Agricultural land uses driven variability of cadmium and lead concentrations, speciation, and plant accumulation: A case study of Tak Province, Thailand

Land-use practices strongly influence the accumulation and distribution of heavy metals in agroecosystems. This study evaluated the effects of land use on cadmium (Cd) and lead (Pb) concentrations, chemical speciation, and plant accumulation across five land-use systems: cassava field, rice paddy field, fruit orchard, maize field, and fallow area. Soil and plant samples were analyzed for total metal concentrations, while metal speciation was determined using sequential extraction (F1–F5). The fallow area contained significantly higher Cd (17.5 mg kg−1) and Pb (4.3 mg kg−1) concentrations than cultivated soils (p < 0.05). However, the concentrations in all land-use systems remained below the current Thai soil quality standards for agricultural land. Cd was mainly associated with the reducible (F3) and residual (F5) fractions, whereas Pb was predominantly found in the oxidizable (F4) and residual (F5) fractions. Principal component analysis revealed that soil physicochemical properties strongly influence heavy metal mobility and bioavailability.