Vinyl chloride comes primarily from industrial manufacturing, where it serves as the building block for PVC plastic. Nearly all vinyl chloride produced in the United States goes directly into making polyvinyl chloride, the material behind plastic pipes, wire coatings, packaging, vinyl siding, furniture upholstery, and automotive parts. But vinyl chloride also shows up in the environment through less obvious routes: the breakdown of other chemical pollutants in groundwater, emissions from landfills, and even trace amounts from volcanic activity.
How Vinyl Chloride Is Made Industrially
The vast majority of vinyl chloride is synthesized from ethylene, a gas derived from petroleum and natural gas processing. The production happens in two stages. First, ethylene reacts with chlorine to create an intermediate chemical called ethylene dichloride. Then that intermediate is heated until it “cracks” apart into vinyl chloride and hydrogen chloride gas. The hydrogen chloride byproduct doesn’t go to waste. It gets recycled back into the process through a second reaction pathway called oxychlorination, where it combines with more ethylene to produce additional ethylene dichloride, keeping the cycle going.
There’s also an older production method that starts with acetylene instead of ethylene. This route is rarely used in the West but remains significant in China, where roughly 70% of vinyl chloride production relies on acetylene-based chemistry. That process requires mercury as a catalyst, which is one reason international agreements have pushed for its phase-out.
PVC: Where Nearly All of It Ends Up
Since the mid-1970s, vinyl chloride has been used almost exclusively to make PVC. Before that, it had a surprisingly wide range of consumer applications. It was used as a refrigerant, as a propellant in aerosol spray cans, and even as an ingredient in some cosmetics. Once its health risks became clear, those uses were abandoned, and today the chemical exists mainly as a raw material that gets locked into the polymer chain of PVC plastic.
The scale of production is enormous. An estimated 1.5 billion pounds of vinyl chloride travels by rail each year in the United States alone, carried on roughly 8,595 rail cars from production facilities to plastics plants. At any given moment, up to 36 million pounds may be in transit across nearly 2,000 miles of railways.
Groundwater Contamination From Solvent Breakdown
One of the most important sources of vinyl chloride in the environment has nothing to do with vinyl chloride production itself. It forms underground when common industrial solvents break down. Tetrachloroethylene (often called PCE or “perc,” the chemical used in dry cleaning) and trichloroethylene (TCE, widely used as a metal degreaser) are among the most frequent groundwater contaminants in the country. When bacteria in oxygen-poor soil and aquifers encounter these chemicals, they strip away chlorine atoms one at a time in a process called reductive dehalogenation.
The sequence works like this: PCE loses a chlorine atom and becomes TCE. TCE loses another and becomes dichloroethylene. Dichloroethylene loses yet another and becomes vinyl chloride. Under ideal conditions, bacteria can eventually break vinyl chloride down all the way to carbon dioxide, but that final step is often the slowest. This means vinyl chloride can accumulate in groundwater at sites contaminated with PCE or TCE, sometimes persisting for years at concentrations that matter for health. The EPA’s maximum contaminant level for vinyl chloride in drinking water is just 0.002 milligrams per liter, or 2 parts per billion, reflecting its cancer risk even at low levels.
Landfill Gas and Atmospheric Sources
Landfills are another source. As buried waste decomposes, it generates gas containing a mix of volatile organic compounds, including vinyl chloride. EPA monitoring data from closed and abandoned landfills shows typical vinyl chloride concentrations in landfill gas ranging from less than 1 part per million to a default estimate of about 7 parts per million, with some sites reaching nearly 19 parts per million at the 90th percentile. These concentrations vary widely depending on what was buried and how the site is managed.
Vinyl chloride can also leach into drinking water from the very product it’s used to make. PVC pipes, particularly older ones manufactured before modern quality controls, can release trace amounts of unreacted vinyl chloride monomer into the water flowing through them. The EPA specifically lists “leaching from PVC pipes” alongside “discharge from plastic factories” as sources of vinyl chloride in drinking water systems.
In the atmosphere, vinyl chloride doesn’t linger. Sunlight triggers reactions with hydroxyl radicals that break the molecule down, giving it an atmospheric half-life of roughly 18 hours under typical conditions. In smoggy, high-pollution environments where nitrogen oxide levels are elevated, that half-life can drop to as little as 1 to 4 hours. So airborne vinyl chloride from industrial emissions, landfills, or accidental releases tends to degrade within a couple of days rather than building up over time.
Natural Sources
Vinyl chloride does occur naturally, though in quantities that are tiny compared to industrial production. Researchers have documented its presence in volcanic fumarole emissions, including from Mt. Etna and Vulcano Island in Sicily, where it appears alongside other chlorine-containing organic compounds. A 2002 study published in Environmental Science and Technology also identified natural formation of vinyl chloride in terrestrial environments, likely through geochemical reactions involving organic matter and chlorine in soil. These natural sources contribute trace amounts to the global budget of the chemical but aren’t considered a meaningful exposure risk.
Workplace and Community Exposure
For workers in PVC manufacturing and vinyl chloride production facilities, inhalation is the primary exposure concern. OSHA sets the permissible exposure limit at 1 part per million averaged over an 8-hour shift. That limit reflects decades of evidence linking chronic vinyl chloride inhalation to a rare liver cancer called angiosarcoma, along with other liver damage.
Communities near production plants, along rail transport corridors, and above contaminated groundwater plumes face different exposure pathways. The 2023 train derailment in East Palestine, Ohio brought national attention to the risks of rail transport, but the underlying concern isn’t new. Vinyl chloride has been a regulated hazardous air pollutant and water contaminant for decades precisely because it enters the environment through so many routes: factory emissions, groundwater solvent degradation, landfill gas, aging PVC infrastructure, and the sheer volume of material moving across the country by rail every day.