Relation of repeated exposures to air emissions from swine industrial livestock operations to sleep duration and awakenings in nearby residential communities
Introduction
Swine Industrial Livestock Operations (ILOs) are a prevalent source of air pollutants in eastern North Carolina. Today, nearly all of the pork consumed and exported by the United States is produced by ILOs1 and North Carolina is a leading producer, with over 2000 permitted operations and 9 million swine.47 The industry is highly concentrated in the southeastern part of the state,2 where the 2 top-producing counties are also the 2 top-producing counties in the entire United States.48
This context has produced an environment where residential communities hosting swine ILOs can face concentrated industrial air emissions not typically associated with rural areas. Rural areas consistently score poorly on population health indicators,2 and rural communities are experiencing social transitions that create health challenges:3 a shift to corporate agriculture, job loss, outmigration of young and working people, and poorer access to nutritious food.4 Air pollution produced by swine ILOs contains complex mixtures of particulate matter, aerosols, and gasses that can vary by facility, time of day, weather, and season. A large proportion of these air pollutants are produced by lagoon-and-sprayfield systems, which are used for waste management at swine ILOs in North Carolina.5 In this system, wet swine wastes flow through the slatted floors of confinement buildings into open pits where they decompose anaerobically to produce mixtures of microbial metabolites including ammonia and hydrogen sulfide.6 These wastes are sprayed onto adjacent fields to encourage aerobic decomposition, but this process also produces waste aerosols that spread liquid pollutants into the air and groundwater.
In ethnographic research conducted in communities near swine ILOs, neighbors have reported that swine ILO air pollutants interfere with sleeping7 and time outdoors8 but these associations have not been statistically quantified. ILO air pollutant exposures could be linked to sleep disruption through several mechanisms: awakenings could be caused by olfactory or trigeminal nerve excitation by chemical components of the emissions mixture, exposures to the emissions mixture may produce disease symptoms like airway restriction that could increase the risk of sleep apnea or making falling asleep more difficult, or the psychological impacts of uncontrollable malodor could lead to stress and impair activities that enhance sleep. Exposure to ammonia odorants like those found in swine ILO pollutants have long been known to cause awakenings from sleep;7,9 this property has been leveraged in the clinical context through the use of smelling salts.10 Many of the disease symptoms linked to swine ILO air emissions in past research are known to cause sleep impairment. Disrupted breathing can make falling asleep difficult,11 cause awakenings from sleep,12 interfere with outdoor activities,13 and produce psychological stress.14 Respiratory disease symptoms,15 the cultural and psychological meanings of malodor,14 and stress resulting from the inability to control odors could make falling asleep more difficult.
Poor sleep is associated with a host of poor health outcomes that have also been connected to air pollution, including obesity, hypertension, type 2 diabetes, cardiovascular disease, and premature mortality.16., 17., 18., 19. This study seeks to expand the understanding of the transient exposure-response dynamics of ILO pollutant exposures by assessing their impact on sleep. Associations between 2 exposure markers (swine odors and atmospheric hydrogen sulfide concentration) and 2 outcome measures (nightly sleep duration and awakening from sleep) are estimated. We leverage the unique design of the CHEIHO (Community Health Effects of Industrial Hog Operations) study,14,20., 21., 22., 23. which aimed to capture the acute impacts of exposures to hog operation emissions. The repeated measures of exposures and outcomes recorded as part of the CHEIHO study enable each participant to act as his or own control in assessments of potential sleep disruption, eliminating bias due to factors that remain constant over time (e.g., sex, race/ethnicity, co-exposures, and pre-existing conditions) and allowing adjustment for other measured time-varying factors.
Section snippets
Study population
We used data collected as part of the CHEIHO study, a community-engaged project combining environmental health education with mixed-methods qualitative and quantitative research in 16 communities in North Carolina. Potential CHEIHO communities were identified in collaboration with community organizations and had at least 4 residents interested in study participation.
One-hundred and one CHEIHO participants were recruited from 16 North Carolina residential communities hosting industrial swine
Results
Among the 80 eligible adult participants, 65% were female, 85% were Black, and 35% had an odor sensitivity threshold at or below 40 parts per million. Demographic characteristics of the 80 study participants are shown in Table 1.
The distributions of sleep and odorant exposures are described in Table 2. Hydrogen sulfide was above the detection threshold for 8.2% of all study hours and participants reported odors 14.5% of their time awake. Evening outdoor odorants were higher on average than
Discussion
In this study we estimated the effect of exposures to swine ILO pollutants on sleep using 2 measures of odor perception and ambient outdoor H2S concentration. Episodes of nightly hydrogen sulfide exposure and odor, 2 markers of swine ILO pollutant exposures, decreased participants' sleep by 14.3 minutes on average and increased the risk of awakening from sleep by 23%. In the context of chronic daily exposures, these impacts could lead to substantial sleep losses over time.
Observed associations
Conclusion
Ultimately, the night-time ILO pollutant exposures investigated were associated with adverse sleep outcomes, which suggests that emissions reductions and odor abatement are important public health goals. Although we focused on odor and hydrogen sulfide from ILOs, environmental odorants from industrial sources in other areas could also be important for sleep hygiene and the secondary health effects associated with sleep. From a public health perspective, greater community control over local
Declaration of conflict of interest
The authors declare they have no actual or potential competing financial interests.
Funding
This work was funded, in part, by the Intramural Program at the NIH, National Institute of Environmental Health Sciences (Z1A ES103325-01, CLJ) and by the Environmental Biostatistics Training Grant (NIH 2T32ES00701836, NSM).
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