Bryony Maskell reflects on developments in the hundred years since chemical weapons fell under the first effective international prohibition treaty.
Article from Responsible Science Journal, no. 8, Spring 2026. Advance online publication: 10 February 2026.
One hundred years ago, in 1925, in response to the use of poison gases in World War One (WWI), the Geneva Protocol came into effect. This one-page international agreement aimed to prohibit the use of chemical and biological warfare; however, it did not prohibit the development or production of chemical and biological weapons. While it was not the first attempt to control this type of warfare, this agreement helped lay the legal foundations to shape future agreements, including the comprehensive bans in the 1993 Chemical Weapons Convention (CWC).
Ancient chemical warfare
A chemical weapon is “a chemical used to cause intentional death or harm through its toxic properties” (Organisation for the Prohibition of Chemical Weapons (OPCW), n.d. a). Such weapons have likely been used since armed conflicts began. One of the earliest known examples of chemical weapon use involved wood impregnated with pitch and sulphur being ignited by Spartan soldiers in the siege of Plataea in the Fifth Century BCE, to release toxic sulphur dioxide (Jacob, 2017). Another notable example of ancient chemical weapon use is Greek Fire, an incendiary weapon of unknown composition that combusted spontaneously and could not be extinguished with water, first used by the Greeks in the Seventh Century (Encyclopædia Britannica, n.d.).
Early agreements
Prior to the 1925 Geneva Protocol, there were several attempts to control the use of chemical agents in warfare, as shown in Figure 1.
Figure 1: Early agreements on chemical weapons before WWI
Modern chemical warfare
Many of these prohibitions were ignored up to and during WWI, and thus began the era of modern chemical weapons, in which chemical agents were deployed on a large scale in combat. Examples of these chemical agents are shown in Figure 2. In WWI, all parties used an estimated 124,000 tons of chemical weapons, which are often referred to as gases despite some being liquids dispersed as aerosols, with up to 3% of all fatalities estimated as being due to ‘gas’ attacks. While the fatalities from chemical weapons are significantly less than from artillery, the lasting injuries and physiological effects from ‘gas’ attacks helped the issue become more topical, creating momentum that led to the Geneva Protocol (Harigel, 2001).
Figure 2: Chemical Weapons in WWI (Adapted from Brunning, 2014a)
Geneva Protocol
The Geneva Protocol (1925) was the first agreement to prohibit chemical and biological warfare following their large-scale use during WWI , and it is only a page long. The agreement prohibits the use of “asphyxiating, poisonous or other gases, and of all analogous liquids, materials or devices” and “bacteriological methods of warfare,” but does not prohibit the production or development of chemical and biological weapons or call for the destruction or reduction of these weapons (OPCW, 2015). Furthermore, this agreement was only between the signatories, and if one party violated the agreement, the other parties would have the right to retaliate (Zanders, 2025). Notably, this was the first time biological methods of warfare were considered in such an agreement, likely due to the “ambitious biological warfare campaign” by Germany during WWI, which included targeting animals to disrupt supply chains (Nikolakakis et. al., 2024). As of 2020, 146 states were party to the agreement (ICRC, n.d. e).
Nerve agents
Despite the prohibition of the use of chemical weapons, the Geneva Protocol allowed the production of new weapons, and so failed to prevent the subsequent development of nerve agents. Some of these are liquids, some are powders, and some exist as binary agents (where two less toxic precursors are stored and, when mixed, create the agents). These can be dispersed through liquid sprays or vapours, or through the contamination of food and water (British Broadcasting Corporation (BBC), 2017; 2020). Nerve agents cause damage through contact with the skin, ingestion, and inhalation. They interfere with the function of the nervous system and even the smallest amount can cause a variety of debilitating injuries or death (ATSDR, n.d.). Figure 3 shows information on some of the G series, V series and Novichok nerve agents.
Figure 3 – Nerve Agents, adapted from Brunning, 2014b; 2015; 2018
Use after the Geneva Protocol
Since the Geneva Protocol, neither chemical nor biological weapons have been used on the same scale in combat as in WWI; however, they have been used despite the prohibition. Examples of the use of chemical weapons between the Geneva Protocol and before the 1993 Chemical Weapons Convention (CWC) are included in Figure 4.
Figure 4 – Examples of chemical weapons use between 1925 and 1993 (Adapted from Zanders, 2019)
After WWII, much of Germany’s chemical weapons stock was seized by the allied forces. With this and the allied forces’ own stockpiles, amounting to vast amounts of toxic chemicals, Russia, Britain, France, and the USA opted for what seemed the easiest option: dumping much of it into the oceans. There were over 100 such dumps, totalling hundreds of thousands or perhaps even one million metric tonnes (Harigel, 2001; Curry, 2016). These vast dumps of containers of chemical weapons pose a significant risk to aquatic life and the environment (OSPAR, 2010).
