Uptake, distribution, and fate of RDX and MNX in dark green bulrush plants

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2009-05

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Abstract

Constructed wetlands are emerging as a promising technology for remediation of water contaminated with low RDX concentrations. A study on the ability of dark green bulrush (Scirpus atrovirens), a wetland plant, to uptake RDX will help to find its utility in constructed wetlands. In this study RDX uptake in actively growing bulrush was evaluated over a sixteen week period at different RDX exposure levels (0.5, 1, 3 mg/l). Plant samples along with influent water, effluent water, and final soil samples were analyzed for RDX, MNX, TNX and DNX. After 16 weeks of exposure and sacrificing 7 of the 9 sets of plants, exposure to RDX was discontinued. The remaining two sets of plants were sacrificed at weeks 19 and 22. RDX concentration in plants substantially decreased during the period of no exposure. About 97% of the RDX concentration in the top third and 75% in bottom and middle thirds of the leaf was lost during the six weeks of cessation to RDX exposure. RDX uptake in mature bulrush was also evaluated over a six week period at 1 mg/l exposure concentration. RDX was detected at higher concentrations in the top third of the leaf when compared to middle and bottom thirds in actively growing as well as in mature bulrush. MNX was detected in 99% of plant and soil samples. DNX and TNX were detected in few bottom thirds of the leaf and root portions of the bulrush in very low concentrations (0.003 to 0.03 mg/kg), but were very rarely detected in other samples. MNX uptake in mature bulrush was also evaluated over a five week period at 0.5 mg/l exposure concentration. Unaccounted MNX in the treatment systems of bulrush exposed to 0.5 mg/l MNX was around 59% compared to unaccounted RDX of 19, 23 and 38% respectively for 0.5, 1, 3 mg/l RDX exposure treatment systems. No bleaching or necrosis was observed during the course of the experiment in any of the plants. The results are suggesting that RDX exposure up to 3.0 mg/l does not have any adverse effects on bulrush. RDX accumulation in actively growing bulrush increased with time but in mature bulrush RDX accumulation remained more or less constant.

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