Editing TNT (section)

== Ecological impact ==
Because of its suitability in construction and demolition, TNT has become the most widely used explosive and thus its toxicity is the most characterized and reported. Residual TNT from manufacture, storage, and use can pollute water, soil, the [[atmosphere]], and the [[biosphere]].<ref>{{cite report |url=https://www.environment.gov.au/system/files/resources/bc0e52ba-8f78-4ce1-83b4-4910f4a1f0e9/files/hazardous-waste-impacts.pdf |title=The health and environmental impacts of hazardous wastes: Impact Profiles |author=Ascend Waste and Environment |website=awe.gov.au |date=7 June 2015 |access-date=22 April 2022}}</ref>

The concentration of TNT in contaminated soil can reach 50 g/kg of soil, where the highest concentrations can be found on or near the surface. In September 2001, the [[United States Environmental Protection Agency]] (USEPA) declared TNT a pollutant whose removal is a priority.<ref name="Esteve-Nunez_2001">{{cite journal|year=2001|title=Biological degradation of 2,4,6-trinitrotoluene|journal=Microbiol. Mol. Biol. Rev.|volume=65|issue=3|pages=335–52, table of contents|doi=10.1128/MMBR.65.3.335-352.2001|pmc=99030|pmid=11527999|vauthors=Esteve-Núñez A, Caballero A, Ramos JL}}</ref> The USEPA maintains that TNT levels in soil should not exceed 17.2 milligrams per kilogram of soil and 0.01 milligrams per litre of water.<ref name="Ayoub_2010">{{cite journal|year=2010|title=Application of advanced oxidation processes for TNT removal: A review|journal=J. Hazard. Mater.|volume=178|issue=1–3|pages=10–28|doi=10.1016/j.jhazmat.2010.02.042|pmid=20347218|vauthors=Ayoub K, van Hullebusch ED, Cassir M, Bermond A}}</ref>

=== Aqueous solubility ===
[[Dissolution (chemistry)|Dissolution]] is a measure of the rate that solid TNT in contact with water is dissolved. The relatively low [[Solubility|aqueous solubility]] of TNT causes solid particles to be continuously released to the environment over extended periods of time.<ref name="Pichtel_2012">{{cite journal|date=2012|title=Distribution and Fate of Military Explosives and Propellants in Soil: A Review|journal=Applied and Environmental Soil Science|volume=2012|pages=1–33|doi=10.1155/2012/617236|author=Pichte J|issue=1 |doi-access=free|bibcode=2012ApESS201217236P }}</ref>  Studies have shown that TNT dissolves more slowly in saline water than in freshwater. However, when salinity is altered, TNT dissolves at the same speed.<ref name="pmid15757688">{{cite journal|year=2005|title=Comparison of environmental fate and transport process descriptors of explosives in saline and freshwater systems|journal=Mar. Pollut. Bull.|volume=50|issue=3|pages=247–51|doi=10.1016/j.marpolbul.2004.10.008|pmid=15757688|vauthors=Brannon JM, Price CB, Yost SL, Hayes C, Porter B|bibcode=2005MarPB..50..247B }}</ref>  Because TNT is moderately soluble in water, it can migrate through subsurface soil, and cause [[groundwater]] contamination.<ref name="pmid12187997">{{cite journal|year=2002|title=Detection of explosives and their degradation products in soil environments|journal=J Chromatogr A|volume=963|issue=1–2|pages=411–8|doi=10.1016/S0021-9673(02)00553-8|pmid=12187997|vauthors=Halasz A, Groom C, Zhou E, Paquet L, Beaulieu C, Deschamps S, Corriveau A, Thiboutot S, Ampleman G, Dubois C, Hawari J}}</ref>

=== Soil adsorption ===
[[Adsorption]] is a measure of the distribution between soluble and sediment adsorbed contaminants following attainment of equilibrium. TNT and its transformation products are known to adsorb to surface soils and sediments, where they undergo reactive transformation or remained stored.<ref name="pmid19329139">{{cite journal|year=2009|title=A time series investigation of the stability of nitramine and nitroaromatic explosives in surface water samples at ambient temperature |journal=Chemosphere |volume=76 |issue=1 |pages=1–8 |doi=10.1016/j.chemosphere.2009.02.050 |pmid=19329139 |vauthors=Douglas TA, Johnson L, Walsh M, Collins C |bibcode=2009Chmsp..76....1D|url=https://zenodo.org/record/851720}}</ref>  The movement or organic contaminants through soils is a function of their ability to associate with the mobile phase (water) and a stationary phase (soil). Materials that associate strongly with soils move slowly through soil. The association constant for TNT with soil is 2.7 to 11 L/kg of soil.<ref name="Haderlein_1996">{{cite journal|date=January 1996|title=Specific Adsorption of Nitroaromatic Explosives and Pesticides to Clay Minerals|journal=Environmental Science & Technology|volume=30|issue=2|pages=612–622|doi=10.1021/es9503701|vauthors=Haderlein SB, Weissmahr KW, Schwarzenbach RP|bibcode=1996EnST...30..612H}}</ref>  This means that TNT has a one- to tenfold tendency to adhere to soil particulates than not when introduced into the soil.<ref name = "Pichtel_2012"/>   [[Hydrogen bonding]] and [[ion exchange]] are two suggested mechanisms of adsorption between the nitro functional groups and soil colloids.

