21
May
Fire Hazards and Toxic Combustion of Herbicide Products Increase Threats to Health and Environment
(Beyond Pesticides, May 21, 2025) An assessment of the fire hazards of four herbicide products in Science of The Total Environment finds high fire and toxic gas emission risk, particularly in 2,4-D-based weed killer products. The authors note that “Inert [nondisclosed] ingredients significantly influence flammability and toxic gas generation in fires,†and the combustion of these products “releases hazardous gases and polycyclic aromatic hydrocarbons.†These results highlight the fire hazards associated with herbicides, as well as the emission of hazardous substances into the atmosphere, which can threaten environmental and public health. Â
The authors summarize: “[T]he aim of this work is to raise awareness of the fire hazards posed by the storage of pesticides and what effect the ‘inert’ substances in them have. In the past, large fires have occurred around the world, e.g., in Basel (1986), Arkansas (1998), and in Eastern Virginia at the Bayer CropScience plant (2008). It is important to note that in addition to large factories and warehouses, fires can affect small crop protection product stores and local wholesalers.†(See related coverage on the 2023 train derailment, fire, and subsequent release of chemicals here.) The U.S. Fire Administration estimates 344,600 residential building fires nationally, based on 2023 data. A significant number of these residences will have stored and used herbicides on their property.
This research showcases how herbicides are capable of causing fire hazards, a safety consideration often disregarded when performing risk assessments. With both active ingredients and the inert components in the products affecting flammability and decomposition products, “a much wider range of toxic substances are produced during combustion and thermal decomposition, where often the active substance itself during combustion is the source of many toxic substances.â€
In analyzing herbicide products, which the study refers to as ‘plant protection products’ (PPPs), the researchers utilize four commercially available products containing two of the most commonly used active ingredients, glyphosate and 2,4-D. “Products differing in form and composition were selected in order to gain a broader understanding of the effects of inert ingredients on the flammability of plant protection products and the thermal decomposition and combustion products formed during their fire,†the authors explain.
Products 1 and 2 contain varying amounts of glyphosate (79% and 44%, respectively), with Product 3 as a mixture of glyphosate (27.9%) and 2,4-D (32%) and Product 4 containing 90% of 2,4-D. The focus of this study on herbicides is based on 2024 data from the Food and Agriculture Organisation of the United Nations (FAO), which shows that more than 50% of PPPs used are herbicides.
Glyphosate, an organophosphorus pesticide, is the most widely used herbicide, with 2,4-D also among the top herbicides utilized worldwide. 2,4-D, or 2,4-Dichlorophenoxyacetic acid, “is a compound in the synthetic auxin herbicides (SAHs) group that mimics the naturally occurring plant hormone, indole-3-acetic acid (IAA),†the researchers say. (See extensive Daily News coverage on these herbicides here and here.)
In the study, fire hazards are determined by analyzing combustible parameters tested on a cone calorimeter, which the authors describe as “one of the most widely used test apparatuses for determining the fire behaviour of materials.†Additional analysis includes the identification of thermal decomposition and combustion products, such as asphyxiating and irritant gases, hydrocarbons, and volatile organic compounds (VOCs).
“The analysis of gases produced during the combustion of PPPs—carbon dioxide (CO2), carbon monoxide (CO), hydrogen chloride (HCl), ammonia (NH3), formaldehyde (CH2O), nitrogen oxides (NOx), sulphur dioxide (SO2) and light hydrocarbons (methane (CH4), ethane (C2H6), propane (C3H8), ethylene (C2H4), and hexane (C6H14)—was carried out using a GASMET DX-4000, portable gas analyzer,†the researchers state, which “allows simultaneous measurement of chemical compounds present in exhaust gases.â€
From the flammability test, the authors note that the products containing 2,4-D ignited while the products with only glyphosate as the active ingredient did not. However, the researchers note that, “Toxic emission tests have shown that even products that do not ignite can undergo thermal degradation, which also results in the formation of large quantities of toxic substances.â€
Products 3 and 4, containing 2,4-D, also show serious fire hazards based on the reported calorimetric values, which were above 900 kW/m2 (kilowatts per square meter, a unit of measure to express power). “To give an idea of how much of a hazard the combustion of these materials causes, they achieve approximate values to materials such as automotive oil (600-1050 kW/m2), heptane (400-600 kW/m2) or diesel fuel (600-1400 kW/m2),†the authors emphasize.
