Purpose

The decline in organic matter content in many agricultural soils results in a dramatic decrease in their ability to retain xenobiotics. Due to its carbon-rich nature and sorptive behaviour, digestate used as soil amendment can counteract this trend. This study investigated the sorption efficiency of the herbicide oxyfluorfen and the fungicide boscalid by a digestate from olive pomace only, and by a loamy calcareous agricultural soil before and after its amendment with 2 and 5% (w/w) digestate.

Methods

To investigate the surface micromorphology and the functional groups of the digestate, scanning electron microscopy (SEM-EDX) and Fourier-transform infrared (FTIR) spectroscopy were employed, respectively. Adsorption kinetics and adsorption/desorption isotherms of the compounds on the digestate and the soil were performed. Adsorption data were described using the Henry, Freundlich, Langmuir and Temkin equations.

Results

Both oxyfluorfen and boscalid reached the steady state on both substrates in approximately 2 h according to a pseudo-second order model, thus denoting a prevalent chemisorptive interaction. The Freundlich model was generally the best fit for both molecules on any substrate. The K_Fads values for oxyfluorfen on the digestate, soil, soil + 2% digestate, and soil + 5% digestate were, respectively, 7158, 19, 60 and 170 L kg⁻¹, while for boscalid, in the same order, they were 3700, 11, 37 and 31 L kg⁻¹, at a temperature of 20 °C. The desorption of both compounds from the non-amended and amended soil and, especially, from the digestate was quite slow and incomplete, indicating the occurrence of a hysteretic process. Highly significant correlations were found for both molecules between the adsorption and desorption parameters of all adsorbents and their organic carbon content.

Conclusion

This study confirms the prominent role of organic matter in the retention/release of pesticides in soil. It is expected that the addition of digestate to soil can reduce the risk of transport of toxic compounds in natural waters and/or limit their uptake in edible plant organs.

中文翻译：

---

橄榄果渣消化物和消化物改良土壤中杀虫剂乙氧氟草醚和啶酰菌胺的吸附和释放

目的

许多农业土壤中有机质含量的下降导致其保留外源物质的能力急剧下降。由于其富含碳的性质和吸附行为，沼渣用作土壤改良剂可以抵消这种趋势。本研究调查了仅来自橄榄果渣的消化物以及用 2% 和 5%（w/w）消化物改良前后的钙质肥沃农业土壤对除草剂乙氧氟草醚和杀菌剂啶酰菌胺的吸附效率。

方法

为了研究消化物的表面微形态和官能团，分别采用扫描电子显微镜（SEM-EDX）和傅里叶变换红外（FTIR）光谱。进行了化合物在消化物和土壤上的吸附动力学和吸附/解吸等温线。使用 Henry、Freundlich、Langmuir 和 Temkin 方程描述吸附数据。

结果

根据伪二阶模型，乙氧氟草醚和啶酰菌胺在两种底物上均在大约 2 小时内达到稳态，从而表明存在普遍的化学吸附相互作用。 Freundlich 模型通常最适合任何基质上的两种分子。乙氧氟草醚在消化物、土壤、土壤 + 2% 消化物和土壤 + 5% 消化物上的K _Fads值分别为 7158、19、60 和 170 L kg ^-1，而对于啶酰菌胺，按相同顺序，它们为温度为20℃时，分别为3700、11、37和31L kg ^-1 。两种化合物从未改良和改良土壤中的解吸，特别是从消化物中的解吸相当缓慢且不完全，表明发生了滞后过程。对于所有吸附剂的吸附和解吸参数与其有机碳含量之间的这两种分子都发现了高度显着的相关性。

结论

这项研究证实了有机物在土壤中农药保留/释放中的重要作用。预计向土壤中添加消化物可以降低有毒化合物在天然水中运输的风险和/或限制其在可食用植物器官中的吸收。