The pattern is depressingly familiar by now: a Black man dies at the hands of police; the entire nation bears witness through social media; protests sweep the nation crying out at this injustice and the systemic issues that guarantee similar deaths to come—and demonstrators are met with tear gas in a show of the very sort of violence they are protesting.

It’s shocking enough to watch this unfold on a screen, but it’s entirely different to witness the community trauma, the anger, the grief firsthand. We are Ph.D. students in Minneapolis, and while we were outraged for Michael Brown and devastated for Tamir Rice—among many, many others—it wasn’t until last summer that we saw armored National Guard vehicles drive down the streets of our own city during the protests against the killing of George Floyd. They have been reignited following the killing of Daunte Wright in neighboring Brooklyn Center, as Derek Chauvin’s murder trial proceeded here. These events have been marked by widespread use of tear gas against crowds of often peaceful protesters. But what do we really know about the long-term health and environmental effects of these chemical weapons? 

After those first frantic nights when our labs were closed down—when we could hear helicopters circling over our homes and see smoke rising from the 3rd Police Precinct building—we were expected to go back to life as usual: get to campus, do our research and return home to watch the news anxiously. We are each passionate about our individual research—on neurodegenerative diseases, on the role of kidneys in hypertension, on how stress accelerates aging, on the development of the nervous system and the neural circuitry underlying social behavior—but it was difficult to focus on these projects when police and protestors clashed every night.  

Shocked by the sheer volume of tear gas and the indiscriminate threat to peaceful protests during a respiratory-disease pandemic, we used our research training to investigate this form of "less lethal" crowd control. However, after digging into historical, legislative and scientific sources, we realized that the reassuring description of these weapons covers up a much more alarming story. We used peer-reviewed scientific articles, news sources and legislative documents to research the health and environmental effects of tear gas and the policies that govern its use. What we found was a long history of graft and greed, propaganda and paid publicity, and racism and regulatory gaps—all underscored by a lack of rigorous scientific research. 

Originally created during World War I as a battlefield weapon, tear gas was prohibited for use in war by both the Geneva Protocol and Chemical Weapons Convention. Following the ratification of the Geneva Protocol in 1925, the U.S. military was left with a stockpile of chemical weapons but no place to use them. General Amos Fries decided to make use of this cache by selling it to private security forces and police departments across the country, while maintaining close ties to one of the tear gas manufacturers. Police throughout the country started using these chemicals, swayed by propaganda campaigns encouraged by Fries and his team of lawyers, marketers and scientists. It quickly became the “humane” alternative for police and private security forces to use for crowd dispersal. The rhetoric initially employed to encourage tear gas use was suffused with white supremacist language, which likely contributed to its aggressive use against civil rights protestors in the 1960s. It also might help explain why tear gas is used more often on left-leaning protesters than right-leaning protestors. 

The use of tear gas to suppress protests for social justice is exactly what we have seen in our Twin Cities community. Following the killing of Daunte Wright, police shot tear gas and rubber bullets at a crowd gathered across the street in front of several apartment buildings. Some of that tear gas entered those apartments; the apartments of people who have had no choice but to bear witness night after night, as protestors called for justice in front of the air freshener–festooned barricade surrounding the Brooklyn Center Police Department.

Not only is tear gas an indiscriminate weapon, affecting protestors and bystanders alike, but very little is known about its long-term effects on human health and the environment. While the short-term exposure effects—difficulty breathing, coughing, crying, redness—are well established, many studies stop monitoring symptoms after a few hours. This is problematic, because one study in monkeys and two studies in humans indicate that some health effects don’t emerge until 12 hours after exposure. Early animal studies were conducted to discover the doses at which tear gas exposure was lethal; they were not done with the intention of monitoring the long-term health effects. This means we have a good idea of how much tear gas it would take to immediately kill a person, but little idea of what the effects of exposure to lower concentrations, like those used on protestors, may ultimately be. 

Perhaps most shocking of all is the stark lack of governmental oversight. We were not able to clarify which federal agency regulates tear gas manufacturing or use. None of the expected agencies (EPA, FDA, CDC or Bureau of Alcohol, Tobacco, Firearms and Explosives) claims oversight. The EPA only sets “acute exposure guideline levels for airborne chemicals” (AEGLs) to describe the health effects of exposure to certain chemicals. CS gas (one of the most common tear gases) has no concentration that can be considered less than AEGL level 2, described as “Irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape.” Given this classification, it is shocking that the government does not regulate these chemicals or their use. In a country where the size of your soda can be regulated, how have these chemicals slipped through? 

The Geneva Protocol exception for the domestic use of tear gas specifies that any chemicals used on civilians must have effects that “disappear within a short time.” Can tear gas really fall under this provision when there is evidence that its effects are not necessarily short-lived? How is continuing to use these chemicals different from uncontrolled testing on the human population? How can we justify the use of these chemical weapons on civilians, especially when we acknowledge their racist roots in policing? Our conclusion is that we can’t. The terms “safe” and “nonlethal” are misleading in the context of tear gas. The relationship between law enforcement and civilians needs to change, and we can start by reevaluating why weapons that are banned in war are nonetheless used on civilians. 

We hope the Twin Cities, which has been the center of so much pain and strife, can be at the forefront of a new social movement: one that campaigns for laws banning the use of tear gas against civilians.