Explosives - Nitroaromatics
Nitroaromatics form an important group of recalcitrant xenobiotics. Only few aromatic compounds, bearing one nitro group as a substituent of the aromatic ring, are produced as secondary metabolites by microorganisms. The majority of nitroaromatic compounds in the biosphere are industrial chemicals such as explosives, dyes, polyurethane foams, herbicides, insecticides and solvents.
Detection of unrecovered land mines is a growing international problem. Unrecoverd land mines are a legacy that continues to harm people long after the hostilities cease. The most widely used tool for land mine detection today is the hand-held metal detector. Other methods for landmine detection are limited due to their high false alarm rate. Chemical sensors have been investigated for mine detection. For chemical species having favorable spectral properties, remote sensing can be achieved by fluorescence light detection and ranging LIDAR. Nitroaromatic explosives exhibit strong ultraviolet absorption but low fluorescence, thus direct detection is not practical. Indirect detection in soil can be obtained using a synthetic chemical polymer that exhibits a change in fluorescence in the presence of an explosive compound.
Penetration of nitroaromatic compounds through the skin is a major concern for the military. An important characteristic of nitroaromatic compounds is their ability to rapidly penetrate the skin. They can cause the formation of methemeglobin on acute exposures and anemia on chronic exposures. Additionally, local irritation, liver damage and bladder tumors have also been identified.
These compounds are generally recalcitrant to biological treatment and remain in the biosphere, where they constitute a source of pollution due to both toxic and mutagenic effects on humans, fish, algae and microorganisms. However, relatively few microorganisms have been described as being able to use nitroaromatic compounds as nitrogen and/or carbon and energy source.
However, relatively few microorganisms have been described as being able to use nitroaromatic compounds as nitrogen and/or carbon and energy source. The best-known nitroaromatic compound is the explosive TNT (2,4,6-trinitrotoluene).
The optimal remediation strategy for nitroaromatic compounds depends on many site-specific factors. Composting and the use of reactor systems lend themselves to treating soils contaminated with high levels of explosives (e.g. at former ammunition production facilities, where areas with a high contamination level are common). Compared to composting systems, bioreactors have the major advantage of a short treatment time, but the disadvantage of being more labour intensive and more expensive.
TNT is one of the most common bulk explosives. 2,4,6 Trinitrotoluene (TNT) is an explosive used in military munitions and in civilian mining and quarrying activities. TNT was first used on a wide scale during World War I and is still used today. The United States military stopped production of TNT in the mid-1980s.
TNT is classified as a secondary explosive because it is less susceptible to initiation and requires a primary or initiating explosive to ignite it. TNT can be used as a booster or as a bursting charge for high-explosive shells and bombs. Also, TNT may be mixed with other explosives such as Royal Demolition Explosive (RDX) and High Melting Explosive (HMX) and it is a constituent of many explosives, such as amatol, pentolite, tetrytol, torpex, tritonal, picratol, ednatol, and ¿Composition B¿. It has been used under such names as Triton, Trotyl, Trilite, Trinol, and Tritolo.
The advantages of TNT include low cost, safety in handling, fairly high explosive power, good chemical and thermal stability, compatibility with other explosives, a low melting point favorable for melt casting operations and moderate toxicity.
TNT is a crystalline substance. The importance of TNT as a military explosive is based upon its relative safety in manufacture, loading, transportation, and stowage, and upon its explosive properties. Manufacturing yields are high and production relatively economical. The chemical names for TNT are trinitrotoluene and trinitrotol. Other (commercial) names are Trilite, Tolite, Trinol, Trotyl, Tritolol, Tritone, Trotol, and Triton. TNT is toxic, odorless, comparatively stable, nonhygroscopic, and relatively insensitive. When TNT is pure, it is known as grade A TNT and varies from white to pale yellow. When the proportion of impurities is much greater, the color is darker, often brown, and the chemical is known as grade B TNT. It maybe ignited by impact, friction, spark, shock, or heat. TNT does not form sensitive compounds with most metals. The melting point varies between 80.6°C for grade A (refined TNT) and 76°C for grade B (crude TNT).
TNT does not appear to be affected by acids but is affected by alkalies (lye, washing soda, and so on), becoming pink, red, or brown, and more sensitive. It is practically insoluble in water, but soluble in alcohol, ether, benzene, carbon disulfide, acetone, and certain other solvents. The velocity of detonation is approximately 22,300 fps.
