in case they happen operational problems, the replica will be accomplished the following year, in the same time recommended for the planting. The experimental design will be ia split-plot design with four blocks: the plots will be called herbicide program, combination of the dose with the application time, and the different formulations (treatments) will be the subplots. The four blocks will have one of the four repetitions of each plot, that it will be completely randomized. Each plot will contain one of the four repetitions of each subplot, also entirely randomized. In each plot, there will be a control subplot that will not receive application. All the data will be submitted to ANOVA, that will be processed by the SAS program. The herbicide programs, formulations and application times will be tested in agreement with all of the possible interactions. The averages of the treatments, when the test F is significant, they will be compared by the test of Tukey, in the 5% significance level. All of the treatments will have as reference the largest doses for the formulation Roundup Ready (Monsanto of Brazil Ltd.) recommended for unique or sequential application, wich are described in the approved label for the Ministério da Agricultura, Pecuária e Abastecimento. Treatments: control (without application) and formulations Rodeo, Roundup Original, Roundup WG and Roundup Ready; doses and application times: 1,2 kg ha-1 of equivalent acid (e.a.) to the 20 days after the emergency (dae); only application of 1,2 kg ha-1 e.a. to the 30 dae; application of 0,96 kg ha-1 e.a. to the 20 dae with sequential application of 0,72 kg ha-1 e.a. to the 35 dae; application of 0,96 kg ha-1 e.a. to the 30 dae with sequential application of 0,72 kg ha-1 e.a. to the 45 dae. (AU)