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Synonyms: perchloroethene, tetrachloroethene, tetrachloroethylene, may also be referred to as “Perc”
Overview: PCE is an organic chemical introduced in environment by human activity. Specifically, it is a widely used solvent, especially in dry cleaning activities. PCE is also used as a degreaser and in some consumer products (e.g., shoe polish, typewriter correction fluid). Although not theoretically impossible, there is no evidence that PCE forms or occurs naturally in the environment. Thus, its detection in an environmental sample (e.g., groundwater, surface water, soil, indoor, or ambient air) is associated with PCE spills or accidental release.
PCE is toxic to humans at very low concentrations. The Environmental Protection Agency has established a Maximum Contaminant Level for PCE in water of 5 parts per billion (or micrograms per Liter). At this low amount, practically PCE cannot be perceived by smell or taste. For example, people may smell PCE in air at concentrations above 1 ppm (parts per million).
Where Is PCE Used/Found?
- dry cleaning / dry cleaned clothes
- degreasing activities / industrial sites
- consumer products (e.g., shoe polish, typewriter correction fluid)
- manufacturing and auto repair shops
- manufacturing of chlorofluorocarbons
- auto paint
General Description/ Properties
PCE is a halogenated organic compound composed of 2 atoms of carbon and 4 atoms of chlorine (two chlorine atoms linked to each carbon). The two carbons are linked with each other by a double chemical bond. Thus, PCE does not contain any hydrogen atoms.
PCE is a colorless liquid with a sweetish smell which is not flammable under normal temperature and pressure. It is part of a class of chemicals also known as halogenated volatile organic compounds (HVOCs). This means that PCE evaporates (goes from liquid into gaseous form when in contact with air).
PCE is also part of a class of chemicals referred to as “chlorinated solvents”. Due to the presence of one or more chlorine atoms in their structure chlorinated solvents are heavier than water. Chlorinated solvents are also referred to as Dense Non-Aqueous Phase Liquids (DNAPLs).
Environment Fate and Transport
Basically, when spilled into the environment, part of the spilled PCE will evaporate, while another part will infiltrate through the ground into the subsurface.
- Air: Once in air, PCE was shown to be oxidized with a half life of 96 days.
- Subsurface: Once in subsurface, PCE will move downward under the influence of gravity. Its downward movement will subsurface be slowed down or sometimes even stopped by layers of low permeability (such as clays or silts). When this happens, PCE will start moving laterally following the slope of the low permeability layer until it either reaches a dip in the layer and accumulates in pools or until it finds a hole in the layer which enables further downward movement. Usually groundwater will also sit on less permeable subsurface layers thus the subsurface accumulated pools of PCE will serve as a secondary source providing PCE into water continuously until the PCE underground accumulated pool gets depleted.
- Groundwater: When it comes in contact with groundwater, PCE will start dissolving in groundwater until it reaches its solubility limit. Thus, when in contact with groundwater part of PCE will solubilize and the remaining part will continue to travel downward percolating the water table and accumulating at the bottom of the water since PCE is heavier (more dense) than water. The PCE sitting on the bottom of water will act as a secondary source by continuously dissolving PCE into the water.
Thus, PCE may travel in the subsurface as a DNAPL, as a dissolved phase into groundwater, and as a gaseous phase. As a DNAPL PCE may accumulate on the bottom of groundwater table in a dip. DNAPL flow direction is in general independent from groundwater flow direction, as it relates to sloping of underground low permeable layers. In contrast, the dissolved PCE phase will travel with groundwater. During subsurface transport, some PCE may be absorbed to soil particles. However, PCE does not strongly sorb to soil.
What makes PCE a problematic pollutant is its resistence to degradation/biodegradation. Unlike, petroleum hydrocarbons (which usually degrade fast in the environment) PCE as other chlorinated solvents.
How Can You Be Exposed to PCE?
- breathing in air contaminated with gaseous PCE:
- indoor air from a building sitting on contaminated soil and/or groundwater
- indoor air from a workplace where PCE is manufactures or used (e.g., in dry cleaning)
- breathing the PCE vapors during a bath or shower with contaminated water (especially when well water and not municipal water is used)
- wearing dry cleaned clothes soon after they are dry cleaned
- breathing in the vicinity of a person which was recently exposed to PCE (e.g., workers) - such person may exhale PCE vapors
Through skin absorption (please note that PCE is not efficiently absorbed through the skin):
- Playing on contaminated ground
- Bathing in contaminated water
- Spending time in a contaminated atmosphere
- wearing dry cleaned clothes soon after they are dry cleaned
- Contaminated water
- Contaminated food
- Accidentally ingest contaminated particles (e.g., soil)
Through breast feeding – since PCE accumulates in milk due to its lipophilic nature
Exposure to PCE may cause a variety of health effects depending on the amount of PCE and exposure time. Such effects may include:
In chronic exposures:
- Skin irritation
- Liver and kidney damage
- Menstrual problems and spontaneous abortions (in exposed women)
In acute exposures (to high amounts of PCE):
- Central nervous system effects (for exposure to more than 100 ppm pf PCE):
- Difficulty in walking and speaking
- Death from respiratory depression (ingestion of more than 1,500 ppm of PCE)
- Death (within 4 hours) – by ingestion of 2,600-4,000 ppm PCE (experiments with rats)
Please note that the data related to such exposure pollution is usually obtain through animal studies and may not be verified in humans, however the potential to cause similar problems in humans remains.
PCE is reasonably anticipated carcinogen, which means that it was proven to cause tumors in mice and it has the potential to cause cancer in humans, especially when exposure to high amounts of PCE have occurred. The following type of cancers may be associated to exposure to PCE:
- Lung cancer
- Cancer of colon-rectum
- Esophageal cancer
- Bladder cancer