Institute of Environment and Plant Protection, Chinese Academy of Tropical Agricultural Sciences, Haikou, 571101, PR China; National Agricultural Experimental Station for Agricultural Environment, Tropical Agro-ecosystem, National Observation and Research Station, Danzhou, 571737, PR China.
College of Environmental Science and Engineering, China West Normal University, Nanchong, 637009, PR China.
Environ Pollut. 2022 Oct 15;311:119949. doi: 10.1016/j.envpol.2022.119949. Epub 2022 Aug 12.
Complexation of dissolved organic matter (DOM) plays a crucial role in regulating the fate and risk of agrochemicals. Here, taking a toxic herbicide MCPA (4-chloro-2- methylphenoxyacetic acid) as the target, the effect of land conversion on complexation behavior of DOM to agrochemicals was investigated in paddy soil. Furthermore, the mechanisms were explored in a new perspective of DOM chemodiversity. Soil DOMs were selected from four long-term cropping systems, including paddy field (PF), vegetable field (VF), rice-vegetable rotation (RV) and abandoned land (AL). The results showed that the DOMs in PF and AL were rich in hydrophilic substances (e.g., carbohydrates or protein-like molecules) with low aromaticity. However, after converting PF to VF and RV, abundant aromatic macromolecules and aliphatic alkanes were observed in DOM. Due to those changes in DOM chemodiversity, the binding site and capability of DOM were highest in VF and RV, and were positively correlated with DOM aromaticity, MW, humus and polar groups (e.g., amino). This was because the complexation of "DOM-MCPA" was static binding via ligand exchange and H-bonding among polar groups and hydrophobic interaction among aromatic skeletons. The EEM-PARAFAC confirmed that microbial humic-like substances dominated the complexation of DOM rather than terrestrial humic-like and tryptophan-like matters. The 2D-COS analysis further revealed that the complexation of DOM preferentially occurred in amino, polysaccharide C-O and aliphatic C-H for PF and AL, but in aromatic C=C, amide C=N for RV and VF. In summary, these findings provide molecular insight into the effect of land conversion on DOM complexation activity, which highlight the importance of DOM chemodiversity. These results will contribute to the risk assessments of agrochemicals in paddy soil.
溶解有机质（DOM）的络合作用对于调控农用化学品的归宿和风险起着至关重要的作用。在这里，以有毒除草剂 MCPA（4-氯-2-甲基苯氧乙酸）为目标物，研究了土地利用方式转变对稻田土壤中 DOM 与农用化学品络合行为的影响。此外，还从 DOM 化学多样性的新视角探讨了其机制。从四个长期耕作系统中选择了土壤 DOM，包括稻田（PF）、菜地（VF）、稻菜轮作（RV）和撂荒地（AL）。结果表明，PF 和 AL 中的 DOM 富含亲水性物质（如碳水化合物或类蛋白分子），芳香度较低。然而，将 PF 转换为 VF 和 RV 后，DOM 中出现了丰富的芳香大分子和脂肪烷烃。由于 DOM 化学多样性的这些变化，VF 和 RV 中 DOM 的结合位点和能力最高，与 DOM 的芳香度、MW、腐殖质和极性基团（如氨基）呈正相关。这是因为“DOM-MCPA”的络合是通过极性基团之间的配体交换和氢键以及芳香骨架之间的疏水相互作用进行的静态结合。EEM-PARAFAC 证实，微生物腐殖质样物质主导了 DOM 的络合作用，而不是陆地腐殖质样和色氨酸样物质。2D-COS 分析进一步表明，对于 PF 和 AL，DOM 的络合优先发生在氨基、多糖 C-O 和脂肪族 C-H 上，而对于 RV 和 VF，则优先发生在芳香族 C=C 和酰胺 C=N 上。综上所述，这些发现为土地利用方式转变对 DOM 络合活性的影响提供了分子层面的认识，强调了 DOM 化学多样性的重要性。这些结果将有助于评估农用化学品在稻田土壤中的风险。
