| Abstrakt: |
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 KFads 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. [ABSTRACT FROM AUTHOR] |
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