Volatile organic compounds (VOCs) are a broad range of organic chemicals containing carbon and hydrogen. They are categorized by their volatility and their ability to evaporate under standard conditions (defined as normal room temperature and pressure).
They have a high vapor pressure and a low boiling point at room temperature. This causes large numbers of molecules to evaporate where they can cause harm to the environment and human health.
The vast majority of VOCs are manmade, but some are naturally occurring. These include isoprene (which is produced by plants), in addition to other VOCs from animals and microbes. Manmade sources include:
- Paints, coatings and solvents
- Methyl chloride used in adhesive removers and aerosol spray paint
- Formaldehyde which is found in paints, wall boards, adhesives and ceiling materials
- CFCs and chlorocarbons such as tetrachloroethene used in dry cleaning and industry
- Perchloroethylene, which is also used in dry cleaning
- Fossil fuels – either directly, as a product such as gasoline, or a by-product like exhaust gas
- Benzene, which is found in tobacco smoke, stored fuel, and car exhausts
Dangerous to the Environment
Emitting VOCs into the atmosphere can be incredibly harmful to the environment. Large quantities can disrupt natural processes in plants and cause the formation of low-level ozone. While ozone is beneficial higher up in the atmosphere, where it prevents ultraviolet light from the sun reaching Earth, at lower levels, it can be dangerous as it causes smog. Smog has a debilitating effect on the whole environment, destroying crops and forests, as well as causing respiratory and heart problems in humans.
Hazardous to Health
VOCs are dangerous to human health if inhaled in large quantities over a long period of time. Their vapors are flammable at low concentrations and toxic even at low levels.
Many VOCs cause respiratory, allergic, or immune effects, especially in the young. Eye, nose and throat irritation, headaches, loss of coordination, and nausea are not uncommon. The chemicals are also linked to liver, kidney, and central nervous system damage, as well as cancer in animals. Many are also suspected or known to cause cancer in humans, and congenital disabilities have been observed following catastrophic accidental release into the atmosphere.
Some of the population are more likely to be exposed to VOCs than others: workers in the oil and gas, petrochemical, chemical, and paint industry, for example, will be exposed to greater levels than those not working in this sector. People in the building trade are also likely to be at a greater risk as many building products, such as paints, solvents, and glues give off VOCs. For this reason, many workers wear electronic devices to monitor their exposure to a substance over a working day, taking into account average levels of the substance and the time spent in the area. This is known as ‘time-weighted average’, and ensures they are not overexposed to toxicity over a given time span.
However, VOCs could be used as a biomarker for detecting cancer. Different patterns of VOCs found in exhaled breath, blood, urine, feces, or sweat correlate with various diseases. This correlation is based on the hypothesis that pathological processes occurring as a result of disease can either generate VOCs which are not normally produced by the body or alter the concentration of those that are. These constitute biomarkers for the assessment or detection of diseases. Cancer cells in vitro have been shown to produce or consume specific VOCs that could act as potential biomarkers to differentiate them from non-cancerous cells.
Industrial sources of VOCs require monitoring by law. This is usually done using Flame Ionisation Detection or Photo Ionisation Detection, both of which rely on the principle of burning organic vapors in order to produce positively charged carbon ions as an intermediate product of combustion. The ions can be collected on an electrode, and an electrical current equivalent to the amount of carbon ions present is produced. From this, the actual VOC concentration can be inferred, assuming the proportions of VOCs being measured is known.
It is incredibly important to monitor the levels of VOCs emitted into the environment. Not only can they be harmful to the environment, slowly destroying plants, disrupting their normal functioning, and chocking crops to death. They can also affect human health, with impacts ranging from respiratory distress to cancer and disease.
References and Further Reading