Degradation and Transport of the Chiral Herbicide S-Metolachlor at the Catchment Scale: Combining Observation Scales and Analytical Approaches,Environmental Science & Technology

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Degradation and Transport of the Chiral Herbicide S-Metolachlor at the Catchment Scale: Combining Observation Scales and Analytical Approaches
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2017-11-10 00:00:00 , DOI: 10.1021/acs.est.7b02297
Lefrancq Marie _{1,

2} , Payraudeau Sylvain ₁ , Guyot Benoit ₁ , Millet Maurice ₃ , Imfeld Gwenaël ₁

Affiliation

Evaluating pesticide degradation and transport in the soil-surface water continuum remains challenging at the catchment scale. Here we investigated the dissipation of the chiral herbicide S-metolachlor (SM) in soil in relation to its transport in runoff. Analyses of SM, transformation products (TPs, i.e., MESA and MOXA), and enantiomers were combined to determine SM degradation at plot and catchment scales. Assisted by modeling, we found that the main dissipation pathways of SM at the plot scale were degradation (71%), volatilization (5%), leaching (8%) and runoff (3%), while 13% of SM persisted in topsoil. This highlights the relevance of degradation processes. TPs could trace the different discharge contributions: MOXA prevailed in runoff water, whereas MESA was associated with slower flowpaths. At the catchment outlet, 11% of SM applied was exported in dissolved or particulate phases or as TPs (in SM mass equivalent). A single event 1 week after application exported 96% of SM, which underlined the potential importance of severe rainfall on seasonal SM export. Enantioselective degradation enriched SM in the R-enantiomer over longer periods and may be associated with slower flowpaths. Altogether, combining observation scales and analytical approaches enabled to quantify SM degradation and to identify how degradation controls SM export at the catchment scale.

中文翻译：

流域尺度上手性除草剂S-甲草胺的降解和运输：结合观察尺度和分析方法

在集水区范围内，评估农药在土壤-地表水连续体中的降解和迁移仍然具有挑战性。在这里我们研究了手性除草剂S的消散土壤中的甲草胺（SM）与其在径流中的运输有关。对SM，转化产物（TPs，即MESA和MOXA）和对映异构体进行分析，以确定地块和集水区规模的SM降解情况。在建模的辅助下，我们发现样地尺度上SM的主要消散途径为降解（71％），挥发（5％），淋失（8％）和径流（3％），而13％的SM持续存在于表土中。。这突出了降解过程的相关性。TP可以追踪不同的排放贡献：径流水中普遍使用MOXA，而MESA与较慢的流路相关。在集水区出口处，所施用的11％的SM以溶解相或颗粒相或以TP形式（以SM质量当量计）出口。申请后1周的一次活动导出了96％的SM，这突显了强降雨对季节性SM出口的潜在重要性。对映选择性降解富集SM中的SM。R-对映体在更长的时期内可能与较慢的流动路径有关。总而言之，将观察量表和分析方法结合起来可以量化SM退化并确定退化如何控制流域尺度上的SM出口。

更新日期：2017-11-11

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