Studies on arsenic transport across and down some soils of West Bengal

The vertical and horizontal transport of aqueous arsenic across and down three surface soil samples was studied with the help of a horizontal cell and a double-chambered vertical column. The data on transport of arsenic across the soil column were fitted to formulations, based on irreversible thermodynamics, to yield the parameters, such as reflection coefficient (σ), mechanical filtration capacity (Lp), solute permeability (ω), as well as hydrodynamic frictional coefficients for osmotic flow of aqueous arsenic through the given soils. These parameters provided useful information in regard to retention/release pattern of arsenic in course of passage through the given soils. The study with the vertical soil column led to findings, relating to Darcy's saturated hydraulic conductivity, arsenic accumulation and relative hold-up of arsenic by the given permeating media, as revealed by the breakthrough curves. The different times of dilution of aqueous arsenic passing through the soils under study, along with the different values of primarily the reflection coefficient (σ), suggested the varying degrees of accumulation of arsenic in the experimental soils. The approximately sigmoid shape of the breakthrough curves for aqueous arsenic solution in the given soils was noted with a shift of the breakthrough curve to the left of the inflexion point (at Pv = 1.0). The latter tended to suggest substantial arsenic retention by these soils. The findings from this study are expected to elucidate better the deposition and concentration of arsenic across and down a soil profile, subjected to irrigation with arsenic-contaminated water. An attempt has been made to relate such arsenic retention behaviour of the present soils to the relevant properties of the given soils.