Study of Analytical Techniques to Determine Chlorpyrifos in the Surface Waterways of the Rural Zone of Ouro Branco, Brazil: A Case Study

The presence of insecticides in the waterways of the municipality of Ouro Branco, MG, Southeastern Brazil, has become a public health problem. Recent research correlates the presence of these toxins in the water to the high indexes for hypertension and abortions occurring in the rural area. These insecticide residues are only slightly concentrated in the water, and as such, it is necessary to search for and optimize analytic methods that are capable of detecting these very low concentrations. To define the method that presents the best detectability for the organochlorine chlorpyrifos, one of the most used pesticides in the area, sample extraction techniques such as liquid–liquid extraction with low temperature partition (LLE-LTP) and headspace solid-phase microextraction (HS-SPME) were used, followed by gas chromatography analysis with electron capture detection (GC-ECD). Full factorial design 2⁴ and the Doehlert matrix were used to optimize both extraction techniques. The results displayed that HS-SPME-GC-ECD was the method that presented the best performance for determining the presence of chlorpyrifos in the water. The optimum condition was defined at the extraction time and temperature of 60 min and 85 °C, respectively, with a sample volume of 11 mL and Na₂HPO₄ concentration of 0.04 mol/L. The optimized method was validated for the principal figures of merit. The method displayed linearity with R ² equal to 0.992 and detection limit (LOD) and quantification limit (LOQ) of 0.50 and 1.67 μg/L, respectively. The results indicate that the HS-SPME-GC-ECD technique proposed is efficient for determining the presence of chlorpyrifos in water, and analyses of the collected sample indicated the presence of chlorpyrifos in water bodies in the rural zone of Ouro Branco in concentrations within detection and quantification limits.