Global Approaches to Environmental Management on Military Training Ranges. Tracey Temple
NC, and so areas where high quantities of NC propellants are in use have been more difficult to analyse [64].
NC is insoluble in water and tends to be deposited on the soil surface in fibrous strands, rather than particles. NC is susceptible to biodegradation to a non-energetic polymer through the loss of nitrogen [64]. NC is not toxic towards humans, animals or plants due to the difficulty of absorption through the intestines and insolubility in water [65]. Deposition of NC on ranges does not have a significant environmental impact on receptors, other than an unnatural presence in the environment, and therefore has not been subject to intense scrutiny compared to high explosives such as TNT and RDX.
NG is soluble in water, and does not tend to sorb significantly to soil so it is quite mobile in soil environments [64]. Under favourable soil conditions NG undergoes several stages of biodegradation and can ultimately form glycerol, and in some cases carbon dioxide. However, in reality not all NG will be completely biodegraded, and in sandy soils where attenuation is poor it is unlikely that NG will be significantly biodegraded before migration to groundwater [66]. Photodegradation of NG occurs more quickly when it is solubilised in water, with a half-life of weeks. Some degradation products are more toxic than NG itself, therefore if NG contamination is suspected it is recommended that samples are also tested for mono and di-nitroglycerine [29].
NQ is a common component of propellants, but has also recently been used in the IHE IMX-101 in combination with DNAN and NTO [67]. Research has suggested that a higher percentage of residue may be deposited from IHEs compared to conventional explosives such as Comp B, even for high order detonations [51, 68]. Therefore, higher quantities of NQ may be deposited on ranges in the future. NQ is fairly water soluble (2.6 g l−1) and does not sorb significantly to soil. NQ has been found to be biodegraded in some soils to ammonia and nitrous oxide, particularly soils with high organic carbon content but it may migrate too quickly through soil for any significant degradation to occur before reaching groundwater [69]. Photodegradation of NQ gives guanidine, urea and cyanoguanidine.
Perchlorate is a naturally occurring and man-made anion that contains one chlorine atom bonded to four oxygen atoms ClO4−. It is commonly produced when energetic compositions in the form of ammonium perchlorate (AP), sodium perchlorate and potassium perchlorate dissolve in water. Ammonium perchlorate is a key component of PAX-21, an IHE fill also containing DNAN and RDX, which now has restrictions on use due to the significant quantities of AP deposited during detonation (averaging 15% during high order detonations) [8, 70].
Perchlorates are generally soluble and stable in water and do not sorb significantly to soil and therefore have a great potential to contaminate surface and groundwater. Incidences of significant groundwater contamination from military use of perchlorates in North America have been well documented [70, 71]. A risk assessment of UK use of perchlorate highlighted that monitoring for AP in potable water sources is not widespread in the UK, but that high levels of AP have been detected in the groundwater at Shoeburyness disposal range where 14.5 tonnes of propellant have been disposed of since 1993 [72]. While drinking and groundwater limits have not been set for the UK, where contamination has occurred the UK uses the limit of detection (1 μg l−1) as an indication of acceptable levels. The presence of perchlorate in drinking water is a particular concern as it is known to cause abnormal thyroid function in humans [73, 74].
1.3.4 3-Nitro-1,2,4-triazol-5-one
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