Residential indoor air quality is not regulated, and the levels of indoor pollution are not widely known. Some sources of indoor air pollution in homes are solvents used in cleaning, building materials, paint, radon, allergens, cooking, smoking, plastics, carpets, and biomass burning for fuel or cooking [1
]. Levels are affected by trends in building design and construction practices, such as reduced ventilation rates, more tightly sealed buildings, and synthetic building materials and furnishings. Solvents involved in renovations and painting in homes have been associated with increased risk of general respiratory symptoms for children under 5 years [1
]. Volatile organic compounds (VOCs) are found in sources such as paints, furnishings, carpets, and household cleaning products. Many can be respiratory and sensory irritants, carcinogens, developmental toxins, neurotoxins, hepatotoxins, and immunosuppressants, and may cause symptoms that manifest as sick building syndrome [6
Most people in the U.S. spend 90% or more of their time indoors [7
]. A recent review of scientific literature on indoor air identified the study of how indoor air affects health as one of the greatest research needs [8
]. The health effects of indoor air pollutants are not fully understood, but indoor air quality has been linked with a wide array of health outcomes including deficits in lung function, chronic respiratory disease, lung cancer, heart disease, developmental disorders, and damage to the brain, nervous system, liver, or kidneys [9
]. Health consequences from indoor air can result from cumulative exposure possibly starting in infancy [13
Children’s health outcomes have been associated with exposure to hazardous chemicals, many of which are present indoors. These health impacts include asthma, behavioral disorders, learning disabilities, autism, cancer, dysfunctional immune systems, neurological impairments and reproductive disorders [14
]. A review of studies on air pollution exposure and sudden infant death syndrome (SIDS) concluded that while more research is needed, there exists suggestive evidence that air pollution affects SIDS [15
]. The authors recommended further research on indoor air quality.
Infants are a unique and important subpopulation to study with respect to indoor air pollution for several reasons. They spend a majority of their time indoors [17
]. Their exposures can deliver higher doses as infants breathe more air per body weight than adults. Their respiratory and other systems are under development. Mouth breathing, which bypasses the filter of the nose, is more common in infants than adults. Mouth breathing may pull air pollutants deeper into the respiratory system, which could result in a different composition of the pollutant mixture at the alveolar level [18
]. Homes of newborn infants are of special interest because parents may consider renovation and redecoration that impacts indoor air quality, such as through indoor painting.
Little research has been conducted on infant exposures to indoor air pollution and consequent health outcomes, partially due to the lack of available monitoring data analogous to that for ambient pollution, the heterogeneity in exposures across homes, ethical considerations regarding human exposure studies for infants, and the challenges of using animal models due to the animal and human differences of gestation periods and developmental stages at birth [19
]. To help address the significant gap in the scientific literature on infants’ exposure to indoor air pollution, we performed a study of indoor air pollution in homes of newborn infants in the New England area of the U.S. using monitoring data to quantify exposures and survey data to assess potential sources of exposures.
