What Is Tetrachloroethylene (PCE)?

Tetrachloroethylene, commonly abbreviated PCE and also called perchloroethylene or tetrachloroethene, is a chlorinated industrial solvent. It is a dense, nonflammable, volatile organic compound that was widely used because it dissolves oils, greases, waxes, and other hydrophobic materials while being relatively stable under many industrial conditions. PCE is best known for its historic and ongoing use in dry cleaning, but it has also been used in vapor degreasing, metal cleaning, textile processing, chemical manufacturing, and specialty solvent applications.

PCE is a high-priority drinking water contaminant because it can persist in subsurface environments for long periods and can migrate through groundwater as a plume. Unlike many contaminants that dilute quickly or bind strongly to soil, PCE can behave as a dense non-aqueous phase liquid, or DNAPL, when released in sufficient quantity. Because it is denser than water, it may sink through an aquifer and collect in low-permeability zones, fractures, or depressions in bedrock, where it can slowly dissolve into groundwater for years or decades.

In drinking water, PCE is usually associated with industrial history rather than with natural geology. Contamination often traces back to dry-cleaning facilities, solvent storage areas, machine shops, electronics manufacturing sites, landfills, leaking drums, improper disposal practices, or contaminated industrial sewers. Small releases can matter because drinking water standards for PCE are typically in the low microgram-per-liter range.

PCE is also relevant beyond ingestion. Because it is volatile, contaminated water can release PCE into indoor air during showering, bathing, laundry, dishwashing, and other household uses. In areas with shallow contaminated groundwater, PCE and related chlorinated solvents may also enter buildings as vapor intrusion through cracks, utility penetrations, sump openings, or foundation gaps.

Scientific Identity

Tetrachloroethylene has the chemical formula C2Cl4 and CAS number 127-18-4. Its systematic chemical name is tetrachloroethene, reflecting an ethene structure in which all four hydrogen atoms have been replaced by chlorine atoms. This high chlorine content gives PCE many of the properties that make it useful industrially and problematic environmentally: chemical stability, high density, low flammability, moderate water solubility, and strong volatility compared with many nonchlorinated organic chemicals.

PCE is classified as a chlorinated volatile organic compound, or chlorinated VOC. It is not a metal, radionuclide, nutrient, or microbial contaminant. It is a synthetic organic chemical that is measured in drinking water at very low concentrations, typically reported as micrograms per liter. PCE has a recognizable solvent odor at higher concentrations, but odor is not a reliable safety indicator because harmful or regulated levels may be far below the level most people can smell.

In the subsurface, PCE may undergo reductive dechlorination under anaerobic conditions. This transformation can produce trichloroethylene (TCE), dichloroethylene isomers, vinyl chloride, and eventually ethene if degradation is complete. This is important because some degradation products, especially vinyl chloride, are themselves major drinking water contaminants and carcinogenic concerns. Detection of PCE in a well may therefore indicate a broader chlorinated solvent problem rather than a single isolated chemical.

How Tetrachloroethylene (PCE) Enters Drinking Water

PCE enters drinking water primarily through releases to soil and groundwater. Historical dry-cleaning operations are among the most common sources. Releases may have occurred from leaking solvent tanks, floor drains, wastewater discharges, improperly discarded filter residues, spills during machine maintenance, or disposal of separator water containing solvent. Older dry-cleaning sites can remain a source even after the business has closed or changed ownership.

Industrial facilities that used PCE for degreasing or cleaning metal parts can also contaminate aquifers. Vapor degreasing units, solvent sumps, transfer lines, drum storage areas, and waste handling zones may release PCE to concrete, soil, stormwater systems, or sanitary sewers. Once in the subsurface, PCE can partition between pure liquid solvent, dissolved groundwater contamination, sorbed mass on soil organic matter, and soil gas.

Landfills, hazardous waste sites, military installations, manufacturing plants, and industrial parks are additional source categories. PCE has also been detected near former solvent recyclers and waste disposal facilities where mixed chlorinated solvents were handled. Because PCE can form long, narrow plumes, a drinking water well may be affected even if the original release site is some distance away.

