RDX degradation by chemical oxidation using calcium peroxide in bench scale sludge systems.

The ability of calcium peroxide (CaO2) to degrade hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in contaminated soil slurries using CaO2-based modified Fenton oxidation was investigated. Results showed that increasing the CaO2 dose increased degradation rates of RDX and pH. RDX concentrations decreased to below detection after 18 h with 2 M and 2.5 M CaO2, after 30 h with 1.5 M CaO2, after 54 h with 1 M CaO2, but 0.1 M CaO2 achieved no significant RDX removal. Increasing the soil organic matter content decreased the rate and extent of RDX degradation. RDX degradation products 4-nitro-2,4-diazabutanal (NDAB) and methylenedinitramine (MEDINA) were quantified, and the greater accumulation of NDAB than MEDINA suggests denitration of RDX was the most likely initial degradation step. Isotopic ratios for nitrogen and oxygen associated with RDX oxidation are also consistent with either nitrification of NH4+ from soil or precipitation. Existing technologies merely only extract energetics from soils for treatment ex situ, whereas the approach introduced herein destroys RDX in situ with a one-step application.

A Conceptual Model of Fate and Transport Processes for RDX Deposited to Surface Soils of North American Active Demolition Sites.

The use of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) as an energetic material (EM) in ammunition constituents such as detonators, primers, mines, and rocket boosters and in plastic explosives has led to an international warning on possible soil, surface water, and groundwater contamination on military training sites. In Canada, the demolition sites of range training areas are known to be the second most contaminated sites by EM residues in terms of their concentrations in soil after anti-tank ranges. This research proposes a conceptual model of the presence of RDX at the field scale at demolition sites according to previous soil and water characterization studies. This model illustrates the origin of RDX contamination, the main RDX transport pathways and processes, and the main threatened receptors. This conceptual model is of importance to visualize and understand RDX's environmental fate and behavior and to ultimately enable the production of a detailed quantitative model that can help to manage those RDX-contaminated sites.

Sr-90 soil to plant transfer factor reduction using calcium and polymer soil amendments.

Introducing calcium into soils can inhibit Sr-90 uptake by plants. To test the efficacy of calcium amendments on the inhibition of Sr-90 uptake by edible plants, a number of different calcium applications, including calcium nitrate, calcium thiosulfate and a mixture of both liquid solutions, were used in this study. Pea plants (Pisum sativum 'Sabre') grown in Sr-90 contaminated soil from seeds to maturity were watered with these calcium solutions. Two different polymers, one inert and one nutrient enriched, were incorporated into the contaminated soil where pea seeds were sowed to ascertain a continuous supply of calcium and essential nutrients. Results show that the heterogeneity of Sr-90 distribution in soil translated to disparate Sr-90 contents in plant tissues. However, on average, irrigation with calcium solutions in conjunction with the usage of polymers consistently yielded a reduction in Sr-90 uptake by the plants. The lowest soil-to-plant transfer factor (TF) values were measured in the edible pea part of the plant, followed by the flowers, roots, stems, pea shells and then leaves. TF values for pea shells were between 4.9 and 20.9, and between 0.3 and 2.8 for the peas. Results do not allow the identification of one particular chemical solution that would systematically be the best choice to minimize Sr-90 uptake.

Assessing effects of legacy nuclear waste on plants: Sensitive fern (Onoclea sensibilis) gametophyte viability at the Chalk River site.

We evaluated the effects of chronic exposure to environmental radiological contamination on the reproductive fitness of sensitive fern (Onoclea sensibilis) by quantifying viability in haploid gametophytes of spores collected from ferns from background and contaminated areas of the Chalk River site. Dose rates measured in situ at field sites ranged from 60 to 849 µGy h-1, with effects possible at the more contaminated sites (greater than 400 µGy h-1). Fern spores were also irradiated from 1 to 1000 Gy to develop dose-response curves. We found no effects on gametophyte viability at the most contaminated areas of the Chalk River site, where we estimated growing season doses of 0.3-3.7 Gy. Dose-response curves show evidence of hormesis, with an increase in gametophyte viability up to 10 Gy, followed by a rapid decline to no viable gametophytes at doses of 1000 Gy. The sensitive fern is not a radiosensitive plant species, but effects do occur within the normal range (10-1000 Gy) of most plant species, making it useful as a sentinel species from a community perspective. Sensitive fern spore germination is high and stable over field dose ranges, with effects primarily on gametophyte viability. This method shows promise as an effects monitoring tool for sites with radiological contamination.

Effect of energetic materials wettability on their outdoor effective elution rate.

Energetic materials (EM) contained in military ammunitions have been found in the surface soil and water of training areas and may potentially represent a threat to human health and the environment. EM wettability is an essential physical parameter to characterize because it controls EM dissolution rate. This paper was conducted to determine the wettability of conventional and new EM formulations used in military ammunition. Wettability was estimated in the laboratory via contact angle measurements of water droplets on different EM surfaces. Results show that 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitro-1,3,5-triazinane (RDX), Octol and energetic thermoplastic elastomer (ETPE) 1000 are hydrophilic while Composition B, XRT, GIM, CX-85, ETPE 2000, and C4 are hydrophobic whereas HELOVA gun propellant has a mixed wettability oscillating between hydrophilic and hydrophobic. The present study demonstrates that wettability of EM formulation is generally controlled by their matrix constituents. Results indicate that hydrophobic formulations have a much slower outdoor environmental effective elution rate than hydrophilic ones, with the exception of the hydrophobic C4 formulation whose elution rate is extremely high. The addition of hydrophobic components into EM formulations is recommended to diminish the environmental impact on water, as it has already been done with XRT, GIM and CX-85 formulations.