Pilot Study of Residential Air Sampling Methods for Endotoxin Lisa Pheatt Abstract In light of research suggesting that endotoxin is an asthma ‘trigger’ and may play a role in childhood asthma development, this study was performed (1) to develop a sampling regime suitable for use in residential environments to measure airborne endotoxin concentrations and (2) to obtain information on the size of particles associated with airborne endotoxin. Indoor air was sampled in six Northern California homes for periods of 24 hours to 3 weeks using at least two particle-size-selective samplers. The samplers included a personal cascade impactor, a Harvard-type impactor, a cyclone/filter cassette, and a filter cassette alone. Each sampler was individually attached to a pump that was acoustically insulated to minimize noise. Phase 1 results suggested that samples of airborne dust of <0.25 mg may not be sufficient to measure endotoxin concentrations above the background of the analytical procedure. This was remedied in Phase 2 by collecting higher air sample volumes and baking the filters before use, a procedure that removes background endotoxin. The endotoxin content of the Phase 2 samples is not yet available, but the mass measurements indicated that cleaner environments may require collection of air sample volumes >3 x 104 m3 to obtain a minimum sample mass of 0.25 mg. This was achieved most efficiently and conveniently with the Harvard-type impactor. Data from Phase 1 indicated that endotoxin concentrations were highest for particles 3.5 and 6.0 µm. This association with particles smaller than 10 µm is significant in assessing the related inhalation exposure to endotoxin as particles <5 µm can be deposited in the alveolar region of the lungs where the body responds differently than to dust deposited in the nose or throat. These findings differ from what has been seen in occupational environments, indicating that more research is needed in residential settings.Introduction Bioaerosols pose significant health risks to agricultural workers and their families in the state of California. Work in fields or processing plants exposes many workers to airborne contaminants that can cause chronic respiratory illnesses, among other health problems. As a result, studies on the environmental health risks for these workers and their families are extremely important and represent a growing field of research (Nieuwenhuijesen et al., 1998). One such bioaerosol is endotoxin, which is a lipopolysaccharide molecule that composes part of the outer membrane of Gram-negative bacteria (GNB). Common examples of GNB include species of Aeromonas, Citrobacter, Enterbacter, Escherichia, and Pseudomonas. GNB and endotoxin are commonly present in agricultural and textile manufacturing settings where they may become health hazards if they are aerosolized during the processing or decomposition of organic materials (Milton, 1999). GNB, which can be ingested via the gut and inhaled into the lungs, was associated with disease as early as 1942, when GNB first were studied as contaminants in drinking water. Subsequent studies suggest that endotoxin itself acts as an immunotoxicant, causing a variety of acute inflammatory responses in exposed persons including fever, increased asthma severity, mucous membrane irritation, chronic bronchitis, byssinosis, and toxic pneumonitis, and hypersensitivity pneumonitis (e.g., “humidifier fever” and “farmer’s lung”)(Milton 1996; Gyntelburg et al, 1994; Olenchock, 1994). On the other hand, some studies suggest that mild exposures to aerosolized endotoxin can actually be beneficial in some cases, as such exposures appear to stimulate the immune system. Endotoxin’s toxic properties have been the subject of numerous studies over the years, however, the connection between any particular endotoxin exposure and respiratory illness is still poorly understood. This problem is a result of many factors, including inconsistent associations between exposure and adverse health affects, limitations on the accuracy of current endotoxin analysis techniques, and only very limited information on the relationship between concentrations of endotoxin in air and settled dust (the latter being an easily obtained material often used for qualitative assessments of endotoxin exposure). Many of these unknowns for endotoxin persist because of underdeveloped sample collection techniques. This study represents an attempt to expand our knowledge of endotoxin and its toxicity by developing and testing a new sampling method which will address two important properties ofthis toxin which have yet to be established — (1) this toxin’s particle size distribution and (2) its presence and behavior in residential settings. Endotoxin has been studied extensively as an occupational hazard. However, few of these studies have investigated the particle size range of this toxin and, of those that have, none agree. Furthermore, as sampling for airborne endotoxin in residential settings is extremely new, no attempt has ever been made to study endotoxin’s particle size range in homes. Particle size is considered important information for any airborne toxin as the hazard associated with the inhalation of a particle is due in part to its size and mass, as this dictates the mechanism and location of its deposition in the human respiratory tract. In this way, establishing the approximate particle-size distribution for endotoxin is a critical element in determining its toxicity or health effects. Previous studies on this topic include Attwood et al. (1986), who reported that 40% of the total endotoxin they collected in swine confinement buildings was between 3.5 and 8.5 µm in diameter, Thorne et al. (1996) who reported a median diameter of 3.1 µm for grain dust and Monn and Becker (1999) who reported a higher concentration of endotoxin in the coarse (>10 µm) particle fraction of outdoor air. The differences in these studies’ results may be due to actual differences in the airborne material in the different study environments or to the use of different collection techniques. Past studies on airborne endotoxin primarily have been conducted in agricultural settings, as these environments tend to have abundant sources of GNB and thus are more likely to constitute a health risk from high endotoxin exposures for workers. However, the presence of airborne endotoxin in residential settings
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