Private wells are particularly vulnerable where they draw from shallow or fractured aquifers near industrial or commercial corridors. Public water systems may also be affected if municipal wells intercept a plume. Water utilities generally monitor regulated VOCs, but small private well owners are usually responsible for arranging their own testing.

Occurrence and Exposure

PCE is most often found in groundwater rather than surface water because many major releases begin below ground or migrate downward through soil. Surface water contamination can occur near industrial discharge points, contaminated stormwater pathways, or groundwater discharge zones, but PCE’s volatility and dilution often reduce persistence in open surface waters compared with aquifers.

Exposure from drinking water includes ingestion, inhalation, and dermal contact. Ingestion occurs when contaminated water is used for drinking, coffee, tea, ice, cooking, or infant formula preparation. Inhalation can occur when PCE volatilizes from hot or agitated water during showers, baths, dishwashing, and laundry. Dermal absorption may occur during bathing, although inhalation and ingestion are often the more important exposure routes for volatile solvents.

Occurrence is highly site-specific. One neighborhood may have no detectable PCE, while another nearby area may be affected by a narrow plume from a former dry cleaner or industrial facility. Concentrations can vary by well depth, pumping rate, seasonal groundwater flow, and proximity to source areas. In fractured bedrock aquifers, contamination may be irregular, with one well affected and another nearby well testing clean.

PCE contamination can also be accompanied by TCE, cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, 1,1-dichloroethylene, vinyl chloride, carbon tetrachloride, chloroform, or petroleum-related solvents depending on the release history. A full VOC scan is often more informative than testing for PCE alone.

Health Effects and Risk

PCE is treated as a high-risk drinking water contaminant because of its toxicity profile, persistence, and association with cancer risk. Health agencies have classified PCE as a cancer concern based on evidence from occupational studies, animal studies, and mechanistic toxicology. The strongest concerns include possible associations with bladder cancer, non-Hodgkin lymphoma, multiple myeloma, and other cancer endpoints, although classifications and wording vary by agency.

Noncancer effects are also important. PCE can affect the central nervous system, especially at higher exposure levels, causing symptoms such as dizziness, headache, fatigue, impaired coordination, or irritation in occupational or accidental exposure settings. Drinking water exposures are usually much lower than workplace solvent exposures, but chronic exposure over many years is the regulatory concern.

The liver and kidneys are key target organs because they participate in metabolism and elimination of chlorinated solvents. Toxicological studies have identified liver and kidney effects as important endpoints for risk assessment. There is also concern about developmental, reproductive, immune, and neurological effects, particularly where exposure includes both drinking water ingestion and inhalation from indoor water use.

Risk depends on concentration, duration, exposure route, age, health status, and co-occurring contaminants. Infants, pregnant people, people with liver or kidney disease, and residents using contaminated private wells for all household purposes may warrant extra caution. Because PCE is volatile, reducing only the drinking water ingestion route may not fully control exposure if contaminated water is still used for showering and other indoor activities.

Testing and Monitoring

PCE requires laboratory testing designed for volatile organic compounds. Common analytical approaches include purge-and-trap gas chromatography/mass spectrometry, such as methods used by certified laboratories for regulated drinking water VOCs. In the United States, public water systems and environmental investigations may use EPA-approved drinking water VOC methods or related laboratory methods such as those used for groundwater and hazardous waste site assessment.

Proper sampling is critical because PCE can volatilize if samples are mishandled. Water is usually collected in small glass VOC vials with no headspace, meaning no air bubble should remain in the container. The sample may be preserved according to laboratory instructions and kept cold during transport. Samples should be analyzed within the required holding time. A sample collected in an ordinary bottle, partially filled container, or container with trapped air may underestimate the true concentration.

For private wells, a targeted VOC panel is preferable to a single-analyte test because PCE often occurs with other chlorinated solvents or degradation products. Testing may be especially important near dry cleaners, machine shops, industrial parks, landfills, Superfund or brownfield sites, military facilities, solvent storage areas, or neighborhoods with known vapor intrusion investigations.

