Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS), CSIC, Avenida Reina Mercedes 10, P.O. Box 1052, 41080 Sevilla, Spain.
Department of Environmental Sciences, The Connecticut Agricultural Experiment Station, 123 Huntington St., P.O. Box 1106, New Haven, CT 06504-1106, United States.
Sci Total Environ. 2016 Jan 15;541:776-783. doi: 10.1016/j.scitotenv.2015.09.097. Epub 2015 Oct 2.
A large number of pesticides are chiral and reach the environment as mixtures of optical isomers or enantiomers. Agricultural practices can affect differently the environmental fate of the individual enantiomers. We investigated how amending an agricultural soil with composted olive-mill waste (OMWc) or its biochar (BC) at 2% (w:w) affected the sorption, degradation, and leaching of each of the two enantiomers of the chiral fungicide metalaxyl. Sorption of metalaxyl enantiomers was higher on BC (Kd ≈ 145 L kg(-1)) than on OMWc (Kd ≈ 22 L kg(-1)) and was not enantioselective in either case, and followed the order BC-amended>OMWc-amended>unamended soil. Both enantiomers showed greater resistance to desorption from BC-amended soil compared to unamended and OMWc-amended soil. Dissipation studies revealed that the degradation of metalaxyl was more enantioselective (R>S) in unamended and OMWc-amended soil than in BC-amended soil. The leaching of both S- and R-metalaxyl from soil columns was almost completely suppressed after amending the soil with BC and metalaxyl residues remaining in the soil columns were more racemic than those in soil column leachates. Our findings show that addition of BC affected the final enantioselective behavior of metalaxyl in soil indirectly by reducing its bioavailability through sorption, and to a greater extent than OMWc. BC showed high sorption capacity to remove metalaxyl enantiomers from water, immobilize metalaxyl enantiomers in soil, and mitigate the groundwater contamination problems particularly associated with the high leaching potential of the more persistent enantiomer.
大量的农药具有手性，以对映异构体或光学异构体混合物的形式进入环境。农业实践可以影响各个对映体在环境中的命运。我们研究了在 2%（w/w）的条件下，用堆肥橄榄渣（OMWc）或其生物炭（BC）改良农业土壤如何影响手性杀菌剂金属axyl 的两种对映体的吸附、降解和淋溶。金属 axyl 对映体在 BC（Kd≈145 L kg(-1))上的吸附高于 OMWc（Kd≈22 L kg(-1))，且两种情况下均无手性选择性，且顺序为 BC 改良>OMWc 改良>未改良土壤。与未改良和 OMWc 改良土壤相比，两种对映体从 BC 改良土壤中解吸的抵抗力更大。耗散研究表明，金属 axyl 在未改良和 OMWc 改良土壤中的降解更具对映体选择性（R>S），而在 BC 改良土壤中则较低。在土壤中添加 BC 后，两种 S-和 R-金属 axyl 从土壤柱中的淋溶几乎完全被抑制，并且留在土壤柱中的金属 axyl 残留比土壤柱淋出液中的更接近外消旋。我们的研究结果表明，BC 的添加通过吸附减少了金属 axyl 的生物利用度，从而间接影响了金属 axyl 在土壤中的最终对映体选择性行为，其影响程度大于 OMWc。BC 对金属 axyl 对映体具有高吸附能力，可以从水中去除，将金属 axyl 对映体固定在土壤中，并减轻与更持久对映体高淋溶潜力相关的地下水污染问题。
