Digestate-Derived Compost Modulates the Retention/Release Process of Organic Xenobiotics in Amended Soil

This study examined the effects of 2, 4 and 8% digestate-derived compost (DCP) on the retention/release of the fungicide penconazole (PEN), the herbicide S-metolachlor (S-MET) and the endocrine disruptor bisphenol A (BPA) in two agricultural soils sampled in Valenzano (SOV) and Trani (SOT), in Sothern Italy. DCP alone showed a conspicuous adsorption of the three xenobiotics, followed by their slow and scarce release. Sorption isotherm data of the compounds on unamended and DCP-amended soils were well described by the Freundlich model. Compared to unamended soil, the addition of the highest dose (8%) DCP to SOV increased the distribution coefficient, Kd, values of PEN, S-MET and BPA by 281%, 192% and 176%, respectively, while for SOT, the increases were 972%, 786% and 563%, respectively. Desorption of PEN and S-MET from all treatments was slow and partial (hysteresis), and only slightly reduced or unaffected by the addition of DCP, whereas BPA was almost entirely undesorbed in all treatments. Highly significant correlations between the adsorption coefficients of the three compounds in all soil treatments and the corresponding organic C contents confirm the prominent role of native and anthropogenic OM in the adsorption of contaminants and, consequently, in the control of their transfer into natural waters and/or entry in crop plants.