Impacts of salinity level and flood irrigation on Cd mobility through a Cd-contaminated soil, Thailand: experimental and modeling techniques

Abstract

The objective of this research was to investigate the effects of salinity levels and pore water velocity (PV) on the sorption, fate, and transport of Cd through contaminated soil in low-lying areas along Mae Tao Creek, Tak Province, Thailand. Soil samples collected from a depth of 15 cm from the rice field were air-dried, ground, and sieved through a 2-mm sieve prior to the experiments. Batch sorption/desorption experiments were conducted under three salinity levels, 1, 10, and 100 mM, using CaCl2 as salt. The six columns for the Cd transport experiments were performed with low and high pore water velocities (2 and 9 cm/h) and salinity levels of 1, 10, and 100 mM. Effects on Cd rate-limited sorption and transport behavior were evaluated using the sorption isotherms, PHREEQC geochemical modeling, and mathematical model, HYDRUS-1D. For the batch experiments, the Freundlich isotherm was found to be the best sorption isotherm to explain the Cd sorption (R2 > 0.93, p value < 0.05). The Langmuir two-site model (TSM) well explained the breakthrough curves of the column experiments with Langmuir sorption coefficient (KL) ranging from 0.09 to 4.03 l/g. Salinity levels appeared to significantly increase the equilibrium fraction site (f) and first-order rate constant (α) on Cd sorption and transport over the salinity levels of 10–100 mM due to the competitive effect and the dominant species of Cd. Solute transport parameters in the TSM can be used as an efficient decision support tool to predict Cd movement through contaminated sandy loam soils under a flood irrigation area.