Chapter 2 - ‘Priority Pollutants’ and Chemicals of Emerging Concern
2.4.5 Chemicals of warfare
[NOTE: This section was written by Matt Bentley, PhD, who recently joined the project as a co-author. It’s available free-access to all email subscribes to honor Matt’s contributions to the project and highlight his work. I’m so happy to be able to work with Matt on this book…]
Most nations around the world are affected by the impacts of armed conflict, past or present. The environmental legacy of global munitions production, use, and disposal threaten water resources and human health in significant ways. Two primary types of “energetic” compounds that are released to the environment as a result of munitions production include explosives and propellants [161]. Common sources of toxic energetic compounds to the environment include: munitions production and disposal facilities, munitions storage sites, military training grounds, and active conflict zones [161, 162]. In many low and middle income countries unexploded ordnance from prior conflict as well as legacy land mines contribute significantly to the load of munitions-related toxic compounds in the environment [161]. Heavy metals (lead in particular) are also commonly released to the environment as a result of military activities [162].
Figure 2.5 Chemical structure of common munitions and ordnance compounds.
Explosive ordnance
2,4,6-trinitrotoluene (TNT) and hexa-hydro-1,3,5-trinitro-1,3,5-triazine (RDX) are the most widely used organic compounds in explosive ordnance. These compounds are classified as “possible human carcinogens” by the EPA and have lifetime drinking water Health Advisory Levels of 2 µg/L [163]. These compounds have explosive properties because they rapidly decompose into small gaseous molecules when energy is transferred to them as a result of thermal, electrical, or mechanical shock [162]. The nitro groups present in these compounds (Fig 2.5) are known to have both carcinogenic, neurotoxic, and mutagenic effects on organisms. Human exposure to TNT and RDX has led to development of cancers, seizure disorders, cataracts, anemia, liver disorders, and death [162, 164, 165]. Both TNT and RDX are highly mobile in water and have been frequently detected in groundwater sources near munitions production sites, active conflict zones, and military training facilities [161, 162], as well as in surface waters downstream of munitions production facilities[163]. These compounds become incorporated into plant structures in contaminated areas, leading to direct human exposure when contaminated soil or water is used for food production activities [161, 162]. Breakdown products of TNT and RDX could contribute to toxicity as well, as known degradation pathways include nitrosamine and nitroso intermediate products with known mutagenic and carcinogenic properties [166].
Propellants (rocket fuel)
Commonly used propellants in ordnance include perchlorate (inorganic) and nitroglycerine (organic). Nitroglycerine exposure has been linked to headaches, nausea, convulsions, hallucinations, circulatory collapse, and death[161]. Long term exposure to perchlorate interferes with iodine uptake in the thyroid gland, impacting hormones critical for normal growth and development of fetuses, infants, and young children [167]. Perchlorate has a WHO Guideline Value of 70 µg/L [7]. Perchlorate contamination has been found in areas where ordnance has been detonated such as active conflict zones and training facilities. It does not fully degrade with detonation, and is environmentally persistent and highly mobile in the aqueous phase [168]. Estimates indicates that a single PAX-21 mortar detonation could contaminate up to 35 million liters of water above the California State Drinking Water Limit for perchlorate (6 µg/L).
The most bombed region in the world: Southeast Asia
As a result of numerous past and present war and conflict episodes, unexploded ordnance (e.g., landmines, cluster bomb “duds”) pose significant risk across Southeast Asia. In addition to the direct risk of civilian casualty as a result of detonation, unexploded ordnance (UXO) presents a significant health risk as a result of environmental contamination [161]. Estimates place up to 800,000 tons of war-era ordinance and three million landmines remaining in Vietnam alone [161]. Vietnam also has long term agent orange/dioxin contamination at former US military sites that contribute to high dioxin loads in human tissues in surrounding areas [169]. In Laos, one-third of the two million tons of cluster bomb ordnance dropped during the Vietnam War are estimated to remain as UXO [170-172]. There are other Southeast Asian nations that are dealing with long term UXO issues associated with war, and Myanmar/Burma is actively adding landmines in regions populated by minority tribal groups [173].
