Perchloroethylene, often abbreviated as PCE or Perc, is an industrial chemical known formally as tetrachloroethylene. This substance is a manufactured, colorless liquid belonging to the class of volatile organic compounds (VOCs), meaning it easily evaporates into the air. PCE is a powerful solvent used across numerous industries. Its widespread use and resistance to natural breakdown have led to its detection in air, water, and soil globally. Concerns about its potential impact on human health and the environment drive the ongoing study and regulation of this persistent chemical.
Chemical Identity and Primary Applications
PCE is a chlorinated solvent. Its chemical structure provides high stability and non-flammability, offering a safer alternative to earlier, more flammable solvents. PCE functions as a nonpolar solvent, effectively dissolving organic materials like greases, oils, and waxes. The most widely known application of PCE is in the dry cleaning industry, where its ability to clean fabrics without causing shrinkage or fading made it the preferred agent for decades. Beyond textiles, PCE is extensively used in the metalworking sector as a vapor degreasing agent. Its high boiling point and exceptional solvency allow it to efficiently remove contaminants from metal parts before painting or coating, which is a common practice in the automotive and aerospace industries. PCE also serves as a chemical intermediate in the production of other compounds, such as hydrofluorocarbons used as refrigerants.
Common Routes of Human Exposure
Exposure to PCE occurs through multiple pathways, often linked to its industrial and commercial uses. Occupational exposure is historically the highest, affecting workers in dry cleaning, metal degreasing, and chemical manufacturing plants. These individuals are primarily exposed by breathing in the chemical’s vapors or through direct skin contact with the liquid solvent.
For the general public, a common route is environmental contamination, particularly from contaminated groundwater. PCE often leaches into aquifers from industrial spills and waste disposal sites, contaminating drinking water supplies. Another significant pathway is indoor air contamination via vapor intrusion. This occurs when PCE seeps into the soil and groundwater beneath a building, volatilizes, and its vapors rise through foundation cracks, accumulating inside. Exposure also occurs through consumer products containing PCE, such as spot removers, adhesives, sealants, and certain wood cleaners. Residual PCE left on dry-cleaned clothing can off-gas, leading to short-term inhalation exposure.
Documented Health Effects
Exposure to PCE is known to affect multiple organ systems. Acute, or short-term, exposure to high concentrations of PCE vapors mainly targets the central nervous system (CNS). Effects can range from irritation of the eyes and respiratory tract to neurological symptoms like dizziness, headaches, impaired coordination, and sleepiness. In cases of very high exposure, it can lead to unconsciousness and even death.
Chronic, or long-term, low-level exposure is associated with potentially irreversible health problems. The primary effects are often neurological, resulting in impaired cognitive and motor performance. Beyond the nervous system, chronic PCE exposure has been linked to adverse effects on the liver, kidneys, and immune system. The chemical also poses potential risks to the reproductive system and developing fetus.
Regulatory bodies classify PCE based on its potential to cause cancer. The U.S. Environmental Protection Agency (EPA) classifies PCE as “likely to be carcinogenic to humans” by all routes of exposure. The International Agency for Research on Cancer (IARC) has similarly classified it as “probably carcinogenic to humans” (Group 2A). Studies in occupationally exposed populations have suggested associations between PCE exposure and an increased risk of specific cancers, including bladder cancer, non-Hodgkin lymphoma, and multiple myeloma.
Environmental Behavior and Cleanup Methods
Once PCE is released into the environment, its physical and chemical properties dictate its behavior and persistence. Because it is denser than water, PCE is classified as a dense non-aqueous phase liquid (DNAPL). When spilled, it tends to sink through the soil until it reaches an impermeable layer, creating a persistent contamination source in the subsurface and groundwater. This density and low solubility in water mean that traditional methods of cleaning up groundwater are often ineffective. The chemical’s volatility means it can readily evaporate from contaminated soil and groundwater, leading to the vapor intrusion pathway. Remediation of PCE-contaminated sites is both complex and expensive due to its DNAPL nature.
Common Cleanup Technologies
Common cleanup technologies include:
- Pump-and-treat systems, which extract contaminated groundwater for above-ground treatment.
- Soil vapor extraction (SVE), which uses a vacuum to remove volatile vapors from the soil.
More advanced methods are often employed to address the DNAPL source zones:
- In-situ chemical oxidation, where reactive chemicals are injected into the ground to chemically break down the PCE.
- Thermal treatment, which heats the subsurface to vaporize the contaminant for collection.
- Biological treatments, such as enhanced in-situ bioremediation, which encourage the growth of specific microorganisms that can break down PCE, although this process can sometimes produce more harmful byproducts.