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Rice plant is efficient in arsenic (As) accumulation due to enhanced soil As release under flooded condition and its effective As uptake. Therefore, rice plant can be used to remove bioavailable As from paddy soil. In this study, the depleting dynamics of soil As with rice growth was mapped two-dimensionally with the zirconium-oxide diffusive gradients in thin films (DGT) technique. Further, the key biochemistry promoting soil As bioavailability was studied to better understand the underlying processes. Results revealed that the average DGT-As encompassing the root zone decreased steeply from 331 in the seedling stage to 136 in the heading & flowering stage and further to 118 μg l−1 at harvest, which was 26% lower than that of the control at 160 μg l−1. During this process, rhizosphere porewater As developed a dynamic profile similar to Fe and dissolved organic carbon, with the diversity of arrA gene peaking at heading & flowering stage. The data support soil As release from microbial reduction of Fe hydroxides fueled by root exudation as carbon source. Arsenic was mainly accumulated in the roots, accounting for up to 95% of total As in rice plants. Removal of rice roots resulted in ~19% lower DGT-As in post-harvest soil compared to without removing the roots. As a result, a sharp decline in As accumulation in rice plants was obtained in the second planting after removing one crop of rice roots. The results highlight that rice, as a paddy-adapted plant, is effective in As uptake in the roots, and thereby removing rice roots efficiently depletes bioavailable As from paddy soils.

Kolleru lake is the largest fresh water lake in the districts of East and West Godavari of Andhra Pradesh, India. Many anthropogenic sources contribute to the heavy metal pollution in the lake and the bioaccumulation of heavy metals in fish helps in assessing the aquatic pollution. Total contents and fractionation of selected heavy metals, viz., Zn, Cu, Cd, Pb, Cr, Ni and Co were measured in sediment sample and three edible fish. The investigation aimed at revealing differences in the accumulation pattern of heavy metals in fish inhabiting sediments characterized by varying metal bioavailability. The metal concentrations were found to be greater than the background concentrations of sediments indicating the anthropogenic origin of metals. Good recovery values were obtained for metal contents in sediments and fish. Large fractions of Zn, Cd and Cu were associated with mobile fraction of sediment and showed greater bioaccumulation in fish whereas Ni and Co were least mobilisable. The results clearly indicate that the fish of Kolleru lake are contaminated with metals and not advisable for human consumption. [Copyright &y& Elsevier]