Determination of 2,4-Dichlorophenoxyacetic Acid and Its Metabolite in Soils by Gas Chromatography–Mass Spectrometry after Preconcentration Using Magnetic Charcoal Based on Rice Husk

Abstract

A method is proposed for determining 2,4-dichlorophenoxyacetic acid (2,4-D) and its metabolite, 2,4-dichlorophenol (2,4-DCP), in soils. 2,4-D and 2,4-DCP are isolated from soil by extraction with an alkali solution. The analytes are extracted from the extract using a sorbent based on magnetite nanoparticles and carbon obtained by burning rice husk, and desorbed with methanol. In the resulting concentrate, 2,4-D and 2,4-DCP are converted into methyl esters and determined by GC–MS. The limits of detection for 2,4-D and 2,4-DCP are 3.0 and 0.08 μg/kg, respectively. Leached chernozem (border of Stavropol and Krasnodar Krais) is chosen as a real soil for analyzing the distribution of the Ballerina herbicide (2,4-D ethylhexyl ester) and its degradation product. One day after the herbicide application, the concentration of 2,4-D in the surface soil layer is 119 μg/kg. Precipitation has a significant effect on the movement of 2,4-D along the soil profile. The greatest decrease in the concentration of 2,4-D is found between 3 and 10 days after the herbicide application. One month after the herbicide application, the 2,4-D concentrations are 31, 18, and 11 μg/kg at depths of 10, 30, and 50 cm, respectively; 2,4-D is not detected in the surface soil layer. 2,4-DCP is present in detectable quantities on the 16th day after the herbicide application; its degradation is significantly slower than that of 2,4-D. After 1.5 months, the 2,4-DCP concentrations are 0.53, 0.45, and 0.22 μg/kg at the depths 10, 30, and 50 cm, respectively. During the same period, 2,4-D is not detected throughout the soil profile.