Recent agreements
Despite the Geneva Protocol having had a positive effect on the use of chemical weaponry in warfare, the wording still left states free to develop, produce, and stockpile toxic and dangerous chemical weapons, including highly deadly nerve agents. However, the agreement did lay the foundation for future international agreements (as seen in figure 5). Drawn up in 1972, the Biological and Toxin Weapons Convention (BTWC) was the first agreement focused solely on the use of biological weapons, and it entered into force on 26th March 1975 (Arms Control Association (ACA), 2024; United Nations Office for Disarmament Affairs (UNODA), n.d. a). At the time of writing, 189 states were party to the agreement, although eight states have not yet ratified it (UNODA, n.d. b).
In 1993 there came the most comprehensive ban on chemical weapons yet, the Chemical Weapons Convention. This agreement, which includes the requirement to destroy chemical weapons and their production facilities, came into effect on 29th April 1997, and at the time of writing, 193 states were party to the agreement. Notably, four states are yet to fully join: Israel, Egypt, North Korea, and South Sudan (ICRC, n.d. g, n.d. h; Department for Energy and Net Zero (DESNZ), 2013; UNODA, n.d. c).
Figure 5 – Agreements on chemical and biological weapons after WWI
Effectiveness
Since the 1993 CWC treaty entered force in 1997, according to the OPCW (n.d. c), 100% of the declared world stock of chemical weapons has been destroyed. Despite this, there have still been instances of chemical weapon use, as shown in Figure 6, including use in terror attacks, civil wars, and occupations.
Figure 6 – Chemical weapons use after the CWC in 1993
Current
With social media, incidents in current conflicts are being broadcast live to thousands and sometimes even millions of viewers. This includes incidents of chemical weapons use in current conflicts, as well as many other atrocities.
Israeli forces have been reported to have used tear gases and white phosphorus against Palestinian and Lebanese civilians (Al Jazeera, 2023; Amnesty International, 2023; Al Jazeera English, 2024). White phosphorus, while not banned, is restricted under humanitarian law. It is indiscriminate, ignites in the presence of oxygen, is difficult to extinguish, and exposure can cause horrific injuries, death, or health problems (Amnesty International, 2023). The use of white phosphorus can also pollute rain, causing further risk to civilian populations, especially in places where people have little choice but to collect and drink polluted rainwater (Al Jazeera, 2023). Israel signed the CWC in 1993 but never ratified (ICRC, n.d. h).
In its offensive against Ukraine, Russia has been reported to have used chemical weapons on over 9000 occasions, including the use of tear gases, chloropicrin (a pesticide but also a choking agent), and white phosphorus (Spencer, 2025; Dols, 2025; PubChem, n.d. c). This has led to 2,500 injuries and at least three deaths, in a blatant violation of the CWC. Some states have reported Russia expanding its chemical weapon programme, although Russia denies this (Dols, 2025).
Other issues and the future
Chemical weapons are being used in conflicts around the world today , and their use has impacts beyond the immediately obvious. They can have wide-reaching environmental and human implications, and put ecosystems at risk, although this risk is difficult to quantify (Mayer & Johnstone, 1991). Most chemical weapons are indiscriminate and will destroy animals, plants, and humans. Some chemical weapons, or their degradation products, can pollute water and soils, further impacting the people and the environment. Some chemical agents persist in the environment, while others break down into other pollutants, some of which can cause further damage. Furthermore, the huge amounts of chemical weapons that were disposed of by dumping in the sea, or buried, could potentially have massive impacts on the ecosystems surrounding these dumps (OPCW, n.d. d).
Every ocean has had old chemical weapons dumped into its waters (OSPAR, 2010). Sea-dumped weapons pose long-term environmental and human risks, although these risks are largely unknown (Thomsen et al., 2010). While the long-term potential impact is hard to predict, sea-dumped weapons have already polluted the Baltic Sea’s underwater sediments. Dumped weapons also risk either being recovered and re-weaponised, or disturbed through human activity such as fishing, leading to potential release, which could further impact humans and ecosystems (Greenberg, 2015; Rapp Learn, 2020; Ajaykumar, 2025; Sanderson et. al., 2010). These, and buried chemical weapons, may need to be recovered for effective disposal, and to negate the risk of these weapons being recovered to be used (OPWC, n.d. d).
The implementation of the CWC is done by the OPWC, who oversee the declaration and verification of the safe destruction of chemical weapon stocks by parties to the CWC. The OPCW which states that 100% of the world's declared chemical stockpiles have been destroyed, although party states may still store any undeclared weapons, and some states have never signed or ratified the CWC (OPCW, n.d. c; OPCW n.d. d).
Chemical weapons have accounted for far fewer casualties of war than traditional artillery, but any weapon that causes death, horrific injuries and psychological damage, as well as damage to the environment, should be controlled.
The agreements on chemical weapons, particularly the almost unilateral CWC, have had a dramatic effect on global chemical weapons stores and use. However, accountability measures and repercussions for those states party to, and breaking, the agreement are still lacking.
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Bryony Maskell graduated from the University of Hull with an undergraduate master’s degree in chemistry and a postgraduate master’s degree in environmental change management and monitoring.
Image credit: Photo from chemical lab by Pavel Danilyuk via Pexels.Photo by Gustavo Martínez: https://www.pexels.com/photo/dark-tactical-figure-in-a-gas-mask-28830882/Photo by Gustavo Martínez: https://www.pexels.com/photo/dark-tactical-figure-in-a-gas-mask-28830882/
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