Mad About Science: Vinyl Chloride

By Brenden Bobby
Reader Columnist

In the wake of the Norfolk Southern train derailment in East Palestine, Ohio, on Feb. 3, a substance called vinyl chloride has been making headlines and appearing all over social media feeds. What is vinyl chloride, is it safe and what are the potential environmental impacts of the train derailment?

Answering all of these questions with absolute certainty is nearly impossible, but there are a few things that we do know.

What is vinyl chloride? It is a manufactured colorless gas used in the production of polyvinyl chloride, or PVC — a type of plastic you’ve likely seen most commonly in the form of white or pastel-green water pipes. PVC has an immense number of uses, ranging from water pipes to catheter tubes. PVC isn’t a known human carcinogen and has even been safely applied to things like food trays. The safety of this material only applies after polymerization, however, once vinyl chloride has been processed and manufactured into polyvinyl chloride.

Before polymerization, vinyl chloride exists as either a gas or liquid at extremely low temperatures. Vinyl chloride monomer, often referred to as VCM or chloroethene, is an extremely flammable and carcinogenic material with effects on biological anatomy that haven’t been fully explored and are still not completely understood.

VCM exists as a volatile liquid below 7 degrees Fahrenheit or under immense pressure. This means that it will transfer back into a gas with an explosive force, making it extremely flammable — especially when its container is compromised. A number of fail-safes are in place to contain vinyl chloride during storage and transportation. It is contained in a set of two pressurized spheres when it’s stationary, with a buffer zone between the spheres lined with detectors to monitor whether any of the substance is leaking into the buffer zone. If it is, it’s pumped into a subterranean storage area until the leak can be safely addressed.

During rail transportation, it is transported in large black pill-shaped chemical rail cars. These rail cars carry a vast array of different chemicals, while some are even left intentionally empty to ensure identifying the substance within is virtually impossible without proper authorization. The thought behind this is that it will help minimize the chance of theft or domestic terrorism — if bad guys can’t easily target highly explosive rail cars, they’re less likely to do irreparable harm to communities and the environment. It’s similar to setting a box full of dog poop outside to punish potential porch pirates.

Aside from its explosive volatility, the biggest threat of vinyl chloride is through inhalation. An extremely small amount of VCM — as little as 500 parts per million in breathable air — will begin to cause symptoms. The more vinyl chloride that is inhaled, the more rapid and enduring the symptoms of its exposure become. 

Inhaling vinyl chloride causes a number of symptoms, including weakness; abdominal pain; gastrointestinal bleeding; acrocyanosis (the effect of your extremities becoming pale-bluish, as though you’ve been exposed to extremely cold air, due to constriction of the blood vessels and lack of oxygen); and a particularly aggressive form of liver cancer. Contact with the liquid form of vinyl chloride will cause immediate frostbite.

Despite vinyl chloride evaporating into a gas at a very low temperature, it’s possible for large amounts of it to contaminate a water supply. This can wreak havoc on local ecosystems as well as human communities. As it enters the environment — such as after a train car full of it derails and breaks open — some of it leaches into underground water sources. The bulk of it may have exploded or evaporated at the crash site, but very large amounts can still spill into the environment and cause problems. This contaminated water is sucked up by human wells and water systems and enters human homes and businesses, where it is released into the air in its gaseous form, causing the aforementioned symptoms if it is present in a sufficient enough quantity.

There is extremely limited information about how this substance behaves after contaminating an ecosystem — particularly its effect on aquatic wildlife — but it’s widely accepted that it’s extremely lethal to anything that breathes it in, whether that’s through the creature’s skin, gills or lungs. Vinyl chloride exposed to open air generally evaporates over the course of several hours, unless the temperature is extremely low. It persists longer in water, especially if it leaches into subterranean aquifers or water systems for humans. VCM will break down naturally, but it will form other carcinogenic compounds like formaldehyde as it does so.

This substance has also been observed to reduce sex drive in men and shrink the testes of male animals that are exposed to it for a long period of time. Women who have been exposed to it for extended periods have had irregular menstruation periods. People who actively worked in plants that produce PVC plastics have sometimes experienced a deterioration of the bones at the very ends of their fingers, which seems to be linked to the same blood flow restriction that causes acrocyanosis.

There is a tiny amount of vinyl chloride in the air around us at all times. This is caused by a number of factors, from microscopic amounts breaking off from everyday PVC items, to our proximity to landfills or chemical plants. In very small amounts, our liver is able to filter out the compound with absolutely no adverse effects, but large quantities and extended exposure is almost certain to cause severe long-term effects. As cigarette smoke also produces vinyl chloride, your exposure to this compound goes up significantly if you, or someone close to you is a smoker.

Stay curious, 7B.