Exudate has been known to separate from cast TNT. It may appear pale yellow to brown and may vary in consistency from an oily liquid to a sticky substance. The amount and rate of separation depend primarily upon the purity of the TNT and, secondarily, upon the temperature of the stowage place. Grade B (low-melting point) TNT may exude considerable liquid and generate some gas. This exudation is accelerated with an increase in temperature. Pure TNT will not exude since exudate consists of impurities that have not been extracted in the refining process. Exudate is a mixture of lower melting isomers of TNT, nitrocompounds of toluene of lower nitration, and possible nitrocompounds of other aromatic hydrocarbons and alcohols. It is flammable and has high sensitivity to percussion when mixed with absorbents. Its presence does no appreciable harm to the stability but somewhat reduces the explosive force of the main charge.
In some ammunition, an inert wax pad is used in the loading operation, and, in some cases, waxy material may ooze from the case. It should not be confused with the TNT exudate previously described. This material should, however, be tested for TNT to confirm its actual composition, TNT exudate, when mixed with a combustible material, such as wood chips, sawdust, or cotton waste, will form a low explosive that is highly flammable and ignites easily from a small flame. It can be exploded in a reamer similar to a low grade of dynamite, but the main danger is its fire hazard. Accumulation of exudate is considered a great risk of explosion and fire. Its accumulation should always be avoided by continual removal and disposal as it occurs. While TNT is no longer used in Navy gun ammunition, some 3"/50, 40-mm, and 20-mm stocks loaded with TNT may still be in the inventory. These stocks should be identified and checked periodically for the presence of exudate. The exudate is soluble in acetone or alcohol. One of these solvents (requiring adequate ventilation) or clean, hot water should be used to facilitate removal and disposal of the exudate.
Under no circumstances should soap or other alkaline preparations be used to remove this exudate. The addition of a small amount of hydroxide, caustic soda, or potash will sensitize TNT and cause it to explode if heated to 160°F.
During production TNT is in the form of a liquid which is then cooled and washed with water to form solid flakes in the form of colorless crystals, though commercial crystals are yellow. The flakes can be remelted at low temperatures (180 degrees Fahrenheit) and poured into munitions shells and casings. TNT was widely used by the military because of its low melting point and its resistance to shock or friction which allows it to be handled, stored, and used with comparative safety.
In order to detonate, TNT must be confined in a casing or shell and subjected to severe pressures and/or temperatures (936 degrees Fahrenheit) such as from a blasting cap or detonator. In fact, U.S. Army tests on pure TNT show that when struck by a rifle bullet TNT failed to detonate 96% of the time and when dropped from an altitude of 4,000 feet onto concrete, a TNT filled bomb failed to explode 92% of the time.
2,4,6-Trinitrotoluene (TNT) causes liver damage and aplastic anemia. Deaths from aplastic anemia and toxic hepatitis were reported in TNT workers prior to the 1950s. With improved industrial practices, there have been few reports of fatalities or serious health problems related to its use.
Exposures at or below 0.5 mg/m3 have been reported to cause destruction of red blood cells. Among some groups of workers, there is a reduction in average hemoglobin and hematocrit values. Workers deficient in glucose-6-phosphate dehydrogenase may be particularly at risk of acute hemolytic disease. Three such cases occurred after a latent period of 2 to 4 days and were characterized by weakness, vertigo, headache, nausea, paleness, enlarged liver and spleen, dark urine, decreased hemoglobin levels, and reticulocytosis. Although no simultaneous measurements of atmospheric levels were available, measurement on other occasions showed exposure levels up to 3.0 mg/m3.
Cataracts are also reportedly produced with chronic exposures for more than 5 years. The opacities did not interfere with visual acuity or visual fields. The induced cataracts may not regress once exposure ceases, although progression is arrested.
The vapor or dust can cause irritation of mucous membranes resulting in sneezing, cough, and sore throat. Although intense or prolonged exposure to TNT may cause some cyanosis, it is not regarded as a strong producer of methemoglobin. Other occasional effects include leukocytosis or leukopenia, peripheral neuritis, muscular pains, cardiac irregularities, and renal irritation.
Trinitrotoluene is absorbed through skin fairly rapidly, and reference to airborne levels of vapor or dust may underestimate total systemic exposure if skin exposure also occurs. Apparent differences in dose-response relationships based only on airborne levels may be explained by differences in skin contact. TNT causes sensitization dermatitis; the hands, wrist, and forearms most commonly are affected, but skin at friction points such as the collar line, belt line, and ankles also is often involved. Erythema, papules, and an itchy eczema can be severe. The skin, hair, and nails of exposed workers may be stained yellow.
