Volatile Organic Compounds
Volatile Organic Compounds (VOCs)
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, people and their activities, 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. Indoor air typically contains many VOCs, but most are present at low concentrations. Formaldehyde is one of the most common indoor VOCs. VOCs may be odorous and some VOCs are known or suspected to cause a variety of adverse health effects.
The main findings of related scientific research are as follows:
Sensory irritation symptoms, which include irritation of eyes, nose, throat, and skin, are frequently reported by occupants as linked to their periods of occupancy in specific buildings. There is significant and increasing evidence that VOCs sometimes cause sensory irritation symptoms; however, the current evidence is insufficient for firm conclusions. Most individual VOCs are probably not present at a sufficient concentration in the air of typical buildings to cause sensory irritation symptoms themselves. Formaldehyde is the best documented exception to this. Mixtures of multiple VOCs, which can include specific highly irritant VOCs that are produced by indoor chemical reactions, appear likely to be sources of irritation in buildings at some times. Initial evidence is appearing that concentrations of some specific VOCs may be related to the occurrence in buildings of a broader set of symptoms, such as respiratory symptoms, headaches, and fatigue, sometimes called Sick Building Syndrome symptoms. The actual mechanisms for these possible effects are unknown.
There have been four substantial review articles addressing the association of higher concentrations of VOCs in indoor air with allergies, asthma, and related adverse respiratory health symptoms. Three out of four reviews, and a majority of the more recently published papers, find significant evidence of linkages between some VOCs and these health effects. The evidence of a linkage of formaldehyde with allergies, asthma, and respiratory effects is most extensive. However, many related uncertainties remain and this linkage remains controversial.
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 (that is, to cause cancer in humans). Estimates of the magnitudes of cancer risks posed by indoor air VOCs vary widely, with most estimates indicating that total excess individual risks for developing cancer with lifetime exposures for specific VOCs are between one in ten thousand and one in one million. Given the uncertainties in cancer risk assessment, particularly the uncertainties of extrapolating from high concentrations to typical lower indoor concentrations, or from animals to humans, as well as the limited available information on the effects of VOC mixtures, and the effects of VOCs on susceptible populations, the magnitude of the cancer risks posed by indoor VOCs will continue to have a high level of uncertainty.
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. Because cleaning activities will often simultaneously increase exposures to VOCs and non-VOC pollutants, the links of cleaning work to adverse respiratory health effects are not necessarily a consequence of cleaning-related exposures to VOCs.
Semivolatile organic compounds (SVOCs) are a subgroup of VOCs that tends to have a higher molecular weight and higher boiling point temperature than other VOCs. All indoor VOCs are present partly as gaseous airborne chemicals and partly as chemicals adsorbed on indoor surfaces and onto microscopic airborne and settled particles. For many SVOCs, only a small fraction is present as a gas in the air unattached to particles, but a large fraction is present on surfaces and particles. Some of the key indoor sources of SVOCs are pesticides, plastics such as vinyl flooring, and flame retardant chemicals contained in building materials and furniture. Overall, there is persuasive evidence that SVOCs can cause a variety of adverse health effects, if the exposures are sufficient. The SVOC situation is complex. There are multiple SVOCs and multiple routes of exposures to SVOCs. The timing of SVOC exposures can be important, with in-utero exposures a particular concern. There is an ongoing process in which some SVOCs strongly suspected to pose health risks are phased out and replaced with new SVOCs with unknown risks. For some SVOCs, the food pathway and incidental ingestion of dust are considered the dominant source of exposure. At present, the extent of health risks from indoor airborne SVOCs, and from people’s contact with indoor SVOC-contaminated surfaces, is quite uncertain. However, unlike other VOCs, many SVOCs are persistent and, as with flame retardants, accumulate in the body.
Indoor chemical reactions in office buildings occur spontaneously between oxidants such as ozone and various common indoor chemicals in indoor air or on indoor surfaces. The products of these chemical reactions, only some of which have been identified, have been hypothesized to cause sensory irritation of eyes and airways or skin irritation. Overall, however, the current evidence is too sparse to draw conclusions about the health consequences of indoor chemical reactions.
While there are many uncertainties about the health risks of indoor VOCs and SVOCs, the evidence of health risks is clearly sufficient to warrant that precautionary measures be taken to limit VOC and SVOC exposures. Eliminating or limiting the indoor sources of VOCs and SVOCs is the first option to consider. In some cases, sources can be easily eliminated or reduced through behavior changes or product substitutions, while in other cases source reduction measures are complicated and require tradeoffs. Outdoor air ventilation is the other main option for reducing concentrations of VOCs released from indoor sources. When more outdoor air is provided, either through a mechanical ventilation system containing fans, or by increased opening of doors and windows, the indoor air concentrations of VOCs released from indoor sources will decrease. Increased ventilation is often easier to apply than source control, and ventilation simultaneously reduces concentrations of many VOCs; however, ventilation in many situations increases a building’s energy use and will often result in smaller reductions in indoor VOC concentrations than can be achieved with VOC source control. One reason for this is that, for some compounds like formaldehyde, benefits of increased ventilation can be partly offset by increased emissions. Increased ventilation will not be highly effective in reducing airborne concentrations of SVOCs (the higher molecular weight VOCs that are present mostly on indoor surfaces).
Last updated September 2017