Chlorinated solvents are a family of industrial chemicals made by attaching chlorine atoms to simple hydrocarbon molecules. They’re powerful degreasers and cleaning agents, widely used in metal cleaning, dry cleaning, and manufacturing of plastics, lacquers, and PVC products. They also happen to be among the most common groundwater contaminants in the developed world, and several are classified as known or probable human carcinogens.
The Four Chemical Categories
Chlorinated solvents are grouped into four categories based on their underlying molecular structure. The simplest are the chlorinated methanes, built on a single carbon atom. This group includes carbon tetrachloride, chloroform, and methylene chloride. Chlorinated ethanes have a two-carbon backbone with a single bond between them and include 1,1,1-trichloroethane (TCA), once one of the most popular industrial degreasers. Chlorinated ethylenes also have two carbons, but connected by a double bond. This category contains the two most notorious members of the family: trichloroethylene (TCE) and tetrachloroethylene, commonly called perchloroethylene or “PERC.” The fourth group, chlorinated benzenes, is built on a six-carbon ring structure and includes chlorobenzene and dichlorobenzene.
What these chemicals share is the ability to dissolve oils, greases, and waxes quickly without catching fire. Unlike petroleum-based solvents, most chlorinated solvents are nonflammable, which made them attractive for use around welding, machining, and other heat-generating industrial processes.
Where They’ve Been Used
TCE became the go-to degreaser for metal parts in manufacturing, aerospace, and electronics. It was also used to remove caffeine from coffee beans in the production of decaffeinated coffee and even served as an anesthetic gas in hospitals. PERC dominated the dry cleaning industry for decades and remains in use at many facilities today. Methylene chloride has been widely used as a paint stripper and in pharmaceutical manufacturing. Carbon tetrachloride, once common in fire extinguishers and as a cleaning agent, was phased out of most consumer uses years ago but persists as an environmental contaminant.
The common thread is that these solvents entered the environment through evaporation, leaks, and improper disposal. Factories, military bases, and dry cleaning shops are the most frequent sources of contamination at cleanup sites across the country.
Health Risks of Exposure
Occupational exposure to chlorinated solvents has been linked to damage affecting the central nervous system, liver, kidneys, and reproductive system. Short-term exposure at high concentrations can cause dizziness, headaches, confusion, and loss of coordination, essentially because these chemicals depress brain function in a way similar to anesthesia. Chronic, lower-level exposure over months or years is associated with lasting neurological effects, liver disorders, and kidney disease.
The cancer risk is the most closely watched concern. The International Agency for Research on Cancer (IARC) classifies TCE as a Group 1 carcinogen, meaning there is sufficient evidence that it causes cancer in humans. PERC is classified as Group 2A, a probable human carcinogen. The EPA echoes these concerns: its drinking water standards list liver problems and increased cancer risk as the potential health effects of both chemicals.
The EPA has set the maximum contaminant level for TCE, PERC, and carbon tetrachloride in drinking water at 0.005 milligrams per liter (5 parts per billion). The goal for all three is zero. For workers, OSHA regulates airborne exposure separately for each chemical. Methylene chloride, for example, has a permissible exposure limit of 25 parts per million averaged over an eight-hour workday, with a short-term ceiling of 125 parts per million over any 15-minute window.
How They Contaminate Groundwater
Chlorinated solvents behave differently from oil or gasoline when they reach groundwater, and this is what makes them so difficult to clean up. Oil floats on water. Chlorinated solvents are denser than water, so they sink. Environmental scientists call them dense nonaqueous phase liquids, or DNAPLs. When spilled or leaked, a chlorinated solvent seeps downward through soil, passes through the water table, and continues sinking through the aquifer until it hits a layer of rock or clay it can’t penetrate.
Once it reaches that barrier, the solvent pools and spreads laterally, sometimes forming underground reservoirs. Along the way, small amounts get trapped in soil pores as residual contamination. Both the pools and the residual pockets slowly dissolve into the surrounding groundwater, releasing contamination across the full thickness of the aquifer. This process can continue for decades, which is why chlorinated solvent plumes are among the longest-lasting and most expensive contamination problems to remediate.
The Shift Away From PERC in Dry Cleaning
The dry cleaning industry is in the middle of a major transition. In January 2025, the EPA finalized a rule under the Toxic Substances Control Act that phases out PERC in dry cleaning over a 10-year period. Starting June 16, 2025, dry cleaners can no longer use PERC in any newly acquired machine. The full prohibition on using PERC in dry cleaning operations takes effect on December 19, 2034. Manufacturers face their own deadlines: by June 2026, they can no longer produce or import PERC except for certain industrial uses that continue under strict workplace protections.
This follows California and several other states that had already begun restricting or phasing out PERC machines at the state level. The transition affects thousands of small businesses that have relied on PERC for decades.
Alternatives Replacing Chlorinated Solvents
Industries have been moving away from chlorinated solvents since the 1990s, driven by both regulation and cleanup costs. The most common replacements fall into a few categories. Aqueous cleaning, which uses heated deionized water sometimes combined with alkaline detergents, has proven effective for many metal-cleaning applications. One well-documented case involved Robert Bosch Corporation replacing both TCE and CFC-113 with deionized water systems. In several of their production lines, heated water alone, without any added detergent, matched the cleaning performance of the solvents it replaced.
Other alternatives include petroleum distillates, terpene-based solvents (derived from plant oils), and supercritical carbon dioxide cleaning. Each has trade-offs in terms of cleaning power, cost, drying time, and compatibility with specific materials. No single replacement works for every application, which is part of why chlorinated solvents have been slow to disappear from some industries despite well-known risks. For dry cleaners specifically, liquid silicone-based solvents and hydrocarbon-based systems are the most common PERC alternatives currently on the market.