Читать книгу Global Approaches to Environmental Management on Military Training Ranges - Tracey Temple - Страница 19

With the increasing importance of IM, previously unused energetic materials such as NTO are becoming more common. NTO has been used in IHE fills such as PAX-21, IMX-101 and IMX-104 in combination with more conventional munition constituents such as RDX and NQ [7, 67]. There are some concerns with the use of NTO due to the increased residue deposition from both high and low order detonations of ordnance using IHE fill [50, 75]. In particular, sampling after blow-in-place detonations of IMX-104 60 mm and 81 mm mortars demonstrated that up to 50% NTO may be deposited on the range [50].

NTO is highly soluble in water (16 g l⁻¹) and dissolves in direct correlation with the volume of incident water, suggesting that it could quickly enter soil environments with transport highly dependent on the volume of rainfall [76, 77]. In addition, NTO does not sorb significantly to soil and therefore has the potential to be highly mobile [20]. Batch adsorption experiments with NTO have demonstrated very low adsorption to a variety of soils within the pH range 4.4–8.2, organic matter contents of 0.34%–5.25% and specific surface areas of 1.7–38.3 m² g⁻¹ [78].

Although NTO has the potential to be mobile, it is also susceptible to biodegradation with complete degradation observed within five weeks [57]. Degradation of NTO in aerobic soil cultures has been shown to occur through loss of nitrate followed by transformation to 1,2-dihydro-3H-1,2,4-triazol-3-one (ATO) (figure) [79]. However, NTO degradation by-products have yet to be detected in real soil environments, although ATO is expected to be the main intermediate before complete mineralisation [80]. Soil column studies with NTO have demonstrated that a significant percentage of NTO is rapidly biodegraded, particularly in soils with high organic content where in some cases it has not been possible to recover any of the energetic material [57, 81, 82]. Whereas in soil with low organic content, high proportions of NTO can be quickly transported with up to 100% recovery within a week [57, 81].

NTO is one of the least toxic explosives, with an oral LD₅₀ of >5000 mg kg⁻¹ in rats [83]. Rats exposed to 184 μg l⁻¹ for 4 h exhibited no adverse effects, which is a good indicator of low chronic toxicity in humans [84]. However, both NTO and ATO have anomalous effects on the development of zebrafish embryos, which have neurodevelopment processes homologous to those in humans, suggesting that NTO may cause reproductive toxicity [85]. NTO exposure to skin causes mild, short-term irritation [83], and can penetrate skin at 332 μg cm⁻² h⁻¹ [86]. Although considered less toxic than TNT, the higher solubility of NTO in water compared to other explosive compounds may cause water discoloration, even at low concentrations.