Common household activities are associated with elevated particulate matter concentrations in bedrooms of inner-city Baltimore pre-school children

Abstract

Asthma disproportionately affects inner-city, minority children in the U.S. Outdoor pollutant concentrations, including particulate matter (PM), are higher in inner-cities and contribute to childhood asthma morbidity. Although children spend the majority of time indoors, indoor PM exposures have been less extensively characterized. There is a public health imperative to characterize indoor sources of PM within this vulnerable population to enable effective intervention strategies. In the present study, we sought to identify determinants of indoor PM in homes of Baltimore inner-city pre-school children.

Children ages 2–6 (n=300) who were predominantly African-American (90%) and from lower socioeconomic backgrounds were enrolled. Integrated PM_2.5 and PM₁₀ air sampling was conducted over a 3-day period in the children's bedrooms and at a central monitoring site while caregivers completed daily activity diaries. Homes of pre-school children in inner-city Baltimore had indoor PM concentrations that were twice as high as simultaneous outdoor concentrations. The mean indoor PM_2.5 and PM₁₀ concentrations were 39.5±34.5 and 56.2±44.8 μg/m³, compared to the simultaneously measured ambient PM_2.5 and PM₁₀ (15.6±6.9 and 21.8±9.53 μg/m³, respectively). Common modifiable household activities, especially smoking and sweeping, contributed significantly to higher indoor PM, as did ambient PM concentrations. Open windows were associated with significantly lower indoor PM. Further investigation of the health effects of indoor PM exposure is warranted, as are studies to evaluate the efficacy of PM reduction strategies on asthma health of inner-city children.

Introduction

Asthma is the most common chronic disease of childhood in the United States (ALA, 2006). For reasons that are still not entirely clear, inner-city minority children are disproportionately affected by asthma (CDC, 2006). Asthma is not only more prevalent among this population but mortality is higher and morbidity is more severe, including higher rates of emergency department visits and hospitalizations (ALA Epidemiology and Statistics Unit, 2005).

Multiple factors have been suggested to explain the urban and racial disparities in asthma health, including higher exposure to ambient air pollutants. Ambient pollutants, such as airborne particulate matter (PM) exposure, have been linked to more severe respiratory symptoms and decreased lung function among asthmatics, as well as increased mortality in the general population (Delfino et al., 2004; Mar et al., 2004; McConnell et al., 2003; Samet et al., 2000). It is notable that racial and ethnic minorities are more likely to live in the inner-city, where ambient PM concentrations are higher than in other more suburban settings (ALA Lung Disease Data in Culturally Diverse Communities, 2005). In addition, it has been shown that indoor PM concentrations in inner city homes are more than three times greater than suburban home environments (Simons et al., 2007). Differences in exposure to indoor as well as outdoor PM may be partially responsible for increased inner-city asthma burden.

While the evidence for the effect of ambient PM is substantial, there is now also growing evidence for the effect of indoor PM on asthma health. For example, small panel studies in children have found that exposure to elevated indoor PM concentrations is associated with lower lung function (Koenig et al., 1993; Trenga et al., 2006). While these latter studies of the effect of indoor PM on asthma have not focused on racial and ethnic minorities, this evidence suggests that indoor PM may have harmful effects on the respiratory health of young children generally. Further evidence underscoring the importance of indoor air as a highly relevant exposure for young children is that most Americans, including young children, spend over 85% of their time indoors (Klepeis et al., 2001). Thus, indoor PM exposure likely contributes more to the personal exposure of pre-school age children than outdoor PM exposure.

There have been several large studies investigating particulate matter in U.S. homes (Breysse et al., 2005; Wallace, 1996; Wallace et al., 2003). However, substantial gaps still exist in our understanding of the determinants of PM in the homes of very young, minority children. Most of the study populations were comprised of adults and older children living in cities throughout the U.S. (Wallace, 1996), and few of these studies focused on minorities. One of the more recent studies that included inner-city residents enrolled graduates of an environmental intervention study which means that the results may not represent the natural state of inner-city homes (Wallace et al., 2003). These studies all found smoking to be a major predictor of indoor particulate in the homes of smokers. Cooking activities were also found to be significant contributors to PM concentration in a subset of these studies (Ozkaynak et al., 1996; Wallace et al., 2003). Whether the results pertain to the especially vulnerable subset of pre-school inner-city minority children is unclear.

Given the impressive excess burden of asthma on young, inner-city children, there is an urgent need for strategies to limit potentially harmful exposures. Because the indoor environment is unique compared to the outdoor environment (Wallace et al., 2003) and because young children spend most of their time indoors, exposures from indoor environments in inner-cities warrant further investigation. In order to design effective strategies to limit indoor PM, it is essential to understand sources and determinants. To fill this gap in our knowledge, we conducted a study to identify predictors of in-home PM exposure in young inner-city minority children, using information from daily accounts of activities that occurred in the homes and simultaneous environmental PM monitoring.