Trichloroethane (TCA) Pollution
Synonyms: methyl chloroform, methyltrichloromethane, trichloromethylmethane, alpha trichloroethane
1,1,1-TCA is an organic chemical introduced in the environment by human activity. Although, in theory, its natural formation cannot be excluded, so far it was not reported. Thus, 1,1,1-TCA presence in the environment (water, air, soil) is associated with spills and leaks from facilities using this chemical or from consumer products containing it.
Until recently, 1,1,1-TCA was a widely used solvent in degreasing operations, as well as a solvent in household products such as cleaners, paints, and glues. It is also found in building materials.
1,1,1-TCA is less toxic compared to other chlorinated solvents (such as PCE, TCE, or carbon tetrachloride). However, 1,1,1-TCA was proven to affect the ozone layer, which is why its production has declined and it is no more manufactured for domestic use in the United States. Despite its lower toxicity compared to other chemicals in its class, 1,1,1-TCA can create adverse health effects when exposure to high amounts occurs.
The Environmental Protection Agency has established a Maximum Contaminant Level (MCL) for 1,1,1-TCA in water of 0.2 parts per million (or milligrams per Liter), which is equivalent to 200 parts per billion (ppb or micrograms per Liter). This is higher than the 5 ppb which is the MCL for PCE and also for TCE in water. The limit in air (above which health risk is assumed) is at 350 ppm.
Where Is 1,1,1-TCA Used/Found?
- degreasing activities / industrial sites
- building materials
- household cleaning products
- in aerosol sprays
1,1,1-TCA is a halogenated organic compound composed of 2 atoms of carbon and 3 atoms of chlorine (all chlorine atoms are bound to one carbon atom, while hydrogen is bound to the other carbon atom). The two carbons are bound to each other by a single chemical bond (covalent bond).
1,1,1-TCA is a colorless liquid with a sweet sharp odor. It is little flammable under normal temperature and pressure and it is part of a class of chemicals also known as halogenated volatile organic compounds (HVOCs). This means that it evaporates (part of it goes from liquid into gaseous form when in contact with air).
1,1,1-TCA is also a member of the class of chemicals generically referred to as “chlorinated solvents”. Due to the presence of one or more chlorine atoms in their structure chlorinated solvents are heavier than water. They are also not miscible with water. Thus, 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 1,1,1-TCA will evaporate, while another part will infiltrate through the ground into the subsurface. Thus, 1,1,1-TCA spilled in the environment is found in the following media:
- Air: Once in air, 1,1,1-TCA may slowly degrade and will last for about 6 years. 1,1,1-TCA that evaporates at the surface will contaminate the atmosphere (possibly including indoor air), while the 1,1,1-TCA evaporating in the subsurface will partition into the soil pore air which may gradually move upward and end up into the atmosphere and possibly accumulate in indoor air.
- Subsurface: Once in the subsurface, 1,1,1-TCA will move downward under the influence of gravity. Its downward movement will be slowed down or sometimes temporarily stopped by layers of low permeability (such as clays or silts). When this happens, 1,1,1-TCA will start moving laterally following the slope of the low permeability subsurface 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 1,1,1-TCA will serve as a secondary source providing dissolved phase 1,1,1-TCA continuously until the subsurface pool gets depleted.
- Groundwater: When it comes in contact with groundwater, 1,1,1-TCA will start dissolving until it reaches its solubility limit. The water solubility of 1,1,1-TCA is relatively little (as for most organic chemicals), however, it is much higher than the dissolved concentration considered safe for humans (i.e., compared to 200 ppb). The rest of 1,1,1-TCA will percolate the water table and accumulate at the bottom of the water since it is heavier (denser) than water.
The transport of 1,1,1-TCA in the environment is governed by the physical-chemical characteristics of this chemical, which dictates how much of it will partition into air, water, and soil respectively. Also, its characteristics will determine how much of it will sorb to soil particles, thus retarding its subsurface transport. The degradation (bio- and chemical degradation) of 1,1,1-TCA in the environment is also a function of its structure and characteristics. Without getting into details on physical-chemical characteristics of this compound (largely available from textbooks, MSDS sheets, etc), a summary of 1,1,1-TCA fate and transport in the environment is given below:
- it does not strongly sorb to soil, thus its transport in the environment is less retarded;
- it may accumulate in subsurface on dips of low permeability porous media layer generating a pool that can act as a secondary source in the subsurface;
- part of a spilled 1,1,1-TCA will evaporate having the potential to move upward and enter and accumulate inside buildings (in indoor air);
- when in contact with water, a relatively small amount will solubilize in water, while the rest of 1,1,1-TCA will percolate the water table and move downward (being denser than water);
- it degrades both chemically (by hydrolysis in water) and biologically (especially through anaerobic dehalogenation); however, depending on environmental conditions, its complete degradation may take years and even decades since a release occurred.
How Can You Be Exposed to 1,1,1-TCA?
Through inhalation by the breathing of:
- indoor contaminated air (e.g., from home or office) – simply living in your home may pose a risk if the subsurface below your home is contaminated generating chemical vapors that will move upward into the house (as described above);
- chemical vapors during a bath or shower with contaminated water – for example, if a well is used to provide home water supply, if the groundwater is contaminated with 1,1,1-TCA, then you may be exposed to this chemical not only by drinking the water, but also through breathing the air with evaporated chemical.
Through skin absorption while:
- playing on contaminated ground – for example, kids playing in the ground, or adults playing football or carrying out activities involving disturbing the ground;
- bathing in contaminated water – surface water bodies may also be contaminated, thus swimming in a contaminated water body may expose you to toxic vapors
- living in a space with contaminated air – the chemical vapors from the air either at home or at your workplace may intoxicate you
Through ingestion by consuming:
- contaminated water – for example when well water used to supply the potable water gets contaminated;
- contaminated food – for example vegetables may become contaminated by extracting the chemical dissolved in water from the ground; the source of the extracted chemical could be contaminated soil, or groundwater (in the vegetable growth area) or contaminated irrigation water;
- contaminated particles (e.g., soil, particulate matter dispersed in air) – involving any activity that involves disturbing such particles (e.g., outdoor games)
Exposure to high amounts of 1,1,1-TCA for short times may cause a series of health issues which will disappear when the exposure ceases:
- Skin irritation
- Becoming lightheaded
- Loss of coordination
Much higher amounts of 1,1,1-TCA may cause more serious effects:
- Low blood pressure and cessation of heart beat
- Liver and nervous system may be affected
Exposure to low levels of 1,1,1-TCA is more difficult to evaluate due to the lack of long-term observations which cannot be tested in the lab.
Cancer Effects – 1,1,1-TCA is not classified as a human carcinogen