For the identification and analysis of combustion products, the four herbicides were tested under two ventilation conditions within a steady state tube furnace. During this test, the products containing glyphosate also burned despite not igniting within the first test. The individual products emitted during the combustion of the samples shows that, “The largest amounts of carbon monoxide and carbon dioxide were detected in the gas mixture emitted during the decomposition of Product 3 and Product 4,†continuing, “Moreover, Product 3 emitted the largest amounts of hydrogen cyanide among all the studied PPPs.â€
The researchers continue: “In the gases released during the combustion of Product 4, which consisted mainly of the active substance 2,4-D, very large amounts of nitrogen dioxide, hydrogen chloride, and formaldehyde were also detected, especially when measurements were taken under oxygen-deficient conditions. Significant amounts of ammonia were also present in the fire effluents emitted during the decomposition of Product 1, which resulted from the breakdown of glyphosate-monoammonium, a component of this agent. The second product tested, based on glyphosate, contained glyphosate potassium.â€
The number of detected products in the gas samples are 18 (Product 1), 6 (Product 2), 37 (Product 3), and 29 (Product 4). Some of the identified products in Product 1 and 2 include aminomethanesulfonic acid, acetonitrile, pyridine, methylpyrazine, phenol, 4-pyridinecarbonitrile and 1H-pyrrole-2‑carbonitrile. “The gas mixture emitted by both Products 3 and 4 included hydrogen chloride, simple hydrocarbons such as benzene, toluene, styrene, benzofuran, substances belonging to polycyclic aromatic hydrocarbons (PAHs), chlorinated hydrocarbons, and chlorinated phenols,†the authors state.
They continue, noting that “chlorophenols can lead to severe health issues, including respiratory distress, skin irritation, and organ damage, especially in cases of prolonged exposure.†They add, “Moreover, some chlorophenols may have carcinogenic properties and can interfere with hormonal functions, potentially leading to conditions like cancer and reproductive issues.â€
The data show that Products 3 and 4 formed the largest amount of harmful hydrocarbons during decomposition, but also that all of the test products emitted methane, ethane, and ethylene. Since asphyxiating and irritating gases are the main cause of death during fires, these results are cause for concern, particularly for pesticide production and storage sites. (See here, here, and here.)
“It can be concluded from these results that, in addition to asphyxiating and irritant gases, many other toxic chemical compounds such as polycyclic aromatic hydrocarbons, benzene, phenols and their chlorinated analogues are formed during the combustion and thermal decomposition of PPPs,†the researchers conclude. “The presence of these substances in fire gases makes PPPs fires a hazard to the environment as well.â€
Previous research highlights the importance of considering both active and inert ingredients in risk assessments. Inert ingredients, which are undisclosed, can make up the majority of products and also be more toxic than the active ingredients. The authors share: “These inert ingredients should often be toxicologically neutral by design, but as it turns out, they often significantly affect the flammability parameters of PPPs and their combustion and thermal decomposition products. The presence of combustible components such as alcohols and natural oils can significantly influence their ability to ignite and create a hidden hazard in the occurrence of fires at PPP storage sites.â€
With both active and inert ingredients contributing to the combustion characteristics of pesticide products, substances can be formed during combustion that would otherwise not have been emitted with just the active ingredient. Since numerous facilities are involved in storing and processing pesticide products, the authors state: “Fires at these sites can produce substantial amounts of toxic combustion by-products. These by-products can spread through fire plumes, leading to severe airborne pollution that poses risks to firefighters and nearby residents.â€
The researchers continue by saying, “Additionally, firefighting runoff water, which may contain unburned pesticides and toxic substances, can contaminate surface and groundwater reservoirs, resulting in soil pollution.†(See study here and Daily News coverage on soil and water contamination here and here.)
In a previous Daily News, Beyond Pesticides highlights a study, published in the Journal of the American Heart Association, that finds a correlation between the number of fires fought annually and atrial fibrillation, one of the most common medical arrhythmias that increases the risk of stroke, heart failure, and other cardiovascular health issues. In the firefighting occupation, firefighters can experience exposure to chemicals and particulate matter in smoke, pollutants, volatile organic compounds, and polycyclic aromatic hydrocarbons that increase cardiovascular (heart) and respiratory distress risk through oxidative stress and autonomic function disruption. Considering firefighters live 10 to 15 years less than other occupational groups, studies like these are significant for understanding how chemical exposure contributes to health and wellness disparities.
A wide body of science demonstrates the harmful effects of pesticides on the environment and all organisms within it. The nation and world are currently experiencing multiple crises involving public health, climate change, and biodiversity that all are compounded by the toxic chemicals that are ubiquitous in the air, soil, water, and food we eat. The holistic solution for mitigating these effects lies in organic land management practices.
To learn more about the positive health and environmental effects of organic agriculture, see here and here. Interested in helping your community transition to organic? Become a Parks Advocate through the Parks for a Sustainable Future program. Make your voice heard by taking action to Tell Members of Congress To Cosponsor Bills Supporting Organic Agriculture and stay informed by signing up for Action of the Week alerts to be delivered straight to your inbox.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Przybysz, J. et al. (2025) Assessing fire hazards of herbicides: Identifying toxic emissions from pesticide combustion, Science of The Total Environment. Available at: https://www.sciencedirect.com/science/article/pii/S0048969725011829.
