Roles of Soil Organic Matter and Humic Substance Structure in Cu and Pb Adsorption in Histosols

Histosols have a high organic matter content and therefore a high variability of structures and chemical functional groups with adsorptive capacity. This study aimed to select the most appropriate models to describe the sorption phenomena of Cu and Pb in Histosols, identify the types of bonds between these metals and soil samples, and assess the influence of soil attributes and soil humic substance structures on these bonds. The Freundlich and Langmuir models were selected based on the values of the corrected Akaike information criterion and variation of Akaike information criterion as the best models for describing Cu and Pb sorption in Histosols. The values of the adsorption coefficients provided by the models indicated that Pb has higher affinity with the studied soil relative to Cu. However, Cu adsorption to soil occurs specifically and Pb is adsorbed nonspecifically. In general, the contents of N and fulvic acids were the factors that most influenced Pb sorption. Pb has a higher association with more aliphatic fulvic character structures, while Cu has a higher association with soil humic character structures. Therefore, compared to Cu, Pb in the studied Histosol has greater bioavailability potential and, consequently, greater risks of contamination and entering the food chain.