Proton binding properties of humic substances originating from natural and contaminated materials

Humic substances (HS) are ubiquitous organic constituents in soil and water and can strongly adsorb metal contaminants in natural and waste environments. Therefore, understanding and modeling contaminant-HS interactions is a key issue in environmental risk assessment. Current binding models for HS, such as the nonideal competitive adsorption (NICA)-Donnan model, are developed and calibrated against natural organic matter from soils and surface waters. The aim of this study is to analyze the proton binding properties of humic and fulvic acid samples originating from secondary materials, waste materials and natural samples in order to assess whether the charge development of these HS can be described with generic NICA-Donnan parameters. New proton binding parameters are presented for HS isolated from several natural and contaminated (waste) materials. These parameters are shown to be similar to those of HS originating from natural environments, suggesting that the NICA-Donnan model and generic binding parameters are adequate to describe proton binding to HS in both natural and contaminated materials. These findings widen the range of environments to which the NICA-Donnan model can be applied and justify its use in geochemical speciation modeling of metal mobility in contaminated (waste) material