First observation of labile arsenic stratification in aluminum sulfate-amended sediments using high resolution Zr-oxide DGT

Arsenic contamination in sediments has received increasing attention because i may be released Lo the water and threaten aquatic organisms. In this study, aluminum sulfate (ALS) was used Lo immobilize As in sediments through dosage-series and Lime-series experiments. Diffusive gradients in thin films (DGT) was used Lo obtain labile As at a vertically 2.0 mm resolution. Our results indicated that a static layer with extremely low labile As concentration (minimally 0.13 mg L-1) with weak variation (<30% RSD) formed within the Lop 12 mm sediment layer al the dosage of 6-12 ALS/As-mobile (kmol mol(-1), As-mobile means the total mobile As in Lop 40 mm sediment) and on days 30-80 atter amendment at the dosage of 9 ALS/As-mobile. The maximum labile As decreased from 1.83 to 0.99 mu g L-1 and from 1.96 to 120 mu g L-1 in the dosage-series (3-12 ALS/As-mobile) and time-series (10-80 days) experiments, respectively, while the depths showing the maximal concentrations moved deeper from 22 to 34 mm and 20 to 32 mm in the sediments. It implied a reduced upward diffusion potential of labile As to the static layer in deeper sediments. Both distribution coefficient for As between sediment solid pool and pore water (K-d) and the adsorption rate constant (k(1)) consistently increased, reflecting that As release from sediment solid became increasingly difficult with the progress of ALS immobilization. The results of this millimeter scale investigation showed that ALS could efficiently immobilize As in sediments under simulated conditions. (C) 2017 Elsevier B.V. All rights reserved.