Earlier this month, a train derailment in Ohio caused a number of chemicals to be released into the environment. Those chemicals included 3 monomers; vinyl chloride, butyl acrylate, and ethyl hexyl acrylate that are used to make materials ranging from pipes to adhesives. These monomers (like most vinyl monomers and acrylates) do pose health risks, are irritants, and depending on exposure levels and durations can cause cancer, vinyl chloride being the most toxic of these chemicals. Already there have been reports of many dead fish in the vicinity of the train incident. Although the East Palestine derailment is making a lot of news, vinyl chloride releases to the environment are unfortunately not so uncommon; according to the EPA’s Toxic Release Inventory over 400,000 pounds of vinyl chloride were released in the US in 2021 based on 38 manufacturing facilities in 15 states. In 2021 the largest emitter of vinyl chloride was Formosa Plastics Corp. Texas, which released 68,000 pounds of vinyl chloride into the air.
The response to this disaster has included a controlled burn of at least some of the released chemicals. This choice can be understood when considering the physical properties of vinyl chloride, which include;
Boiling point: -13.4 deg. C (7.9 deg. F)
Flash point temperature: -78 deg. C (-108.4 deg. F)
Lower flammable limit: 3.8 vol. %
Upper flammable limit: 29.3 vol. %
Vapor density: 2.2 times more than air.
Vapor pressure: 2580 mm. of mercury at 20 °C (68 °F) – 49.9 psi
These monomers are transported as liquids, the vapor pressure of vinyl chloride keeping it as a liquid in the train car. Vinyl chloride will sink and form a cloud on the ground in its gas form. If a hole were to be drilled in the tipped train car it would reduce the pressure, thereby causing it to boil and releasing a lot of vapor into the environment. Burning the vinyl chloride results in CO2 and HCl gases, possibly some phosgene as well (COCl2). Given these realities of the situation, a controlled burn was likely the best way to reduce the chances of vinyl chloride persisting in the environment.
This train derailment is one notable example, but plastics and plastics related waste are a persistent environmental problem. As mentioned, a good deal of vinyl chloride is regularly released into the environment. Phthlates and other chemicals used as plasticizers or other additives can diffuse out of solid waste, and microplastics are increasingly omnipresent (even in human beings). As we move forward to solve the plastic waste problem, consideration must be given to these environmental releases of small molecules associated with plastics as well.