Photolysis of dinitrobenzyl alcohols, dinitrobenzaldehydes, and nitrobenzoic acids in seawater, estuary water, and pure water

Photolytic transformation of the propellants 2,4-dinitrotoluene (2,4-DNT) and 2,6-dinitrotoluene (2,6-DNT) produces 2,4-dinitrobenzyl alcohol (2,4-DNBOH), 2,6-dinitrobenzyl alcohol (2,6-DNBOH), 2,4-dinitrobenzaldehyde (2,4-DNBCHO), 2,6-dinitrobenzaldehyde (2,6-DNCHO), 2,4-dinitrobenzoic acid (2,4-DNBCOOH) and 2-amino 4-nitrobenzoic acid (2A4NBA). In this work, the photolysis rates of the products of the parent dinitrotoluenes in both natural and laboratory-prepared waters were measured. The photochemical degradation was studied using a Suntest CPS+® solar simulator equipped with various filters designed to select specific regions of the solar spectrum. HPLC analysis was used to determine the degradation rates of the compounds. Photolysis rates of the alcohols and aldehydes were influenced by the wavelength of the light irradiating the compound; 295, 305, and 320 nm long-pass filter exposures produced similar rates of degradation while the 395 nm filter exposure produced minimal degradation. Under the 295-nm filter, the first-order degradation rate constants were highest for 2,6-DNBOH (4 h− 1), followed by 2,4-DNBCHO and 2,6-DNBCHO (3 h− 1), with the smallest for 2,4-DNBOH (2 h− 1). The aqueous phase composition (filtered seawater, estuary water, ultrapure water) had minimal impact on the photolysis rates. All four compounds were degraded faster than the parent 2,4-DNT and 2,6-DNT. In contrast, the 2,4-DNBCOOH and 2A4NBA were not photolyzed under any of the conditions studied.