The main goal of this research is to expand the scientific literature on indoor air pollution, with a focus on infants’ exposure and source identification in the home. Little research has been conducted on residential indoor air environments for infants compared to the literature on ambient air, occupational indoor exposure, or other studies of exposure in other age groups. To date, most studies of infants and air pollution have been based on ambient pollution, with links to apnea and bradycardia [42
] and infant mortality [43
]. Several studies have investigated indoor air in homes for children. For example, Hulin et al
. measured NO2
, and VOCS in urban and rural homes in France for 51 children (mean age 12.6 years), finding associations with asthma and VOCs [46
]. In Taiwan, the presence of mold in homes of children ages 4–7 years was not associated with biomarkers of allergic response [47
]. Researchers have investigated air in other settings for children, including childcare centers. These studies include measures of phenols in North Carolina and Ohio [48
]; radon, lead, asbestos, and mold in New York State [49
in a Midwestern county in the U.S. [50
]; and ozone in Singapore [51
Studies have examined infants’ health in relation to indoor air pollution from biomass burning in India [52
], Kenya [53
], and Gambia [54
]. One of the few studies to examine infants’ exposure in to indoor air pollution in homes in an industrialized country measured long-term exposure to NOx
, formaldehyde, PM2.5
, and black smoke in homes of 411 infants in Denmark, finding no association with risk of wheezing [55
]. Raaschou-Nielsen et al
. measured PM2.5
and black smoke in homes of 389 infants in Denmark, identifying a variety of sources, such as frying without a range hood, smoking, renovation, and local traffic [56
]. Exposure to indoor pollutants of allergens (e.g., dust mite, cat, dog) and mold have been examined in relation to respiratory symptoms in infants [57
]. A recent study of infants’ homes in Syracuse, New York, U.S., found that levels of PM10
varied substantially across homes and within homes [59
], which is consistent with our results. Higher levels of indoor PM2.5
was associated with infant wheeze. In that study, 68% of participants were smokers, compared to 2.3% of homes with smokers in our study [59
The survey results show that in this limited sample, main sources of indoor pollutants may include renovation, which was conducted prior to or shortly after the infant’s arrival in 66.0% of homes. The potential factors affecting indoor air quality that were present in more than half the homes surveyed are gas stoves, pets, and remodeling of the nursery. General trends in survey results suggest that some populations may be more likely to conduct renovations of the nursery than others, potentially introducing sources of indoor air pollution such as through painting. This result indicates the potential for confounding if those populations (e.g., socio-economic conditions, urbanicity, existing health conditions in the family) are associated with the outcomes of interest in studies of infants’ health.
The limited sample size and narrow variation in participants’ demographics limit the generalizability of this study, as the population is mostly non-Hispanic white, highly educated, and high income. Participants who responded to the recruitment advertisements may have been drawn to volunteer for this study because they previously were interested in environmental issues and therefore may have taken more precautions to limit air pollution in their homes. Future efforts are needed with larger sample sizes to permit study of pollutant levels in relation to various household activities and characteristics, as well as different populations. For instance, our study population had a low reported rate of smoking in the home (3.8%), although environmental tobacco smoke is associated with a range of health outcomes for infants, such as low birth weight [60
Research is needed to assess infants’ exposure to a more comprehensive set of indoor air pollutant measurements, such as biological contaminants including mold, dust mites, pet dander, pollen, dust, environmental tobacco smoke, other size fractions of particles (PM2.5
), specific VOCs, dust, and radon. Data on home activities that could relate to indoor air quality could include detailed information on cooking, smoking, and cleaning. Future work could incorporate the penetration of ambient air pollution into the indoor environment, including differences by season, and information such as information on proximity to various types of roadways. Additional efforts are needed to better understand infants’ exposure to various pollutants in the indoor environment, including techniques to estimate levels with limited monitoring. For example, a microenvironment approach was developed for assessing infants’ exposure to indoor air pollution for respirable suspended particles and CO based on mobility patterns of infants and mothers [63
]. Our findings indicate heterogeneity both within and across homes, suggesting the need for individual-level exposure assessments considering a wide range of settings, including different seasons, regions, demographics, and time-activity information that may affect pollutant levels (e.g., cooking, cleaning, opening windows). The time-activity data are particularly important to help understand the variation and large peaks that occur in pollutant concentrations throughout the day.
This study provides individual-level data that is illustrative of the ranges of pollutant levels that can be found in nurseries, with variation across homes and throughout the day within a single home. Although indoor air quality is not regulated, we observed levels of CO2, VOCs, and PM0.5 that exceeded health-based guidelines, indicating that residential air pollution may pose a health risk for infants. Given the limited sample size of this study, linking these exposure measurements to health outcomes is not appropriate. However, these results provide some of the first measurements of indoor air quality in homes of infants, and are valuable given the paucity of existing data. Understanding exposure assessment can be one of the first steps toward understanding how those exposures affect infants’ health.