Field screening tools such as photoionization detectors can help identify solvent vapors during site investigations, but they do not replace laboratory water analysis. Odor, taste, and appearance are not reliable indicators. PCE can exceed health-based or regulatory levels in water that looks completely clear and has no obvious smell.

Treatment Methods

Activated carbon and air stripping are the most established drinking water treatment approaches for PCE. The best option depends on concentration, flow rate, household exposure concerns, co-contaminants, and whether treatment is needed at one tap or for the entire building. Because PCE can be inhaled after volatilizing from water, whole-house treatment may be more protective than a single kitchen filter when concentrations are significant.

Activated carbon deserves particular attention for PCE because it is widely available and highly effective when correctly applied. PCE adsorbs strongly to high-quality activated carbon, especially granular activated carbon systems designed for VOCs. For private wells, a point-of-entry system is often preferred when PCE is above a health-based or regulatory level because it reduces ingestion and inhalation pathways throughout the home.

Activated carbon can fail if it is undersized, exhausted, installed at too high a flow rate, or not monitored. Natural organic matter, fuel-related compounds, other solvents, and poor pretreatment can consume adsorption capacity. Iron, manganese, sediment, or biofouling can interfere with flow and contact time. For contaminated wells, a lead-lag arrangement with sampling ports between two carbon vessels is a stronger design than a single tank because it allows breakthrough detection before the second tank is exhausted.

Regulations and Guidelines

PCE is regulated or guideline-listed in many drinking water programs because it is a toxic chlorinated solvent and a common groundwater contaminant. In the United States, the U.S. Environmental Protection Agency has established a federal Maximum Contaminant Level for tetrachloroethylene in public drinking water systems. The U.S. federal enforceable limit is commonly cited as 5 micrograms per liter, or 0.005 milligrams per liter, for public water supplies. States may implement the federal requirement and may also have additional monitoring, cleanup, notification, or groundwater standards.

International values vary. The World Health Organization has published a drinking-water guideline value for tetrachloroethene, and several countries maintain their own national limits or health-based values. The European Union regulates tetrachloroethene and trichloroethene together as a combined parameter in drinking water. Canada and other jurisdictions have their own maximum acceptable concentrations or guideline values. Because values can differ by country, province, state, or local regulatory program, the applicable limit should be checked against the authority responsible for the specific water supply.

Regulatory compliance for public water systems does not always answer private well safety questions. Private wells are often not covered by routine public water monitoring requirements, and owners may need to test voluntarily. In contamination investigations, cleanup goals for groundwater, indoor air, and vapor intrusion may differ from drinking water standards. A PCE result should therefore be interpreted in context: drinking water use, household exposure routes, local standards, plume history, and co-contaminants all matter.

Related Contaminants

Frequently Asked Questions

Is PCE the same chemical used in dry cleaning?

Yes. PCE, also called perchloroethylene, has been one of the most widely used dry-cleaning solvents. Many groundwater plumes are associated with current or former dry-cleaning facilities where solvent was spilled, leaked, discharged to drains, or improperly disposed of.

Can I smell PCE in contaminated drinking water?

Not reliably. PCE has a solvent-like odor at sufficiently high concentrations, but regulated and health-relevant concentrations may be far below the odor threshold. Clear, odorless water can still contain PCE above a drinking water limit or health advisory level.

Is a refrigerator or pitcher filter enough for PCE?

Usually not unless the filter is specifically certified for VOC reduction and replaced on schedule. Even then, a small point-of-use filter only treats water at that dispenser. If PCE is present at concerning levels, point-of-entry activated carbon may be needed to reduce inhalation exposure from showers and other household uses.

Does boiling water remove PCE?

Boiling is not recommended. Because PCE is volatile, heating water can transfer the chemical into indoor air, potentially increasing inhalation exposure. Use a validated treatment system such as activated carbon or an engineered air-stripping system instead.

What should a private well owner do if PCE is detected?

Confirm the result with a certified laboratory VOC test, test for related chlorinated solvents such as TCE and vinyl chloride, avoid relying on boiling, and consult the local health department or environmental agency. If concentrations are above applicable standards or health-based guidance, install appropriately designed treatment and monitor for breakthrough.