Perchloroethylene (PCE), also known as “perc,” is a synthetic chemical widely used in industrial and commercial settings for decades. Its effectiveness as a solvent made it popular, particularly in the dry cleaning industry, where it removes stains and grease from fabrics. PCE is also a recognized environmental contaminant, frequently detected in soil, groundwater, and indoor air, raising public health concerns.
Chemical Identity and Characteristics
PCE is chemically known as Tetrachloroethylene, a chlorinated hydrocarbon with the formula \(\text{C}_2\text{Cl}_4\) and CAS Registry Number 127-18-4. It is classified as a volatile organic compound (VOC), meaning it easily evaporates into the air at room temperature. This volatility contributes to its presence in both outdoor and indoor air environments.
PCE is a clear, colorless liquid that is denser than water, a property that influences its environmental behavior. While non-flammable under normal conditions, it decomposes at very high temperatures (over \(600^\circ\text{F}\) or \(316^\circ\text{C}\)) to form hazardous products like phosgene and hydrogen chloride. The solvent has a mildly sweet, ether-like odor, but the ability to detect this smell fades quickly, making odor an unreliable warning sign of high concentration exposure.
Principal Applications and Sources of Exposure
PCE’s primary utility is its power to dissolve organic materials like fats, greases, and oils, making it an effective cleaning agent. Its stability and non-flammable nature led to its adoption as a leading solvent in dry cleaning operations worldwide, where it is often called “perc.” Although its use has declined due to regulations, dry cleaning remains a major source of public exposure. PCE is also used in metal degreasing, specifically vapor degreasing, to clean manufactured parts in the automotive and metalworking industries. It serves as a chemical intermediate in the production of other chemicals, and is found in consumer products like adhesives, spot removers, and wood cleaners.
Exposure typically occurs through inhalation, which is the most significant route for both occupational and general populations. People may inhale residual PCE vapors released from newly dry-cleaned clothes or from the air inside buildings near industrial facilities or former dry cleaners. Ingestion is also a concern, as PCE can contaminate drinking water from groundwater sources near spill sites.
Health Effects and Safety Precautions
Exposure to PCE can lead to both acute (short-term) and chronic (long-term) health concerns, depending on the concentration and duration of exposure. Acute inhalation of high levels, such as in poorly ventilated industrial settings, can irritate the eyes and upper respiratory tract. PCE acts as a central nervous system (CNS) depressant, causing symptoms like dizziness, headache, confusion, and impaired coordination.
Chronic exposure to lower levels has been associated with severe, long-term health outcomes, primarily affecting the nervous system, liver, and kidneys. Studies of workers exposed over many years suggest potential neurobehavioral impairment, including cognitive and motor function deficits. The International Agency for Research on Cancer (IARC) has classified PCE as probably carcinogenic to humans (Group 2A), based on evidence from human and animal studies.
To reduce personal exposure, especially concerning dry-cleaned items, it is advisable to unwrap and air out clothing in a well-ventilated area, such as outdoors or in a garage. In occupational settings, proper engineering controls, like fully enclosed dry cleaning machines and robust ventilation systems, are necessary to prevent vapor buildup. Regulatory bodies have also established maximum contaminant levels in drinking water to limit ingestion exposure.
Environmental Behavior and Cleanup
PCE is a persistent, man-made chemical highly resistant to natural breakdown processes. Because its density is greater than water, it is classified as a Dense Non-Aqueous Phase Liquid (DNAPL). When spilled, PCE sinks through the soil and continues downward through the aquifer until it reaches an impermeable layer, causing long-term groundwater contamination.
Its tendency to sink and low solubility mean a pool of PCE can remain in the subsurface as a continuous source of contamination for decades. Once in the groundwater, it can volatilize, with vapors migrating upward through the soil and into nearby buildings. This process, known as vapor intrusion, degrades indoor air quality, leading environmental agencies to regulate the chemical to protect public water supplies.
The cleanup of PCE contamination is challenging because its DNAPL properties render traditional “pump-and-treat” methods less effective. Remediation efforts focus on “source reduction” using advanced technologies to remove or destroy the chemical in the aquifer. These methods include soil vapor extraction, in situ chemical oxidation to break down the solvent, and bioremediation, which uses specialized microorganisms to degrade the PCE.