Indoor volatile organic compounds, or VOCs, are carbon-containing organic chemicals present in indoor air. They come from a large number of indoor sources including building materials, furnishings, consumer products, tobacco smoking, human emissions, and indoor chemical reactions. Pollutants from attached buildings such as garages may also enter indoor living spaces. Outdoor air is also a source of indoor VOCs. Volatile organic compounds are emitted as gases from certain solids or liquids. VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects [15]. Concentrations of many VOCs such as benzene, carbon tetrachloride, perchloroethylene are consistently higher indoors than outdoors. EPA's Office of Research and Development found levels of about a dozen common organic pollutants to be 2 to 5 times higher inside homes than outside, regardless of whether the homes were located in rural or highly industrial areas. EPA studies indicated that while people are using products containing organic chemicals, they can expose themselves and others to very high pollutant levels, and elevated concentrations can persist in the air long after the activity is completed [15].
Organic chemicals are widely used as ingredients in household products. Paints, varnishes and wax all contain organic solvents, as do many cleaning, disinfecting, degreasing, cosmetic and hobby products. Fuels are made up of organic chemicals. All of these products can release organic compounds when used, and, to some degree, when they are stored.
The use of VOC can have many adverse health effects, which may include: eye, nose and throat irritation, headaches, loss of coordination and nausea, damage to liver, kidney and central nervous system.
Some organics can cause cancer in animals, some are suspected or known to cause cancer in humans. A number of the VOCs that are present in indoor air have been shown to cause cancer in animals exposed to high concentrations. A few of these VOCs - for example, formaldehyde and benzene - are considered by many authorities to be proven or probable human carcinogens.
Products like paint strippers, adhesive removers and aerosol spray paints contain methylene chloride. This chemical is known to cause cancer in animals. Also, methylene chloride is converted to carbon monoxide in the body and can cause symptoms associated with exposure to carbon monoxide [15].
Benzene
is a known human carcinogen. The main indoor sources of this chemical are: environmental tobacco smoke, stored fuels, paint supplies, automobile emissions in attached garages [15].
An organic compound used widely in dry cleaning industry is perchloroethylene. In laboratory studies, it has been shown to cause cancer in animals. Recent studies indicate that people breathe low levels of this chemical both in homes where dry-cleaned goods are stored and as they wear dry-cleaned clothing. Dry cleaners recapture the perchloroethylene during the dry-cleaning process so they can save money by re-using it, and they remove more of the chemical during the pressing and finishing processes. Some dry cleaners, however, do not remove as much perchloroethylene as possible all of the time [15].
Other organic chemicals that are present in all purpose cleaners, glass and surface cleaners, household cleaners and polishes are ethylbenzene, toluene, styrene, carbon tetrachloride, dioxane, acetaldehyde, acetophenone, methyl ethyl ketone (2-Butanone) [11].
Building occupants, as well as cleaning personnel, are exposed to a wide variety of air borne chemicals when cleaning agents and air fresheners are used in buildings.
There is substantial evidence that individuals whose occupations include regular cleaning activities in buildings have an increased risk of adverse respiratory health effects and asthma. There is limited evidence that increased non-work-related use of household cleaning sprays by home occupants increases the risks of the same health effects [10].
Cleaning product and air freshener constituents can react with oxidants to generate secondary pollutants. A secondary pollutant is a compound that results after a chemical reaction between primary pollutants (usually volatile and semivolatile organic compounds) and a powerful oxidant (e.g. ozone).
Ozone
from outdoor air is a common initiator for indoor gas-phase oxidation processes. Reactions of ozone with constituents containing unsaturated carbon–carbon bonds are much faster, and serve as a larger source of secondary pollutants, than reactions with constituents containing only saturated carbon-carbon bonds. For example, terpenes can react rapidly with ozone in indoor air generating many secondary pollutants, including toxic air contaminants such as formaldehyde. Furthermore, ozone-terpene reactions produce the hydroxyl radical, which reacts rapidly with other organic chemicals, leading to the formation of other potentially toxic air pollutants. Indoor reactive chemistry involving the nitrate radical and cleaning-product constituents is also of concern, since it produces organic nitrates as well as some of the same oxidation products generated by ozone and hydroxyl radicals.
Because of their potential contributions to urban photochemical smog, product manufacturers and air quality regulators have estimated organic compound emissions from the use of cleaning products. Although cleaning agent use causes a small portion of total outdoor organic compound emissions, the health consequences from this usage appear to be out of proportion to the emissions. This reflects the fact that the proportion of emissions inhaled is much higher when those emissions occur in buildings rather than outdoors.
Another source of indoor air pollution that drew the attention of specialists for the past decade is represented by a group of chemicals called brominated flame retardants. These organic compounds are part of polybrominated diphenyl ethers (PBDEs) family and have been used in high volumes to reduce the flammability of polymers and resins commonly found in furniture and electronic components [16]. Many studies have reported on their universal presence in the environment, from the detection in U.S. house dust to the presence in human tissues and informed about their potential toxicity, both in animals and in humans. They have an impact on thyroid, liver and kidney morphology in adult animals and some neurological and musculoskeletal symptoms in humans [17]. While most of them have been voluntarily withdrawn or banned from commercial or household use, one of the mixtures, decabrominated diphenyl ether (DecaBDE) continues to be produced and used in high volumes. Due to the fact that the use of PBDEs has grown so much controversy, many U.S. state legislatures are currently considering banning of phasing out all types of brominated flame retardants [16].
The table below (Figure 3) shows the main indoor contaminants presented in this unit, their sources and their adverse effects.
Pollutant
|
Sources
|
Adverse Effects
|
Asbestos
|
Insulation, construction materials
|
Risk of chest, abdominal cancers and lung diseases
|
Benzene
|
Tobacco smoke, stored fuels, paint supplies, automobile emissions (in garages)
|
Carcinogen
|
Carbon Dioxide
|
Exhaled breath
|
Headaches, fatigue, drowsiness, eye and throat irritations, cognitive impairment, decision-making problems
|
Carbon Monoxide
|
Unvented gas heaters, leaking chimneys and furnaces, wood and gas stoves, fireplaces, cigarette smoke, automobile exhaust
|
Headaches, fatigue, dizziness
|
Formaldehyde
|
Adhesives, fabric treatments, stains, varnishes
|
Irritations to respiratory system, eyes, nose and throat
Carcinogen
|
Indoor particulate matter (PM)
|
Cooking, candles, fireplaces, unvented space heaters, cigarette smoking
|
Heart and lung diseases
|
Lead
|
Pipes, paint
|
Impairment of mental and physical development; blood cells, kidney, central nervous system problems
|
Nitrogen dioxide
|
Combustion processes, tobacco smoke, kerosene heaters
|
Eyes, nose, throat irritant
Risk of respiratory infections
|
Ozone
|
Office equipment, air cleaners
|
Chest pain, asthma
|
Polycyclic aromatic hydrocarbons
|
Tobacco smoke, gas cooking
|
Lung cancer
|
Phtalates
|
Adhesives, vinyl floors, wood finishing products
|
Obesity, potentially causing cancer
|
Radon
|
Uranium decaying in soil
|
Carcinogen
|
Volatile Organic
Compounds (VOC)
|
Furniture, carpets, paint, cleaners, solvents, glues, building materials
|
Headaches, fatigue, eyes, nose, throat and skin irritations
|
Figure 3.
List of main indoor pollutants, their sources and adverse effects