In situ, high resolution ZrO-Chelex DGT for the investigation of iron-coupled inactivation of arsenic in sediments by macrozoobenthos bioturbation and hydrodynamic interactions

Abstract

The influence of chironomid larvae and hydrodynamics on the bioavailable arsenic (As) in sediments under different conditions was comprehensively investigated through water tank experiments spanning 132days. The high-resolution technique of revealing diffusive gradients in thin films (DGT) with ZrO-Chelex resin was employed in this study; this was done to simultaneously obtain concentrations of labile As and Fe in the profile at millimeter resolution. Bioturbation by larvae may significantly decrease the bioavailable As and Fe concentrations under different hydrodynamic intensities during the first two months of larval burrowing; the greatest difference between the bioavailable As concentration with and without the addition of larvae was seen on the 56th day, with around 49%, 47%, 73% and 67% reduction of As in the profile under static water, 0.3ms−1, 0.5ms−1 and 1.0ms−1, respectively. However, these effects were diminished after the 56th day due to the eclosion of the chironomid larvae. The hydrodynamic conditions appeared to not have any significant effect on the labile concentration of As or Fe until after eclosion. The changing distributions of labile As and Fe were consistent with the dissolved oxygen concentrations in the profile under different conditions. Labile As showed the significantly correlation coefficients with labile Fe by a stepwise multiple linear regression under different experimental conditions in this study. We conclude that the decreases in bioavailable As are directly related to conversions between Fe2+ and Fe3.