What Is Trichloroethylene (TCE)?

Trichloroethylene, commonly called TCE, is a synthetic chlorinated solvent historically used for metal degreasing, vapor degreasing, parts cleaning, chemical manufacturing, and some extraction processes. It is a volatile organic compound, meaning it can evaporate from water into air, but it is also persistent enough in groundwater to create long contaminant plumes that may remain a drinking water concern for decades after the original release.

TCE became widely used because it dissolves oils, greases, waxes, and many industrial residues very effectively. That same solvent behavior makes it environmentally important: when spilled or disposed of improperly, TCE can move through soil, sink below the water table, and contaminate aquifers used for private wells and public water supplies. It is denser than water in its pure liquid form, so concentrated releases can migrate downward as dense non-aqueous phase liquid, creating difficult-to-remediate source zones.

In drinking water safety, TCE is treated as a high-concern industrial chemical because it has been associated with cancer and noncancer toxicity at low exposure levels. It is also a vapor intrusion concern. Contaminated groundwater can release TCE vapor into soil gas, and those vapors can enter basements, crawl spaces, utility corridors, and buildings above or near a plume. For households with TCE-contaminated water, exposure may occur not only by drinking but also through showering, bathing, dishwashing, and other indoor water uses that allow the chemical to volatilize.

Scientific Identity

TCE is an unsaturated chlorinated hydrocarbon with the chemical formula C2HCl3 and CAS number 79-01-6. It is also known chemically as trichloroethene. Its molecular structure contains a carbon-carbon double bond with three chlorine atoms and one hydrogen atom, giving it high solvent power and significant volatility compared with many less chlorinated organic chemicals.

In environmental chemistry, TCE is classified as a chlorinated volatile organic compound, or chlorinated VOC. It has moderate water solubility, low taste and odor warning reliability at health-relevant concentrations, and a tendency to partition between water, soil gas, and organic matter. Because it volatilizes, water samples must be collected in special sealed vials without headspace; otherwise, TCE can escape before laboratory analysis and produce falsely low results.

TCE can also participate in subsurface degradation processes. Under anaerobic conditions, some microorganisms can reductively dechlorinate TCE to dichloroethylene isomers, vinyl chloride, and ultimately ethene if degradation proceeds completely. Partial degradation is a major concern because vinyl chloride is highly toxic and carcinogenic. Therefore, a TCE plume is often evaluated together with its daughter products, especially cis-1,2-dichloroethylene and vinyl chloride.

How Trichloroethylene (TCE) Enters Drinking Water

The most important route into drinking water is industrial release to soil and groundwater. Historic metalworking, aerospace, electronics, automotive, weapons manufacturing, machine shops, and maintenance facilities used TCE extensively as a degreasing solvent. Leaking storage tanks, disposal pits, floor drains, sumps, degreaser spills, contaminated stormwater systems, and poor waste handling practices allowed TCE to enter the subsurface at many sites before modern hazardous waste controls were in place.

Once in the subsurface, TCE can migrate as dissolved contamination in groundwater. Because many aquifers move slowly, plumes can extend from an original source area to downgradient neighborhoods, farms, public well fields, or private wells. Pumping wells can also alter groundwater flow, drawing contamination toward a water supply well that was not originally in the center of the plume.

TCE may also enter water supplies from hazardous waste sites, landfills, industrial lagoons, military bases, former manufacturing properties, and solvent-contaminated sediments. In some settings, TCE is found with tetrachloroethylene, carbon tetrachloride, benzene, toluene, xylene, fuel compounds, or chlorinated degradation products. Public systems using surface water are generally less vulnerable than groundwater systems because TCE tends to volatilize, but contaminated industrial discharges or groundwater inputs can still affect rivers and reservoirs in specific cases.

Occurrence and Exposure

TCE occurrence is strongly site-specific. It is not a naturally occurring drinking water constituent; its presence usually indicates industrial contamination, historical solvent use, a contaminated aquifer, or migration from a waste disposal area. It is frequently investigated at Superfund sites, military installations, aerospace and defense manufacturing sites, industrial parks, former degreasing facilities, and areas with long histories of chlorinated solvent use.

Private well users can be at particular risk because private wells are often not routinely tested for VOCs unless the owner requests testing or a local agency identifies a contamination plume. A well may appear clear, have no unusual taste, and still contain TCE above health-based screening levels. Shallow wells near industrial corridors, older manufacturing districts, rail yards, landfills, and known hazardous waste sites deserve special attention.

Exposure can occur through ingestion of contaminated drinking water, inhalation of vapors released during showering or other household water use, and dermal contact during bathing. In buildings above contaminated groundwater, vapor intrusion can add a separate inhalation exposure even if drinking water is not being consumed. For this reason, investigations of TCE often consider both water testing and indoor air or soil gas assessment.

Health Effects and Risk

TCE is considered a high-risk drinking water contaminant because it has been linked to both cancer and noncancer health effects. The International Agency for Research on Cancer classifies trichloroethylene as carcinogenic to humans, and the U.S. Environmental Protection Agency has characterized it as carcinogenic to humans by all routes of exposure. Kidney cancer is a central concern, and evidence has also been evaluated for liver cancer and non-Hodgkin lymphoma.

Noncancer effects can involve the immune system, liver, kidneys, nervous system, and developing fetus. High-level occupational or accidental exposures can cause dizziness, headache, central nervous system depression, and effects on coordination. Drinking water concerns focus on chronic, lower-level exposure over months or years, where the primary issues include increased lifetime cancer risk, immune toxicity, kidney toxicity, liver effects, and developmental toxicity.

