Читать книгу Global Approaches to Environmental Management on Military Training Ranges - Tracey Temple - Страница 18

Nitroglycerin (NG), NQ, 2,4-DNT and 2,6-DNT have been detected at firing points on many US training ranges [9]. Studies have also found high concentrations of perchlorates [36]. The presence of NC on firing ranges has not been extensively investigated as it tends to be deposited as discrete fibres that are difficult to quantify [9]. An added complication is the tendency for other explosives to sorb onto 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].