Arsenic Interactions in Agricultural Soils from Punjab, India: Insights from Triple Layer Surface Complexation Modeling

This study combines batch adsorption experiments and surface complexation modelling to investigate the interactions of arsenate [As(V)] and arsenite [As(III)] with agricultural soils from an arsenic (As) contaminated district of Punjab, India. Batch adsorption studies were conducted to investigate the impact of contact time, As loadings, ionic strength and solution pH on As retention under conditions representative of the regional environment. As adsorption was significantly higher in surface soil layers than in bottom layers, largely due to variations in surface area, organic matter content, pH, and mineralogical components. Experimental data were interpreted using a generalized composite triple layer model (GC-TLM), representing the average surface reactivity of the natural soil assemblage. Modelling results indicate that As(V) predominantly forms inner-sphere surface complexes, whereas As(III) forms both inner and outer-sphere complexes. The model successfully reproduced adsorption isotherms and pH-edge behaviour within reasonable RMSE, demonstrating its applicability to natural soils. These findings improve the mechanistic understanding of As-soil interactions and provide a basis for predicting As mobility in agricultural soils of Punjab.