Kinetic release of arsenic after exogenous inputs into two different types of soil

Abstract

The mobility of arsenic (As) in soil depends on its sorption/desorption processes on soil particles. Plant uptake locally lowers As concentration in soil pore water, which would trigger resupplies of As from soil solid phase. To better understand the fate of As in soil system after its inputs into soil and its subsequent dynamic processes, diffusive gradients in thin films (DGT) technique along with DGT-induced fluxes in soils (DIFS) model were introduced to study the kinetic information of As in soils, including its response time (T_C) and resupply rate constant (k₋₁). To achieve a series of soils with gradient As level, two different types of soils with similar As level (total As in soil JL is 7.4 mg kg⁻¹, while in soil BJ is 6.5 mg kg⁻¹) were collected and amended with exogenous As. Then, DGT deployments were carried out following a period of 90-day soil incubation. The simulated T_C values in non-amended soil JL and soil BJ were 0.036 and 0.001 s⁻¹, respectively. The difference may due to the properties of these two soils, including pH values and contents of adsorption materials, such as Fe and Al compounds. After As inputs into soils, the intrinsic rate of As release from the solid phase to the solution phase in As-amended JL soil was much higher than that in non-amended soil. While for soil BJ, a decreasing trend was observed after As spiking. The redistribution of As may responsible for the different variation trends of As kinetics in these two soils after As spiking. The results indicated that the distribution coefficient of As (K_d) in soil was mainly affected by soil Olsen-P content due to an ubiquitous competition between P and As on soil particles.