It’s easy to conjure up images of terrifying substances. Botulinum toxin, a bacterial poison, reigns supreme as the most toxic naturally occurring compound on Earth. Similarly, VX, a potent nerve agent developed as a chemical weapon by the British military, is equally fearsome. Chlorine trifluoride, an ultracorrosive, colorless gas, is so reactive it can ignite materials like water, sand, and even the ashes of substances that have already burned. With such diabolical possibilities, the question arises: which chemical poses the greatest danger? The answer hinges on a combination of effect and exposure – how much is lethal, and what exactly will it do to you?
Nerve agents are widely considered the most toxic chemical weapons due to their minuscule toxic limits and devastatingly rapid effects on the human body. A mere 10 milligrams (one ten-thousandth of a gram) of VX can cause death within minutes. However, only one fatality from VX has been recorded over the past decade. Conversely, over 100,000 people in the US suffer accidental poisoning each year from common household chemicals like bleach and disinfectant, despite these substances being slower-acting and far less toxic than VX. Furthermore, combining certain common chemicals can be fatal. For example, mixing drain cleaner and bleach releases poisonous chlorine gas.
These two examples highlight a critical aspect of ranking chemical danger: to assess danger, you need to understand the likelihood of encountering the chemical. Safety professionals define danger using a combination of hazard and risk. “A hazard is something with the potential to cause harm. Risk is the likelihood that harm will arise and the severity of that harm,” explains Dr. Webb, the health, safety, environment, and well-being officer at the University of Cardiff’s School of Chemistry. The hazard is an intrinsic property of a tool or chemical, whereas risk fluctuates depending on its use.
We instinctively consider this balance of factors daily. Take a kitchen knife: we know the blade is sharp and capable of cutting, including us, under the right circumstances. However, how we use and store the knife determines whether it poses a danger to us, Webb notes. This same logic applies to chemicals. “Even a very hazardous chemical does not pose any risk if there is no exposure,” states a spokesperson for the Finnish-based company. Therefore, while botulinum toxin, VX, and chlorine trifluoride are extremely hazardous, their risk to the average person is very low.
“Some hazardous chemicals are also essential for our health in small doses,” adds the spokesperson, “whereas in higher exposures, they may be lethal.” Ordinary table salt is a prime example. The small amount we consume in our diet is vital for maintaining the correct ion balance within our bodies, but excessive intake can lead to severe health problems, such as hypertension and kidney failure. Outside the body, large quantities of the same salt act as a potent herbicide by overwhelming plants’ ion balance to the point of death.
Even determining which chemicals are the most hazardous is a challenging endeavor, given the myriad ways they can cause harm. The European Union’s classification, labeling, and packaging regulations define various hazard categories, including toxic, explosive, and corrosive. However, Webb emphasizes that the most dangerous category depends on the context. For instance, although chlorine is a common pool disinfectant today, its concentrated gas form was once used as a chemical weapon, causing both chemical burns and respiratory irritation. The key difference, however, is that pools contain only a small amount of chlorine, and this small amount is dissolved in water. “The thing that makes it high risk is the fact it’s a gas,” Webb explains.
On paper, cyanide looks much worse. “It’s famously poisonous. It binds to your hemoglobin permanently, which stops it from carrying oxygen so you can’t respire,” Webb says. However, as a solid, it’s much easier to handle, meaning scientists working with this toxic compound can more readily avoid exposure to its nasty effects. “If you work with it safely – you wear your PPE [personal protective equipment], work in a fume hood, and wash your hands when you finish – the likelihood of contaminating yourself is pretty low,” Webb explains. This highlights that our safety is often within our own control.
Anything can become dangerous if mishandled, but there are steps we can take to mitigate the likelihood of harm. “The most important thing is knowing exactly what the hazards are and what you can do to minimize the risk,” Webb concludes.
