A time series investigation of the stability of nitramine and nitroaromatic explosives in surface water samples at ambient temperature

We investigated the fate of nitramine and nitroaromatic explosives compounds in surface water to determine how surface water biogeochemistry affects the stability of explosives compounds. Five river water samples and 18.2 MX deionized water were spiked with 10 explosives compounds and the samples were held at ambient temperatures (20 °C) for 85 d. Surface water represented three rivers with a range of total organic carbon concentrations and two rivers draining glacial watersheds with minimal organic carbon but high suspended solids. 18.2 MX deionized water exhibited no explosives transformation. Nitroaromatic compound loss from solution was generally: tetryl > 1,3,5-TNB > TNT > 1,3-DNB > 2,4-DNT. The HMX, RDX, 2,6-DNT, 2ADNT, and 4ADNT concentrations remained somewhat stable over time. The surface water with the highest total organic carbon concentration exhibited the most dramatic nitroaromatic loss from solution with tetryl, 1,3,5-TNB and TNT concentrations decreasing to below detection within 10 d. The two water samples with high suspended solid loads exhibited substantial nitroaromatic explosives loss which could be attributable to adsorption onto fresh mineral surfaces and/or enhanced microbiologic biotransformation on mineral surfaces. An identical set of six water samples was spiked with explosives and acidified with sodium bisulfate to a pH of 2. Acidification maintained stable explosives concentrations in most of the water samples for the entire 85 d. Our results suggest sampling campaigns for explosives in surface water must account for biogeochemical characteristics. Acidification of samples with sodium bisulfate immediately following collection is a robust way to preserve nitroaromatic compound concentrations even at ambient temperature for up to three months.