Semivolatile organic compounds (SVOCs) are a subgroup of VOCs that tend to have a higher molecular weight and higher boiling point temperature than other VOCs. A comprehensive review of SVOCs in indoor environments, from which much of the below material is taken, is provided by Weschler and Nazaroff . An additional overview is provided by Xu and Zhang . Compounds considered to be SVOCs have boiling points ranging from 240-260 °C to 380-400°C. Despite these high boiling points, SVOCs such as plasticizers can vaporize from the surfaces of products containing them because they are not "bound" to the materials. They are present partly as gaseous airborne chemicals and partly as chemicals adsorbed on (attached reversibly to, without bonding) indoor surfaces and onto microscopic airborne and settled particles, although those with large molecular weight and low vapor pressures tend to predominate on surfaces and in dust . SVOCs are ubiquitous in indoor environments, as they are released from multiple sources in the home and adsorb to all indoor surfaces.
People are exposed to SVOCs via multiple routes. They inhale air containing gaseous SVOCs or SVOCs adsorbed on airborne particles, they touch SVOC coated surfaces, they ingest dust containing SVOCs (a particularly important exposure route for infants), and the foods they eat contain SVOCs. Also, it has recently been recognized that airborne SVOCs can adsorb directly on the skin and then move into the body .
SVOCs that may be found in homes and other buildings, and also as detectable body burdens of occupants, include pesticides, plasticizers, and flame retardants. It has been calculated that many SVOCs have long persistence indoors. Even if the original sources are removed, SVOCs will persist indoors for weeks or years because all indoor surfaces have become coated with SVOCs. Calculations also indicate that human uptake of SVOCs by absorption on the skin can be much larger than previously thought, potentially equal to or in some cases exceeding intake through inhalation .
Less is known about SVOCs than VOCs in general, not because they are less important, but because they are more challenging to measure. Some SVOCs such as polycyclic aromatic hydrocarbons (PAHs), produced by combustion, have caused human exposures for millennia, whereas the manmade SVOCs have been present only on the order of decades. SVOCs are included as active ingredients in cleaning agents, pesticides, and personal care products, as well as substantial additives in floor coverings, furnishings, and electronic components. Food can also be a substantial, and sometimes, dominant sources of people's uptake of SVOCs. Because they are released slowly from their sources, adsorb readily onto surfaces, and can remain indoors for years after they are introduced, even if the original source is removed, they can be compared to outdoor persistent organic pollutants. The U.S. population has measurable levels in their bodies of more than 100 SVOCs (e.g., 95th percentile values of 360, 270, 90, and 81mg/g creatinine in urine for triclosan, DEHP, BBzP, and DBP, respectively, with body burdens of many others in common use not known, because they are not routinely measured.
The health effects of a specific SVOC depend on its chemical nature and on the degree of exposure, which can occur through a combination of ingestion, respiration, and skin absorption. Individual susceptibility factors can also be important, and much attention has been focused on the developing fetus. Knowledge about effects from indoor exposures to SVOCs is limited. Some SVOCs are known to be toxic, such as dioxins and pentachlorophenol; some are no longer used because of demonstrated or suspected health effects, such as polybrominated biphenyls; and concerns are emerging about potential health effects of others. Health effects now associated with specific SVOCs include allergic symptoms, retarded reproductive development, and altered semen quality with phthalates, and lower birth weight with perfluorooctane sulfonate and perfluorooctanoate. For instance, Hsu  found that allergy or asthma in children was associated in a significant, dose-response manner with increased levels of benzylbutyl phthalate in home dust. A broad and growing concern is about SVOCs with chemical structures that may mimic human hormones and increase or decrease endocrine activity. These SVOCs, called endocrine disrupting chemicals (EDCs), are discussed further below.
A substantial discussion of the occurrence, physical properties, and dynamics of SVOCs in indoor environments, with the goal of understanding human exposures indoors, is provided by Weschler and Nazaroff , along with information on typical U.S. body burdens of many compounds.
SVOCS that are considered to be endocrine-disrupting chemicals (EDCs) include polybrominated flame retardants, phthalates, pesticides, antimicrobials, and polycyclic aromatic hydrocarbons. EDCs can interfere with the "synthesis, secretion, transport, activity, or elimination of natural hormones," which can cause a wide range of developmental and reproductive abnormalities [104, 105]. Scientific observations suggest that, acting through a very wide variety of pathways in the body, EDCs may contribute to cancer, diabetes, obesity, and infertility  as well as autism and attention deficit disorder, although supporting evidence is limited. Exposures to EDCs in utero, when the fetus is developing, are of special concern because the development process may be affected by very small amounts of EDCs. Additional information on the range of EDCs, the evidence for their health effects, proposed mechanisms of action, and the difficulties of assessing the risks, is provided by Casals-Casas et al. .
Many brominated and chlorinated flame retardants, commonly used in many household items and electronics, are SVOCs and have been identified in the body burdens (e.g., in blood or urine) of human populations. They have also been associated with adverse health effects in animals and humans, including endocrine and thyroid disruption, immunotoxicity, reproductive toxicity, cancer, and adverse effects on fetal and child development and neurologic function . Polybrominated diphenyl ethers (PBDEs) and other flame retardants have been banned or phased out by manufacturers because of their environmental persistence and toxicity, but they have been replaced by other chemicals of similar structure but unknown toxicity. A summary of the known toxic effects of commonly used flame retardants is provided by Shaw et al. . A review of animal studies of brominated flame retardants, on the other hand, found that the available animal evidence is not sufficient to document a causal relationship between early exposures and later motor activity effects, and noted that human studies are generally lacking .
A recent review of the literature on indoor exposures and asthma exacerbations  summarized current evidence related to plasticizers and pesticides. For plasticizers, recent studies have demonstrated associations between the presence of plastic materials in homes and increased allergies, respiratory symptoms, and diagnosed asthma [43, 109-111], but have not evaluated effects on asthma exacerbation. No evidence was identified on the relationship of indoor pesticide exposures and asthma exacerbation. The review concluded that there was inadequate or insufficient evidence to determine whether or not an association existed between non-occupational exposure to plasticizers, or to pesticides, and exacerbations of asthma.
For SVOCs overall, there is persuasive evidence that they can cause a variety of adverse health effects, if the exposures are sufficient. The SVOC situation indoors is complex and continually changing. There are multiple SVOCs, multiple routes of exposures to SVOCs, and the timing of SVOC exposures can be important, with in-utero exposures a particular concern for EDCs. There is an ongoing process in which some SVOCs, strongly suspected to pose health risks, are phased out by manufacturers and replaced with new SVOCs with unknown risks. For some SVOCs, foods are considered the predominant 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 uncertain.