Some health agencies have paid special attention to TCE exposure during pregnancy because studies and toxicological evaluations have raised concerns about developmental effects, including possible cardiac developmental impacts. Risk depends on concentration, exposure duration, route of exposure, age, pregnancy status, underlying health, and whether other chlorinated solvents or petroleum chemicals are also present. Because TCE can volatilize during household water use, inhalation may contribute meaningfully to total exposure in addition to drinking the water.

Testing and Monitoring

TCE cannot be reliably identified by sight, taste, or odor at concentrations relevant to health protection. Testing requires specialized laboratory analysis for volatile organic compounds. Common methods include purge-and-trap gas chromatography/mass spectrometry, such as U.S. EPA Method 524.2 or related VOC methods for drinking water. Laboratories typically report TCE in micrograms per liter, also expressed as parts per billion in water.

Proper sample collection is essential. VOC samples are usually collected in small glass vials with preservatives as required by the laboratory, filled so there is no air bubble or headspace, capped tightly, chilled, and delivered within the specified holding time. If the sample is aerated, shaken, or left partially filled, TCE can escape into the air and the result may underestimate the true concentration.

For private wells near a known plume, a single test may not be enough. Concentrations can vary seasonally or with pumping patterns, groundwater levels, and nearby remediation systems. Public water systems typically monitor regulated VOCs according to national or state requirements, but monitoring frequency depends on the system type, source water vulnerability, prior results, and local regulatory decisions. Where vapor intrusion is suspected, water testing may be paired with indoor air, sub-slab soil gas, or crawl-space sampling.

Treatment Methods

TCE is treatable, but treatment must be selected and maintained carefully. Because it is volatile and adsorbs to carbon, the two most established technologies are activated carbon and air stripping. The best residential approach depends on whether exposure is limited to drinking and cooking water or whether whole-house inhalation and bathing exposures are also important.

Activated carbon works best when it is properly engineered rather than treated as a generic filter. TCE competes for adsorption sites with other VOCs and natural organic matter. Carbon can fail early if the contaminant concentration is high, if flow is too fast, if the cartridge is undersized, or if replacement is based only on taste or calendar estimates without water testing. Because TCE has little odor warning at unsafe concentrations, breakthrough monitoring is important.

Point-of-use activated carbon may be reasonable when TCE is detected at low levels and the main goal is reducing ingestion from a single drinking water tap. Point-of-entry treatment is generally more protective when concentrations are elevated, when children or pregnant people are present, or when inhalation during showering may be significant. For public systems and larger contaminated wells, air stripping and granular activated carbon are often combined, with routine compliance monitoring after treatment.

Regulations and Guidelines

TCE is regulated or specifically evaluated in many drinking water programs because of its toxicity, mobility in groundwater, and history of widespread industrial use. In the United States, the EPA has established a federal Maximum Contaminant Level for trichloroethylene in public drinking water of 0.005 mg/L, equivalent to 5 micrograms per liter. The EPA’s health-based goal for carcinogens may be lower than the enforceable limit, and public systems must comply with applicable monitoring and treatment requirements.

International and national guideline values vary. The World Health Organization has published a health-based guideline value for trichloroethene in drinking water, and many countries use their own risk assumptions, analytical capabilities, and regulatory frameworks when setting limits. The European Union and some national programs regulate chlorinated solvents individually or in combined parameters, such as sums of trichloroethene and tetrachloroethene. Local standards may also be stricter in areas with known groundwater plumes or vapor intrusion concerns.

For private wells, legal requirements are often limited or absent, even where nearby public water systems are regulated. Well owners should consult local health departments, environmental agencies, or certified laboratories for the appropriate VOC test panel and for interpretation against current state, provincial, national, or regional health-based levels. If TCE is detected, results should be evaluated with related compounds such as PCE, dichloroethylene, and vinyl chloride, because these can affect both health risk and treatment design.

Related Contaminants

Frequently Asked Questions

Is TCE in drinking water usually from natural sources?

No. TCE is a synthetic industrial solvent. Detection in drinking water usually points to industrial releases, historic degreasing operations, spills, contaminated waste sites, leaking tanks, or migration from a chlorinated solvent groundwater plume.

Can I smell or taste TCE in my tap water?

Not reliably. TCE may have a solvent-like odor at higher concentrations, but health-relevant levels can occur without noticeable taste, odor, or discoloration. Laboratory VOC testing is the only dependable way to confirm its presence.

Is a refrigerator filter enough to remove TCE?

Usually not unless the filter is specifically certified or documented for VOC reduction and has adequate carbon capacity. Many refrigerator filters are designed mainly for chlorine taste and odor, not for chlorinated solvent contamination. A properly selected activated carbon system is more appropriate.

Should TCE treatment be installed at one tap or for the whole house?

It depends on the concentration and exposure scenario. A point-of-use activated carbon unit can reduce ingestion from one drinking water tap. Point-of-entry treatment is more appropriate when showering, bathing, laundry, or whole-house vapor release could contribute substantially to exposure.

Does boiling water remove TCE?

Boiling is not recommended. Because TCE is volatile, boiling can transfer it from water into indoor air and increase inhalation exposure. Use an appropriate activated carbon or engineered treatment system instead, and confirm performance with follow-up testing.