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TECHNICAL REPORTS

Organic Compounds in the Environment

Contribution of Hydrolysis in the Abiotic Attenuation of RDX and HMX in Coastal Waters

Biotechnology Research Inst., National Research Council of Canada, 6100 Royalmount Avenue, Montréal, Québec, Canada H4P 2R2

^* Corresponding author (jalal.hawari{at}cnrc-nrc.gc.ca).

Received for publication August 23, 2007. Sinking of military ships, dumping of munitions during the two World Wars, and military training have resulted in the undersea deposition of numerous unexploded ordnances (UXOs). Leaching of energetic compounds such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) from these UXOs may cause adverse ecological effects so that the long-term fate of these chemicals in the sea should be known. The present study assesses the contribution of alkaline hydrolysis into the natural attenuation of RDX and HMX in coastal waters. Alkaline hydrolysis rates were shown to be unaffected by the presence of sodium chloride, the most common component in marine waters. Kinetic parameters (E_a, ln A, k₂) quantified for the alkaline hydrolysis of RDX and HMX in deionized water (30–50°C, pH 10–12) agreed relatively well with abiotic degradation rates determined in sterilized natural coastal waters (50 and 60°C, variable salinity) even if the latter were generally slightly faster than the former. Furthermore, similar products (HCHO, NO₂^–, O₂NNHCH₂NHCHO) were obtained on alkaline hydrolysis in deionized water and abiotic degradation in coastal waters. These two findings suggested that degradation of nitramines in sterilized natural coastal waters, away from light, was mainly governed by alkaline hydrolysis. Kinetic calculations using the present parameters showed that alkaline hydrolysis of RDX and HMX in marine waters at 10°C would respectively take 112 ± 10 and 2408 ± 217 yr to be completed (99.0%). We concluded that under natural conditions hydrolysis should not contribute significantly to the natural attenuation of HMX in coastal waters whereas it could play an active role in the natural attenuation of RDX.

Abbreviations: DW, deionized water • E_a, activation energy • k₁, pseudo-first order rate constant • k₂, second order rate constant • ln A, Arrhenius factor • UXOs, unexploded ordnances