Background

Pelargonic acid is a non-selective herbicide derived from natural sources with a range of potential applications in areas where synthetic herbicides may be less acceptable. One such use area is weed control on railway tracks. To assess the potential leaching of pelargonic acid to groundwater for this specific use, we conducted degradation and sorption studies with soils from railway tracks and, for comparison, with a range of topsoils.

Results

Degradation of pelargonic acid was very rapid in subsoils from railway tracks with half-lives (DT₅₀) of < 1 day (geom. mean DT₅₀, 5.8 h), and even faster in the selected agricultural topsoils (1.5 h). The starting concentration had a strong influence with much slower degradation at higher spike levels. Adsorption to the railway soils (alkaline soils with low organic matter content) was expectedly weak (Freundlich adsorption coefficients K_F of 0.06–0.31 mL/g) and clearly stronger in the topsoils (0.2–40 mL/g). Organic carbon normalized adsorption coefficients (K_Foc) ranged from 11 to 371 mL/g (all soils) and were pH dependent, consistent with the behaviour of weak acids. Computer modelling using the software PELMO and a set of scenarios for herbicide use on railway tracks developed for the authorisation in Germany yielded predicted environmental concentrations in groundwater of < 0.001 µg/L when parameterised with the adsorption and degradation endpoints from subsoils.

Conclusions

The leaching potential of pelargonic acid may be considered low even in application scenarios with sandy soils with low organic matter content such as those found below railway tracks.

中文翻译：

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与一系列表土相比，铁路轨道下方的底土中除草剂壬酸的降解和吸附

背景

壬酸是一种源自天然来源的非选择性除草剂，在合成除草剂不太可接受的地区具有一系列潜在应用。其中一个应用领域是铁轨上的杂草控制。为了评估壬酸在这种特定用途下浸入地下水的可能性，我们对铁路轨道的土壤进行了降解和吸附研究，并与一系列表土进行了比较。

结果

铁路轨道下土中壬酸的降解速度非常快，半衰期 (DT ₅₀ ) < 1 天（几何平均 DT ₅₀ , 5.8 小时），在选定的农业表土中降解速度更快（1.5 小时）。起始浓度有很大的影响，在较高的加标水平下降解速度要慢得多。预计铁路土壤（有机质含量低的碱性土壤）的吸附较弱（Freundlich 吸附系数 K _F为 0.06–0.31 mL/g），而表土的吸附明显较强（0.2–40 mL/g）。有机碳归一化吸附系数 (K _Foc ) 范围为 11 至 371 mL/g（所有土壤），并且与 pH 值相关，与弱酸的行为一致。使用软件 PELMO 和为德国授权而开发的一组铁轨使用除草剂场景进行计算机建模，当使用底土的吸附和降解终点进行参数化时，预测地下水中的环境浓度将低于 0.001 µg/L。

结论

即使在有机质含量低的沙质土壤（例如铁轨下方的沙质土壤）的应用场景中，壬酸的浸出潜力也可能被认为较低。