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Influence of Humic Acid on Interaction of Ammonium and Potassium Ions on Clay minerals

Pedosphere 2013年第4期23卷 493-502页

作者： ZHANG Wen-Zhao CHEN Xiao-Qin ZHOU Jian-Min LIU Dai-Huan WANG Huo-Yan DU Chang-Wen State Key Laboratory of Soil and Sustainable Agriculture Institute of Soil Science Chinese Academy of Sciences Key Laboratory of Agro-Ecological Processes in Subtropical Region Institue of Subtropical Agriculture Chinese Academy of Sciences

Interaction of ammonium (NH+4) and potassium (K+) is typical in field soils. However, the effects of organic matter on interaction of NH+4 and K+have not been thoroughly investigated. In this study, we examined the changes in major physicochemical properties of three clay minerals (kaolinite, illite, and montmorillonite) after humic acid (HA) coating and evaluated the influences of these changes on the interaction of NH+4 and K+on clay minerals using batch experiments. After HA coating, the cation exchange capacity (CEC) and specific surface area (SSA) of montmorillonite decreased significantly, while little decrease in CEC and SSA occurred in illite and only a slight increase in CEC was found in kaolinite. Humic acid coating significantly increased cation adsorption and preference for NH+4, and this effect was more obvious on clay minerals with a lower CEC. Results of Fourier transform infrared spectrometry analysis showed that HA coating promoted the formation of H-bonds between the adsorbed NH+4 and the organo-mineral complexes. HA coating increased cation fixation capacity on montmorillonite and kaolinite, but the opposite occurred on illite. In addition, HA coating increased the competitiveness of NH+4 on fixation sites. These results showed that HA coating affected both the nature of clay mineral surfaces and the reactions of NH+4 and K+with clay minerals, which might influence the availability of nutrient cations to plants in field soils amended with organic matter.

关键词： adsorption illite kaolinite montmorillonite organo-mineral complex

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Degradation of the fungicide metalaxyl and its non-extractable residue formation in soil clay and silt fractions

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Pedosphere 2021年第4期31卷 549-559页

作者： Roschni KALATHOOR Jens BOTTERWECK Andreas SCHÄFFER Burkhard SCHMIDT Jan SCHWARZBAUER Institute of Geology and Geochemistry of Petroleum and Coal RWTH Aachen UniversityAachen 52062(Germany) Institute for Environmental Research RWTH Aachen UniversityAachen 52062(Germany) School of the Environment Nanjing UniversityNanjing 210023(China)

The proportion of organic matter and mineral composition are important factors determining the formation and type of non-extractable residues(NERs) of pesticides in soil. In this study, we investigated the enantioselectivity in degradation and NER formation of the chiral fungicide metalaxyl in soil particle size fractions(silt and clay). Microbial and extracellular enzyme activities during these processes were monitored in incubation of silt and clay samples isolated from sterilized and non-sterilized soil samples collected from a long-term agricultural field experimental site in Ultuna, Sweden. The temporal influence on the fate of the fungicide was noted by short-term(10-d) and long-term(92-d) incubations. Besides the acquisition of quantitative data with gas chromatography-mass spectrometry(GC/MS), stereoselective analyses were performed with chiral GC/MS. Quantitative results pointed to a higher metabolism rate of the pesticide through microbial activity than through extracellular enzyme activity. This was also confirmed by the enantioselective depletion of R-metalaxyl and the subsequent formation of R-metalaxyl acid in microbially active samples from non-sterilized soil. The silt fraction containing a high amount of organic matter exhibited a significant hydrolyzable proportion of metalaxyl NERs that was releasable under alkaline conditions. On the contrary, the clay fraction showed an enhanced affinity for covalently bound residues. Based on our results, we recommend differentiating between reversibly and irreversibly bound proportions of pesticides in persistence and environmental risk assessment because the reversible fraction contained potentially bioavailable amounts of residues that may be released under natural conditions.

关键词： chiral fungicide enantioselectivity metalaxyl enantiomer non-extractable pesticide residues organo-mineral complex pesticide degradation extracellular enzymes soil particle size fractions

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