Volatile and Semi-volatile Organic Compounds

For a general discussion of indoor volatile organic compounds (VOCs), see the section of this website on VOCs and health. VOCs are present in indoor and outdoor air. Indoor VOCs come from a large number of indoor sources including building materials, furnishings, consumer products, tobacco smoking, people and their activities, and indoor chemical reactions. VOCs 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. Concentrations of VOCs are often reported in units of micrograms per cubic meter (µg m-3) or parts per billion (ppb). VOCs may be odorous and some VOCs are known or suspected to cause a variety of adverse health effects. Formaldehyde is one of the most common indoor VOCs found at concentrations of potential concern to health. The total volatile organic compound (TVOC) concentration is a measure of the total concentration of all measured VOCs. TVOC concentrations have not been demonstrated to be a consistently useful predictor of adverse health effects. Semi-volatile organic compounds (SVOCS) are chemically similar to other VOCs with carbon-based molecular structures but are present both as a gas and, to a substantial degree, sorbed (stuck) to indoor materials and the surfaces of airborne particles. Flame retardants, plasticizers, and pesticides are examples of the indoor sources of SVOCs.

Concentrations of VOCs in schools are available from numerous, generally small, surveys of a few to a few tens of classrooms. Fewer data are available on concentrations of SVOCs in classrooms. Table 1, summarizes key findings. As in other types of buildings, classroom research indicates that the concentrations of many VOCs are much higher indoors than outdoors, indicating the presence of indoor VOC sources [15-21]. Measured concentrations of VOCs vary widely among locations within schools, among schools in the same study, and among studies or study locations. Among the measured VOCs, formaldehyde concentrations were usually highest, tens of mg m-3, relative to other VOCs typically with concentrations less than 10 mg m-3, and sometimes less than 1.0 mg m-3. Concentrations of terpenes were also sometimes higher than concentrations of many other VOCs [16, 17, 22]. Cleaning products are often a predominate source of terpenes. Concentrations of VOCs in schools were typically less than concentrations reported from measurements in homes [23]. A study of sources of VOCs, excluding formaldehyde, in Australian schools [18] estimated that 41% of indoor VOCs were attributable to cleaning products, 23% were attributable to air fresheners, and 21% were attributable to arts and crafts materials. Emissions from building materials were a minor source.

Few studies have assessed associations of VOC concentrations in schools with health outcomes. Four of the studies listed in Table 1 [24-28] include investigations of potential respiratory health effects of higher formaldehyde concentrations in schools. Two of the four studies [24, 26] report statistically significant increases in health effects with increased classroom formaldehyde. In a large cross sectional study in 108 French schools [24], higher indoor concentrations of formaldehyde (median was about 27 µg m-3) were statistically significantly associated with increased rhinoconjunctivitis (nasal congestion, runny nose, red or irritated eyes); however, higher formaldehyde was not associated with past year asthma or past year allergic asthma. In a study of 28 classrooms from 11 secondary schools in Sweden [26], formaldehyde concentrations were generally low (mean less than 5 µg m-3); however, there was a statistically significant increase in rates of current asthma in classrooms with higher formaldehyde concentrations. In another of the four studies [25], this one of 30 classrooms in China, there were increases in airway symptoms and asthma outcomes in classrooms with higher formaldehyde concentrations; however, the increases were not statistically significant. The fourth study [27] found no association of classroom formaldehyde with respiratory symptoms.

For other VOCs, findings are even more limited. One study [24] found statistically significant associations of higher indoor concentrations of acrolein with increases in past year asthma and past year allergic asthma, but not with rhinoconjunctivitis (nasal and eye symptoms). Combustion is usually the dominant source of acrolein, with cooking a potential source in schools. The same study found no associations of classroom acetaldehyde concentrations with health effects. Three studies report statistically significant associations of higher TVOC concentrations with respiratory health effects. Norback et al. [29] found higher classroom TVOC concentrations associated with statistically significant increases in chronic sick building syndrome (SBS) symptoms but not with development of new SBS symptoms. Smedge et al. [26] found higher TVOC concentrations at school associated with current asthma. A study of 76 classrooms from 11 schools in Portugal [28] found statistically significant increases in sick building syndrome symptoms within teachers associated with higher TVOC levels. It appears that there was no control for potential confounders; thus, in this study higher TVOC levels could have served as a proxy for some other exposure or factor causally related to increased symptoms. A single study [27] found higher concentrations of Texanol, a common component of paints, associated with increased nocturnal breathlessness. The same study found higher concentrations of TXIB, a common plasticizer in PVC floor coverings, associated with increases in nocturnal and daytime breathlessness, doctor diagnosed asthma, and current asthma. All of the associations were statistically significant.

One study [30] investigated associations of SVOCs in floor dust, and in particles from air samples, with student cognitive performance. There were statistically significant associations of higher concentrations of tris (2-chlorethylphosphate) in floor dust and in airborne particles, with decreased cognitive performance as measured by the reasoning component of an intelligence test. This compound is a common flame retardant and is also used as a plasticizer.

Table 1 lists three studies that employed data on school VOC concentrations together with estimates of the potency of VOCs to cause cancer. These studies produced predictions of the risks of increased cancer due to VOC exposures at school. For schools in the U.S., Chan et al. [31] estimated a total cancer risk of about 10 per million for a set of 15 VOCs, with formaldehyde the dominant source of risk. Using VOC data from eight naturally ventilated schools in Italy, another study [16], estimated cancer risks that were less than 10 per million in 21 of 23 classrooms, with risks between 40 and 50 per million in two classrooms. Benzene was the biggest source of risk. This analysis did not consider formaldehyde. The third study [19] estimated that the cancer risks of polycyclic aromatic hydrocarbons in airborne particles were less than one in ten million. Cancer risks less than one per million or ten per million are often considered negligible; thus, the typical cancer risks of VOCs in schools can be characterized as small, although in specific cases risks may be of concern. Because VOC levels in homes are typically higher than VOC levels in schools, and because more time is spent at home, the cancer risks of VOCs at school will typically be substantially less than the cancer risk of VOCs exposures at home.

In summary, concentrations of VOCs in schools are typically moderate and less than VOC concentrations in homes. Among VOCs, formaldehyde and terpene concentrations are often highest. Building materials and furnishings are usually a key source of formaldehyde and cleaning products are often a dominant source of terpenes. The available data suggest a possible association of increased respiratory health effects with increased formaldehyde concentrations; however, the data are insufficient for firm conclusions. The estimated cancer risks of VOC exposures in classrooms are on the order of 10 per million, but can be higher in specific classrooms. Among VOCs, formaldehyde appears to be the largest source of cancer risk. Cancer risks below one or ten per million are often considered negligible. Reducing indoor VOC sources and increasing ventilation with outdoor air are the primary options for controlling VOC levels in classrooms. More information on control measures for VOCs is available in the section of this website on VOCs.

Table 1. Results of studies of VOCs in schools.