The Most Dangerous Chemical in My Lab... and it's Not What You Think!

The Most Dangerous Chemical in y Lab

It's not what you think! 

I’m March for Science – Seattle’s resident chemist and a certified lab rat. The single most important part of my job is to ensure the health and safety of the students in my upper division chemistry labs. I work closely with undergraduates and I often get asked, “What is the most dangerous chemical that you’ve ever worked with.” After much thought, my answer surprises most people because it’s not what you think! When I think about chemical safety there are three important considerations: acute toxicity, persistence, and reliability.

Eric Camp performing a chemistry demonstration. This specific demosration involves igniting a balloon filled with hydrogen. This produces a small explosion. 

Eric Camp performing a chemistry demonstration. This specific demosration involves igniting a balloon filled with hydrogen. This produces a small explosion. 


1.       Acute Toxicity: This is an official OSHA term for the immediate (up to two weeks) health effects resulting from a single exposure. It all boils down to, “If I inhale it, ingest it, touch it, will it hurt me?” In my lab I use a lot of concentrated hydrochloric acid (Conc HCl). This compound definitely meets the criteria of “Acutely Toxic”. One unique characteristic of Conc HCl is that you can simultaneously inhale, ingest, and touch it with a single exposure. Some folks say that Conc HCl smells bad; I disagree. It smells irritating. I make the distinction because when HCl contacts the mucosal lining of the sinuses it reacts with water and turns into an acid. The bad smell is really a chemical burn. Whereas Conc HCl has a high risk of acute toxicity – specifically chemical burns -- it is not a chemical that will persist in the environment for a long duration. It also has a well-documented and reliable chemical behavior. While Conc HCl is a dangerous compound and should be handled with care, in my opinion, it is nowhere close to dangerous enough to top my list.

2.       Persistence:  Our body does a pretty good job removing unwanted agents from our system, thank you, liver!  “Persistent adverse health effects” indicates how long the effects of exposure take. HCl will burn on contact, then it is done. Not persistent. Other compounds, however, can remain in the body or in the environment for prolonged periods. One class of chemicals that would be rated high on this list would be mercury compounds. Dimethylmercury is one of the most dangerous chemicals on earth. In a very famous incident, chemist Karen Wetterhahn spilled a drop of this mercury compound on her gloved hand. She then removed the glove and went on with her day, but the compound had penetrated the glove. Ten months later she died of mercury toxicity. While this compound meets the criteria for acute toxicity and persistence, I have never encountered this particular chemical. I have, however, seen plenty of organo-mercury compounds. Because of stories like this and the risk of environment persistence and the influence of the emerging field of Green Chemistry, mercury compounds are avoided whenever possible.

3.       Reliability: This defines whether a chemical will behave in a way that is easy to predict. When handling chemicals, I like them to be reliable. It all comes down to being able to predict when a reaction will happen and how quickly it will occur. Thermite is a great example of this. When ignited, thermite burns hot and makes an impressive fiery display. However, thermite will sit on a shelf for eternity and will not combust. When I drop a burning magnesium strip into it, providing the needed activation energy, it will burn white-hot for 10 seconds and extinguish itself. I have safety precautions in place but as long as I follow them, I am fine. Ethers, on the other hand, are not reliable. The most famous ether, diethyl ether, was used as an anesthetic during the 19th century. It has two unreliable components. First, it is very flammable. It has a very high vapor pressure, which means it’s very volatile and turns into a gas easily. Click here to watch a video of a combustion reaction using ether. As a chemist, I only handle diethyl ether in a fume hood, which removes the flammable gas. The second concern is that ethers will form peroxides over time. These peroxides crystalize and become a contact explosive. Any old bottle of ether should be considered a live bomb. Simply moving a bottle of ether with peroxides could result in detonation, igniting the ether itself. Any ether older than six months should be considered a hazard. Click here to watch a bomb squad decontaminate an old ether bottle found in a storage locker. 

Using these criteria of acute toxicity, persistence, and reliability, a compound such as dimethylmercury would be at the top of my list, yet I’ve never encountered it. There is one compound that I have encountered and is nearly as toxic, persistent, and very unreliable.  In my graduate studies I studied organometallic chemistry (attaching organic compounds to metals). My protocol required me to make a carbonylate a compound. This involved blowing pure carbon monoxide (100% concentration) into a reaction flask for a prolonged period of time. I remember one specific day at the lab, the clamp holding the rubber tubing connecting the tank of carbon monoxide failed and the tube started flailing and filled the lab with CO. Thankfully I used my safety training. Holding my breath, I turned off the gas and immediately left the area. 

Acute Toxicity: 1 breath of 2% CO will kill you in three minutes. 

Persistence:  low-level chronic exposure (0.0035%) leads to significantly shorter life due to heart and nerve damage

Reliability:  It’s certainly reliably deadly, but more worrisome is that it is a colorless gas with no odor. You simply cannot see it or smell it. In the US alone, 15,000 people visit the emergency room annually due to CO poisoning and of these 500 people die. You cannot rely on a compound you cannot sense.

When I talk with my students about my most feared chemicals they are often surprised, because they are, “old school chemicals”. They are things that everyone knows can hurt or kill you. The simple fact is that these chemicals have a reputation for a very good reason. As the field of chemistry moves forward, we shy away from creating new persistent, acutely toxic, and unpredictable compounds, because we know what the consequences will be.

A robustly funded EPA that publically communicates their data and science helps make us safer as a community. They help identify new potential toxins and carcinogens and regulate their removal from the industrial and agricultural industry. As a result, the majority of the chemicals that you will find under your sink are relatively safe if you use them according to the directions. Our lives are better because of chemistry, we just need to carefully read the instructions and respect the safety protocols.


About the Author: This weeks blog was athored by March for Science - Seattle's resident chemist Eric Camp. Eric works for the University of Washington and manages the upper division chemistry labs.