The effect of the different treatments is better highlighted in Fig. 4, showing the average concentration of polyphenols collected throughout the entire test. For soil S1, the highest amounts were reached when either catalytically digested OMW (T1) or concentrated OMW (T4) were introduced in lysimeters. For soil S2, the total amounts of polyphenols leached were generally of the same order of magnitude as the control (T5). This result may be explained by considering that polyphenols coming from natural, agricultural and urban pollution sources can also accumulate in soil and be transported by infiltrating water. Soil loading with polyphenols from OMW in the tested conditions did not lead to further increase of polyphenols in the leachate, except when pre-treated OMW (T1) was applied. However, for both soils, amendments involving diluted and concentrated OMW (treatments T3 and T4, respec- tively) always led to outcoming concentrations of polyphenols that were negligible if compared to the incoming concentration (i.e., less than 0.2% in S1 and less than 0.01% in S2). In all cases, the out- coming concentrations were of the same order of magnitude for all treatments. These results suggest that both OMW application and soil amendment with composted pomace did not lead to significant amounts of polyphenols eventually reaching groundwater, and the catalytical treatment of OMW was unnecessary in view of reducing polyphenols in the leachate.