Use of diffusive gradients in thin films to predict potentially bioavailable selenium in soil

In this study, diffusive gradients in thin films (DGT) were used for determination of anionic selenium (Se) species. First, a laboratory experiment was carried out to investigate ferrihydrite (the anionic sorbent in the DGT) complexation of anionic Se in an aqueous solution. A conditional DGT effective diffusion coefficient (DDGT) for Se was estimated to be 5.0 x 10(-6) and 5.3 x 10(-6) cm(2) s(-1) at pH 5.1 and pH 6.3, respectively. Second, DGT units were placed in pastes of soil that were sampled from a field experiment with mineral Se fertilization at two soil pH levels. Based on the DGT measurements, an effective concentration (C-E) for Se in soil was calculated. A C-E(Se) value significantly higher than the control was estimated at the highest Se dose and the lower pH (5.5). Refinement of the method is needed, but this investigation indicates that the DGT technique can be used to determine potentially bioavailable Se fractions in soil.