Peter S Thorne

Bioaerosols are airborne compounds or microfragments from plant or animal matter or from microorganisms but also comprise whole microorganisms that are either dead or alive. Exposure to these agents may cause infectious diseases, allergic diseases, acute toxic effects, respiratory diseases, neurological effects, and possibly cancer. Respiratory symptoms and disease are the most common health effects associated with noninfectious bioaerosols and include asthma, hay fever, organic dust toxic syndrome, hypersensitivity pneumonitis, and chronic bronchitis. Bioaerosol exposure has also been demonstrated to adversely affect lung function and might play a role in sick building syndrome. Paradoxically, indoor exposure to moderate levels of bioaerosols has been suggested to reduce the risk of developing allergies and allergic asthma in early life. In this article we present an overview of the health effects associated with bioaerosol exposure in both the indoor and occupational environment. We also describe the major agents assumed to play a causal role in the development of bioaerosol-related health effects.

Airborne bacteria and their associated immunomodulatory ligands, best exemplified by endotoxin, are present in bioactive concentrations in many occupational and some non‐occupational environments. Especially high concentrations are found in agricultural settings and in industrial operations handling or processing wet organic matter. Human exposure to these agents induces a variety of respiratory conditions including asthma, asthma‐like syndrome, hypersensitivity pneumonitis, organic dust toxic syndrome and pulmonary infections. Endotoxin is an integral component of the bacterial cell membrane and is well‐recognized as a potent inducer of lung inflammation. However, low‐dose exposure has also been shown to reduce the potential for development of allergic rhinitis and eosinophilic asthma. This chapter presents a critical examination of current knowledge of concentrations and exposures to airborne bacteria and endotoxin in over twenty‐five environments. It describes the resulting burden of disease ascertained through epidemiologic studies conducted worldwide. Included in the chapter are detailed methods for the assessment of exposures to endotoxin. New science relating to occupational exposures to the Archaea are also presented along with molecular methods for their identification and quantitation.

Industrial livestock production facilities emit to the air noxious gases, vapors, bioaerosols, and particulate matter. These compounds emanate from livestock buildings, open waste storage reservoirs, and sites of manure land application. Some effluents act as greenhouse gases, whereas others present respiratory health hazards to the livestock facility workers. Vapor-phase toxicants and bioaerosols can be transported
via the air to neighboring dwellings and pose a public health risk. Odors associated with anaerobic microbial decomposition of manure contain over 300 identified chemicals and can be particularly offensive. Airborne microorganisms can be infectious or noninfectious or can act as allergens. When inhaled, bacterial endotoxin and fungal glucans act as ligands for pattern recognition receptors to trigger innate immunity producing inflammatory lung disease. Evidence is mounting that excessive nontherapeutic use of antibiotics is giving rise to resistant bacteria that are airborne in the barns and are emitted and carried downwind from animal houses. Large setbacks from residences or public use areas, application of biofilters, use of aerobic manure digestors, and proper manure handling are available controls that reduce the risks of community exposures to toxicants from livestock production facilities.

During times of flooding, waterborne hazards are obvious, but few think about the dangers that might be drifting through the air. Yet floods produce airborne hazards that often linger long after the flooding has ended. Floods produce airborne chemical health hazards when previously contained toxic substances are released into the environment, and microbial hazards when post-flood conditions promote the growth of microorganisms. Some airborne hazards, like carbon monoxide, are widely recognized. Others such as spores from the moldAspergillus nigermay be unfamiliar to the general public. Exposure to airborne hazards can occur in a variety of manners. Toxic agents

Although many studies on asthma have been conducted in farming populations, no longitudinal studies have been published so far. Smoking, work in pig barns, and crop farming together with exposure to endotoxin and quaternary ammonium have been described as environmental risk factors for self-reported asthma and/or wheeze in cross-sectional studies. The prevalence of selfreported asthma has been found to range from 0.7% in female greenhouse workers to 21% in Danish smoking female farming students. Exposure in farming is diverse, but dominated by organic dust containing high amounts of compounds known to trigger the innate immune system. This is confirmed by a wide range of human experimentation where naïve persons have been introduced to swine confinements. Cross-sectional data suggest a protective effect of farming on allergy. However, differences in the diagnostic procedure and the predominantly wheezy asthma type in farming concomitant with a lower rate of allergic asthma makes the comparison difficult. Furthermore, healthy worker selection, misclassification, age differences, difference in time of study and small study populations, resulting in low statistical power, might be factors explaining the findings. Welldesigned longitudinal studies of the incidence of carefully defined phenotypes of asthma and risk factors are needed to clarify the risk of asthma, or wheezy phenotypes related to farming.

With the transition to increasingly larger swine production facilities, nearby residents have voiced concerns about environmental contamination, odor, and adverse health effects. The goal of this study was to evaluate outdoor airborne concentrations of am38monia, dust, and endotoxin in the environment near four types of swine production facilities and one control farm with no livestock. Dust and endotoxin were detected at a distance of 60 meters outside of facilities but generally, concentrations were below limits of accurate detection. The mean (and standard deviation) for outdoor ammonia concentrations were: 0.251 (0.064) ppm-large confinement; 0.086 (0.091) ppm-medium confinement; 0.214 (0.160) ppm-small confinement; 0.139 (0.188) ppm-small conventional; less than 0.004 ppm-control farm. While the airborne concentrations of ammonia measured outside the production facilities were below current occupational health standards, it is possible that ammonia could be a physical irritant in combination with other exposures, or it could serve as a cue capable of initiating a physical response. Furthermore, ammonia may serve as a surrogate measure for other gases (sulfides) emitted by these facilities.