Rats administered 50 mg/kg/day in their diets had anemia, splenic lesions, and liver and kidney damage. Hyperplasia and carcinoma of the urinary bladder also were observed in female rats.
Historically, control of exposure to TNT has been accomplished through general safety and hygiene measures, yet additional, specific measures are necessary. The Hazard Communication Program, for example, should instruct workers about the need for strict personal and shop hygiene, and about the hazards of the particular operations that are conducted in that plant. In addition, soap that contains 5% to 10% potassium sulfite will not only help remove TNT dust from the skin, suds that turn red will also indicate any remaining contamination. Furthermore, respiratory protection equipment should be selected according to NIOSH guidance, and should be worn during operations that release dust, vapor, or fumes.
Before WWII, research suggested that improving the nutritional status of TNT workers might help improve their resistance to toxic effects. However, in a World War II era cohort study, multivitamin capsules were not shown to be efficacious in preventing TNT toxicity.
TNT interacts with certain medications - including isoniazid, phenylbutazone, phenytoin, and methotrexate. Anyone taking these medications while working with TNT should be closely followed by the occupational physician.
Medical Monitoring. The U.S. Army currently recommends preplacement and periodic (semiannual) examinations of TNT workers. To identify workers with higher-than-normal sensitivity to TNT toxicity during the first three months of exposure, monthly hemoglobin, LDH, and AST should be done.
The ACGIH TLV Committee for Chemical Substances recommended that the 8-hour TLV for TNT be lowered from 0.5 mg/m3 to 0.1 mg/m3 on 21 May 1997 after reviewing scientific reports of human and animal exposure. In some studies, evidence of liver toxicity, changes in blood cell production, and cataracts were noted when exposure levels ranged below 0.5 mg/m3 (the old ACGIH TLV). TNT workers should never be exposed to ambient levels of TNT above 0.1 mg/m3 for an 8-hour time weighted average (TWA) without appropriate respiratory protection. Based on the evidence reviewed by the ACGIH, the extra margin of safety afforded by this lowered TLV is necessary to protect workers health. Skin absorption has also been noted to be a significant means of exposure in several studies. Dermal exposure over an 8 hour period cannot be readily quantitated at a worksite, however use of protective clothing to include head cover and impermeable gloves is essential to prevent skin absorption of TNT.
2,4-DNT and 2,6-DNT are pale yellow solids with a slight odor and are two of the six forms of the chemical called dinitrotoluene (DNT). The other four forms (2,3-DNT, 2,5-DNT, 3,4-DNT, and 3,5-DNT) only make up about 5% of the technical grade DNT. DNT is not a natural substance but rather is usually made by reacting toluene (a solvent) with mixed nitric and sulfuric acids, which are strong acids. DNT is used to produce flexible polyurethane foams used in the bedding and furniture industry. DNT is also used to produce ammunition and explosives and to make dyes. It is also used in the air bags of automobiles.
It has been found in the soil, surface water, and groundwater of at least 122 hazardous waste sites that contain buried ammunition wastes and wastes from manufacturing facilities that release DNT. DNT does not usually evaporate and is found in the air only in manufacturing plants. DNT also does not usually remain in the environment for a long time because it is broken down by sunlight and bacteria into substances such as carbon dioxide, water, and nitric acid.
Workers who have been exposed to 2,4-DNT showed a higher than normal death rate from heart disease. However, these workers were exposed to other chemical as well. 2,4- and 2,6-DNT may also affect the nervous system and the blood of exposed workers. One study showed that male workers exposed to DNT had reduced sperm counts, but other studies did not confirm this finding.
The synthetic compound 1,3,5-TNB is used as a high explosive for commercial mining and military
use, as a narrow-range pH indicator and as an agent to vulcanize natural rubber. The compound is a manufacturing by-product of the explosive, TNT, and is released to the environment in discharged wastewater. Additionally, any TNT itself that is present in the waste stream may be degraded
to 1,3,5-TNB by photolysis under certain conditions of pH and organic matter content. The compound has a close structural relationship with the most widely produced military explosive, trinitrotoluene (TNT), of which it is a manufacturing by-product and an environmental degradation product.
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