Environmental behaviors of (<i>E</i>) pyriminobac-methyl in agricultural soils

<p><span class="inline-formula"><i>E</i></span> or pyriminobac-methyl (EPM), a pyrimidine benzoic acid esters herbicide, has a high potential as weedicide; nevertheless, its environmental behaviors are still not well understood. In this study, we systematically investigated, for the first time, the adsorption–desorption, degradation, and leaching behaviors of EPM in agricultural soils from five exemplar sites in China (Phaeozems – <span class="inline-formula"><i>S</i>₁</span>; Anthrosol – <span class="inline-formula"><i>S</i>₂</span>; Ferralsol – <span class="inline-formula"><i>S</i>₃</span>; Alisol – <span class="inline-formula"><i>S</i>₄</span>; Plinthosol – <span class="inline-formula"><i>S</i>₅</span>) through laboratory simulation experiments. Our results show that the EPM adsorption–desorption results were well fitted by the Freundlich model (<span class="inline-formula"><i>R</i>²<i>&gt;</i>0.9999</span>). In the analyzed soils, the Freundlich adsorption (i.e., <span class="inline-formula"><i>K</i>_f ads</span>) and desorption (i.e., <span class="inline-formula"><i>K</i>_f des</span>) coefficients of EPM varied between 0.85 and 32.22 mg<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><msup><mi/><mrow><mn mathvariant="normal">1</mn><mo>-</mo><mn mathvariant="normal">1</mn><mo>/</mo><mi>n</mi></mrow></msup></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="26pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="f00be694fc1cd446b33ab7313474272f"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="soil-8-237-2022-ie00001.svg" width="26pt" height="11pt" src="soil-8-237-2022-ie00001.png"/></svg:svg></span></span> L<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><msup><mi/><mrow><mn mathvariant="normal">1</mn><mo>/</mo><mi>n</mi></mrow></msup></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="16pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="7e0bec708e28ccd566f3c6a6d53000dc"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="soil-8-237-2022-ie00002.svg" width="16pt" height="11pt" src="soil-8-237-2022-ie00002.png"/></svg:svg></span></span> kg<span class="inline-formula">⁻¹</span> and 0.78–5.02 mg<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M15" display="inline" overflow="scroll" dspmath="mathml"><msup><mi/><mrow><mn mathvariant="normal">1</mn><mo>-</mo><mn mathvariant="normal">1</mn><mo>/</mo><mi>n</mi></mrow></msup></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="26pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="2837478e44fa2f04afd915a5bf6658f1"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="soil-8-237-2022-ie00003.svg" width="26pt" height="11pt" src="soil-8-237-2022-ie00003.png"/></svg:svg></span></span> L<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><msup><mi/><mrow><mn mathvariant="normal">1</mn><mo>/</mo><mi>n</mi></mrow></msup></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="16pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="37f1b14ee811e1159b86bd74c9da8085"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="soil-8-237-2022-ie00004.svg" width="16pt" height="11pt" src="soil-8-237-2022-ie00004.png"/></svg:svg></span></span> kg<span class="inline-formula">⁻¹</span>, respectively. The mobility of EPM in soils <span class="inline-formula"><i>S</i>₁</span>–<span class="inline-formula"><i>S</i>₅</span> was categorized as immobile, slightly immobile, highly mobile, slightly mobile, and slightly mobile, respectively. Moreover, the degradation of EPM reflected first-order kinetics, where its half-life ranged between 37.46 and 66.00 d, depending on the environmental conditions, and abiotic degradation was predominant in the degradation of this compound. Overall, the high leaching ability and desorption capacity of EPM were accompanied by a low adsorption capacity, and there were no significant relationships between pH and the leaching rate of EPM in the five types of soils. In contrast, the organic matter content, cation exchange capacity, and soil clay content were the main components responsible for the observed leaching rates. We found that EPM degrades easily, has a high adsorption affinity, and a low mobility in <span class="inline-formula"><i>S</i>₁</span>, which results in a low contamination risk for groundwater systems. On the contrary, this compound degrades slowly in <span class="inline-formula"><i>S</i>₂</span>, <span class="inline-formula"><i>S</i>₃</span>, <span class="inline-formula"><i>S</i>₄</span>, and <span class="inline-formula"><i>S</i>₅</span>, due to a low adsorption affinity and moderate mobility, which results in a high contamination risk for groundwater systems. Therefore, our results may serve as a reference for evaluating the risks involved in the increasingly wide application of this compound.</p>