In addition to ordnance manufacturing and storage facilities, landmines and UXO contribute to environmental occurrence and human exposure to explosive compounds [161, 162]. UXO degrade and leach toxins over time. Explosive compounds and their degradates impact surface water and groundwater, and can sorb to soils and contaminate vegetables, leading to chronic human exposures [161, 174]. The occurrence of explosives and propellants in the environment has not been well characterized in low income countries, particularly in areas affected by UXO. The risk of human exposure to toxic munitions compounds in Southeast Asia deserve increased attention, particularly those areas affected by past or present conflict.
RDX: the explosive with global collateral damage
Research Department Explosive, or RDX, was developed during WWII to improve on conventional explosive compounds used in warfare such as TNT. Its widespread manufacture began in the US in 1941. RDX made possible many novel weapons of modern warfare, e.g., antitank missiles, plastic explosives, underwater bombs, and it is now a component of nearly all explosive devices. RDX arguably won the war against Nazi Germany – but it came at great cost to US communities whose local environments and drinking water sources were polluted with toxic munitions residues from the manufacture of RDX and other explosives.
Ironically, Quaker Oats, a cereal company with a pacifist Quaker mascot, manufactured RDX for the US military under their subsidiary, Quaker Oats Ordnance Corps at the Cornhusker Army Ammunition Plant near Grand Island, Nebraska. The Holston Army Ammunition Plant in Kingsport, Tennessee (currently the only remaining manufacturer of RDX in the US) was over a period of years releasing up to 68 pounds of waste RDX into the Holston River each day. Widespread groundwater contamination has been found near ammunitions manufacturing facilities across the United States, and “pink water” contaminated by RDX, TNT, and other energetic compounds had been released into soil and surface waters near munitions manufacturing facilities, resulting in widespread environmental and drinking water contamination.
Unpublished studies by the US EPA and Department of Defense (DOD) indicated that RDX is environmentally persistent and mobile in the aqueous phase, as well as highly toxic and carcinogenic. The EPA eventually classified RDX as a “possible human carcinogen”, although there is sufficient evidence to warrant “likely carcinogen” status. The DOD has funded numerous health studies that downplay the toxic and carcinogenic impacts of RDX. Furthermore, the DOD has reportedly pressured the EPA to reject a proposed RDX regulations, as this would necessitate massive investment in environmental remediation of contaminated military sites. Collateral damage to the domestic environment and civilian health have been considered an “acceptable cost” for maintaining the US’ capabilities to project military strength abroad.
For more on RDX, see the ProPublica feature “The Bomb that Went Off Twice” and the “Bombs in Your Backyard” interactive map and database of ordnance contamination in the United States.
Selecting a sentinel warfare compound
Selecting a sentinel compound for this broad class of environmental contaminants is challenging, as this class includes compounds with very different structures and physicochemical properties. RDX is a good candidate as it meets all of the sentinel criteria: (1) heavily used and widely occurring, (2) environmentally persistent, (3) toxicologically relevant, and (4) difficult to treat by adsorption. RDX has been frequently detected in aqueous samples near military installations, and is environmentally persistent compared with other explosive compounds such as TNT and nitroglycerine. In addition, RDX is more mobile in water and presents a likely threat of groundwater contamination. RDX has been frequently detected in surface waters downstream of munitions production or processing facilities. Unexploded ordnance could also be a contributing source of RDX in surface water and groundwater, particularly in low income countries with past or ongoing military conflict.
You might ask – what about Agent Orange? It’s perhaps the most notorious chemical heavily used during the wars of the 20th Century. Why not choose Agent Orange as a sentinel chemical? In a sense, we already have. Agent Orange, a defoliant, is primarily a mixture of two herbicides 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 2,4-D. 2,4-D is, of course, our weakly adsorbing sentinel herbicide. As nasty as chlorophenoxy acetic acid herbicides are, however, the most insidious component of Agent Orange was an impurity, not one of the two main active ingredients. The Agent Orange manufacture process left small quantities of dioxin present in the mix. Most of the dioxin impurity present was the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) congener, which is one of the most toxic organic chemicals known to science. If there can be any good news about dioxin chemicals like TCDD, it’s that they’re highly hydrophobic and strongly adsorbing. Thus, they don’t meet our sentinel criteria (4) of being difficult to treat by adsorption compared with far more water-soluble compounds like 2,4-D or RDX.
RDX