The number of [[functional group]]s on TNT influences the ability to adsorb into soil. Adsorption coefficient values have been shown to increase with an increase in the number of amino groups. Thus, adsorption of the TNT decomposition product 2,4-diamino-6-nitrotoluene (2,4-DANT) was greater than that  for 4-amino-2,6-dinitrotoluene (4-ADNT), which was greater than that for TNT.<ref name = "Pichtel_2012"/>   Lower adsorption coefficients for 2,6-DNT compared to 2,4-DNT can be attributed to the [[Steric effects|steric]] hindrance of the NO<sub>2</sub> group in the [[Arene substitution pattern|ortho position]].

Research has shown that in freshwater environments, with high abundances of Ca<sup>2+</sup>, the adsorption of TNT and its transformation products to soils and sediments may be lower than observed in a saline environment, dominated by K<sup>+</sup> and Na<sup>+</sup>. Therefore, when considering the adsorption of TNT, the type of soil or sediment and the ionic composition and strength of the ground water are important factors.<ref name="Pennington_2002">{{cite journal|date=February 2002|title=Environmental fate of explosives|journal=Thermochimica Acta|volume=384|issue=1–2|pages=163–172|doi=10.1016/S0040-6031(01)00801-2|vauthors=Pennington JC, Brannon JM|bibcode=2002TcAc..384..163P }}</ref>

The association constants for TNT and its degradation products with clays have been determined. Clay minerals have a significant effect on the adsorption of energetic compounds. Soil properties, such as organic carbon content and cation exchange capacity have significant impacts on the adsorption coefficients.

Additional studies have shown that the mobility of TNT degradation products is likely to be lower "than TNT in subsurface environments where specific adsorption to clay minerals dominates the sorption process."<ref name = "Pennington_2002"/>  Thus, the mobility of TNT and its transformation products are dependent on the characteristics of the sorbent.<ref name = "Pennington_2002"/> The mobility of TNT in groundwater and soil has been extrapolated from "sorption and desorption [[Isothermal process|isotherm models]] determined with [[humic acids]], in aquifer sediments, and soils".<ref name = "Pennington_2002"/>  From these models, it is predicted that TNT has a low retention and transports readily in the environment.<ref name = "Esteve-Nunez_2001"/>

Compared to other explosives, TNT has a higher association constant with soil, meaning it adheres more with soil than with water. Conversely, other explosives, such as [[RDX]] and [[HMX]] with low association constants (ranging from 0.06 to 7.3 L/kg and 0 to 1.6 L/kg respectively) can move more rapidly in water.<ref name = "Pichtel_2012"/>

=== Chemical breakdown ===
TNT is a reactive molecule and is particularly prone to react with reduced components of sediments or [[photodegradation]] in the presence of sunlight. TNT is thermodynamically and kinetically capable of reacting with a wide number of components of many environmental systems. This includes wholly abiotic reactants, like [[hydrogen sulfide]], [[ferrous|Fe<sup>2+</sup>]], or microbial communities, both oxic and anoxic and photochemical degradation.{{Cn|date=January 2021}}

Soils with high clay contents or small particle sizes and high [[Total organic carbon|total organic carbon content]] have been shown to promote TNT transformation. Possible TNT transformations include [[Reduction reaction|reduction]] of one, two, or three nitro-moieties to amines and coupling of amino transformation products to form [[dimer (chemistry)|dimer]]s. Formation of the two monoamino transformation products, 2-ADNT and 4-ADNT, is energetically favored, and therefore is observed in contaminated soils and ground water. The diamino products are energetically less favorable, and even less likely are the triamino products.{{Cn|date=January 2021}}

The transformation of TNT is significantly enhanced under anaerobic conditions as well as under highly reducing conditions. TNT transformations in soils can occur both biologically and abiotically.<ref name = "Pennington_2002"/>

[[Photolysis]] is a major process that impacts the transformation of energetic compounds. The alteration of a molecule in photolysis occurs by direct absorption of light energy or by the transfer of energy from a photosensitized compound. [[Phototransformation]] of TNT "results in the formation of [[nitrobenzene]]s, [[benzaldehyde]]s, azodicarboxylic acids, and [[nitrophenol]]s, as a result of the [[oxidation]] of [[methyl group]]s, reduction of [[nitro compound|nitro groups]], and dimer formation."<ref name = "Pichtel_2012"/>

Evidence of the photolysis of TNT has been seen due to the color change to pink of TNT-containing wastewaters when exposed to sunlight. Photolysis is more rapid in river water than in distilled water. Ultimately, photolysis affects the fate of TNT primarily in the aquatic environment but could also affect the fate of TNT in soil when the soil surface is exposed to sunlight.<ref name = "Pennington_2002"/>

=== Biodegradation ===
The ligninolytic physiological phase and manganese peroxidase system of fungi can cause a very limited amount of mineralization of TNT in a liquid culture, though not in soil. An organism capable of the remediation of large amounts of TNT in soil has yet to be discovered.<ref name="pmid11131384">{{cite journal|year=2000|title=Microbial degradation of explosives: biotransformation versus mineralization|journal=Appl. Microbiol. Biotechnol.|volume=54|issue=5|pages=605–18|doi=10.1007/s002530000445|pmid=11131384|vauthors=Hawari J, Beaudet S, Halasz A, Thiboutot S, Ampleman G|s2cid=22362850}}</ref> Both wild and transgenic plants can [[Phytoremediation|phytoremediate]] explosives from soil and water.<ref name="pmid22996005">{{cite journal|year=2012|title=Phytoremediation of explosives (TNT, RDX, HMX) by wild-type and transgenic plants|journal=J. Environ. Manage.|volume=113|pages=85–92|doi=10.1016/j.jenvman.2012.08.016|pmid=22996005|vauthors=Panz K, Miksch K|bibcode=2012JEnvM.113...85P }}</ref>