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The present study evaluated uranium (U) removal ability and tolerance to low level nuclear waste (LLNW) of an aquatic weed Hydrilla verticillata . Plants were screened for growth in 10%–50% waste treatments up to 3 d. Treatments of 20% and 50% waste imposed increasing toxicity with duration assessed in terms of change in fresh weight and in the levels of photosynthetic pigments and thiobarbituric acid-reactive substances. U concentration, however, did not show a progressive increase and was about 42 μg g −1 dw from 20% to 50% waste at 3 d. This suggested that a saturation stage was reached with respect to U removal due to increasing toxicity. However, in another experiment with 10% waste and 10% waste+10 ppm U treatments, plants showed an increase in U concentration with the maximum level approaching 426 μg g −1 dw at 3 d without showing any toxicity as compared to that at 20% and 50% waste treatments. Hence, plants possessed significant potential to take up U and toxicity of LLNW limited their U removal ability. This implies that the use of Hydrilla plants for U removal from LLNW is feasible at low concentrations and would require repeated harvesting at short intervals. [ABSTRACT FROM AUTHOR]

A field experiment was conducted in a combinatorial approach to evaluate the performance of five aquatic plants, singly and in all possible combinations of two plants, for As removal from 4 L of 2500 μg L −1 As in 30 days. Under As stress, Hydrilla showed an increase in growth rate (19%) in comparison to control, while other plants demonstrated a decline. Among different combinations, Ceratophyllum + Lemna , Hydrilla + Ceratophyllum and Hydrilla + Wolffia showed higher growth in As (92%, 43%, and 33%, respectively) than under control conditions. Total As removal (μg) in 30 days was found to be the maximum for Ceratophyllum + Lemna (4365) followed by Hydrilla + Ceratophyllum (3326) and Hydrilla + Wolffia (1896). In all combinations of plants, Hydrilla always contributed more than 50%. The study advocates the use of Hydrilla / Ceratophyllum as one plant of choice to be used in combination. It also proposes to screen for different combinations of two of more plants for better application of phytoremediation technology in field. [ABSTRACT FROM AUTHOR]

In the present study, Hydrilla verticillata plants were exposed to arsenate (AsV; 50μM) and arsenite (AsIII; 5μM) under variable S supply: deficient (2μM S, –S), normal (1mM S, +S) and excess (2mM S, +HS). Arsenic accumulation (μgg−1 dw) in +HS plants was about 2-fold higher upon exposure to both AsV (30) and AsIII (50) than that observed in +S (12 & 24) and –S (14 & 26) plants. Despite lower As accumulation, –S plants experienced the maximum oxidative stress owing to an inadequate response of enzymatic and molecular antioxidants and significant decline in total thiols and the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG). By contrast +HS plants had significant increase in total thiols and an improved redox status, did not demonstrate any negative impact to antioxidants except catalase and hence experienced the least increase in oxidative stress parameters. In conclusion, an increase in S supply to plants may improve their accumulation capacity for As through enhanced tolerance caused by a positive effect on thiol metabolism and antioxidant status of the plants. [Copyright &y& Elsevier]