Chloropicrin: Everything old (in CBRN) is new again

Tactical CBRN

Chloropicrin (NATO code PS) was first used as a chemical warfare agent by Russia in 1916 during WWI. It's relevant again today.

BLUF:

On a spectrum of severe effects, chloropicrin toxicity falls between chlorine and phosgene but also has GI symptoms. Ocular and direct skin exposure can resemble sulfur mustard contact.

Researched and written by Mike Shertz, MD/18D, not AI

🕖 Reading Time, 4 minutes

Later in WWI, allied forces also used Chloropicrin.¹ More recently, Russia has likely been using it against Ukraine. See, the Wall Street Journal article from May 23, 2024: “Burning Skin, Teary Eyes: Ukraine’s Trops Say Russis is Using a Banned Toxic Gas. Ukrainian forces describe the physical effects of gas they say Moscow’s troops are using to oust them from their positions.”

Interestingly, 3.4% of Ukrainian drone-injured casualties had some toxic exposure, generally felt to be chloropicrin from Russian K-51 grenades. (Originally published online by Noble Slave – Military Medicine in the Armed Forces of Ukraine, but no longer available).

Civilian Use: Chloropicrin is also used in houses undergoing fumigation to deter human entry and subsequent exposure to the fumigating agents (because although the fumigants are largely undetectable, the chloropicrin is not). In 2015 and 2017, an organized crime group intentionally released chloropicrin in nightclubs in Honolulu, Hawaii. They did so in order to drive patrons away from a competitor’s business and toward the organized crime group’s own nightclubs. Apparently, the crime group also owned a pest control company, so the choice to use chloropicrin was simply for convenience and availability.²

Cloropicrin Background

Chloropicrin is a colorless-to-faint-yellow liquid with a highly irritating odor. Historically described as smelling like “fly paper,” it was first patented in 1908 as an insecticide.

In the 1950s, it was a common soil fumigant, able to kill fungus and other parasites.³ It is currently a restricted-use pesticide in the US, but at one time, it was the 4th most common insecticide in the USA and was frequently used in Japan as well. ⁴ Despite its long history of use, little actual human clinical data exists. Most involve experimental animals or accidental human exposures as a fumigant.

Its high volatility causes it to dissipate rapidly in the environment. Low water solubility mainly results in central airway and mucus membrane effects.³

Chloropicrin Classification

Although often described as a “tear gas or harassing agent,” it is more appropriately classified as a pulmonary / choking / or irritating gas. As the agent decomposes in the environment, it degrades to chlorine and phosgene gases, both of which are more common and are traditional pulmonary agents. ⁵ Another aspect of its low water solubility is potential groundwater contamination for up to 30 hours. ⁶ Its use during WWI was often as a “vomiting agent” because it could penetrate through early protective masks and cause vomiting.* This resulted in soldiers removing their protective masks to vomit, thereby greatly increasing exposure to the agent. ³

Clinical Presentation

In a review of over 600 accidental exposures, 65 to 93% had ocular symptoms, 45 to 54% respiratory, and 19 to 47% systemic complaints. ⁶ Immediate low-level exposure results in watery eyes, runny nose, and cough from mucus membrane and upper respiratory tract irritation ⁶ This seems consistent with other traditional “riot control agents” like CS. Ocular exposure can result in eyelid swelling and corneal ulceration by 24 hours, much slower than vesicants (i.e., sulfur mustard and lewisite). Unlike those later agents, recurrent corneal ulceration hasn’t been reported. Vesicants are known to cause corneal opacification, which can occur with chloropicrin as well, but generally takes 3 to 7 days, as opposed to hours with mustard and lewisite. ³

Oddly, hyphemia, blood pooling in the anterior chamber of the eye with gravity has been reported in mice exposed to chloropicrin, but it didn’t occur until day 25 post-exposure, which hasn’t been seen with the other agents. This can result in increased intraocular pressure and retinal damage. Currently, there is no specific ocular treatment for chloropicrin toxicity. ⁴

With increasing dose or prolonged exposure (likely because chloropicrin breakdown products include both chlorine and phosgene), death can occur from pulmonary edema. Methemoglobinemia can occur, but how it occurs is poorly understood. ^3,6

Taken together, this is often called “PS syndrome”: eyes, nose, throat irritation, headache, nausea, vomiting, and shortness of breath both from lung irritation, subsequent decreased respiratory rate, and pulmonary edema. ³

Direct skin contact results in itching, irritation, rash, and blistering ³ which could be confused with sulfur mustard exposure.

*Current US DOD CBRN protective mask filters are able to filter out this agent.

Notes

¹Henderson, Terry J., Chemistries of Chemical Warfare Agents. Chemical Warfare Agents, 3^rd Ed, Editors, Brian J. Lukey, James A. Romano, Jr., Harry Salem. CRC Press, 2019.

²Tropical Nights, Burning Eyes: Chloropicrin in Hawaii, By Markus K. Binder, published by CBNW,

³Salem, Harry, Riot Control Agents. Medical Aspects of Chemical Warfare, 2^nd Ed, Editor Tuorinsky, Shirley. Borden Institute, 2008.

⁴Okoyeocha EOM, Tewari-Singh N. Chloropicrin induced ocular injury: Biomarkers, potential mechanisms, and treatments. Toxicol Lett. 2024 May 15;396:70-80. doi: 10.1016/j.toxlet.2024.04.006. Epub 2024 Apr 25. PMID: 38677567.

⁵Marzec J, Nadadur S. Countermeasures against Pulmonary Threat Agents. J Pharmacol Exp Ther. 2024 Jan 17;388(2):560-567. doi: 10.1124/jpet.123.001822. PMID: 37863486; PMCID: PMC10801713.

⁶Pesonen M, Vähäkangas K. Chloropicrin-induced toxicity in the respiratory system. Toxicol Lett. 2020 May 1;323:10-18. doi: 10.1016/j.toxlet.2020.01.022. Epub 2020 Jan 23. PMID: 31982502.

Mike Shertz MD/18D

Dr. Mike Shertz is the Owner and Lead Instructor at Crisis Medicine. Dr. Shertz is a dual-boarded Emergency Medicine and EMS physician, having spent over 30 years gaining the experience and insight to create and provide his comprehensive, science-informed, training to better prepare everyday citizens, law enforcement, EMS, and the military to manage casualties and wounded in high-risk environments. Drawing on his prior experience as an Army Special Forces medic (18D), two decades as an armed, embedded tactical medic on a regional SWAT team, and as a Fire Service and EMS medical director. Using a combination of current and historical events, Dr. Shertz’s lectures include relevant, illustrative photos, as well as hands-on demonstrations to demystify the how, why, when to use each emergency medical procedure you need to become a Force Multiplier for Good.

Chloropicrin (NATO code PS) was first used as a chemical warfare agent by Russia in 1916 during WWI. It's relevant again today.