Excerpted from : Documented Human Health Effects of Airborne Emissions from Intensive Livestock Operations

We have compiled over 900 articles and abstracts from refereed journals, regulatory documents and conference proceedings concerned with the health effects of airborne emissions from intensive livestock operations (ILOs), including beef and dairy cattle, swine, sheep and goats. Where general indicators of risk to public health have been associated with emissions from other livestock species, with poultry production or with occupational exposures (e. g., pulpwood processing), those data have also been included. Emissions classes considered in the literature review include particulate matter (PM), ammonia (NH3), hydrogen sulfide (H2S), bioaerosols, volatile organic compounds (VOCs) and odor. Public health effects considered in the review include direct respiratory impairment, sensory irritation, synergistic effects of multiple pollutants and psychological effects of nuisance pollution. The depth and breadth of literature on this subject vary substantially among livestock species and appear to be functions of the degree of confinement typical of each. Species generally produced in total confinement (i. e., under roof) have received the greatest attention. In general, time-averaged ambient concentrations of single, high-profile, discrete pollutants (e. g., NH3, H2S) do not appear to exceed exposure thresholds for human health. The human health implications of complex mixtures of pollutants, including PM, bioaerosols and odors, are more difficult to establish and are therefore a fertile area for research. Known occupational health effects of all of the air pollutants considered herein represent a reasonable but incomplete basis for future research into the epidemiological significance of ambient exposures. Even though direct causal relationships between ILO emissions and epidemiological responses in the general public are virtually nonexistent in the refereed literature, the larger corpus of published data from clinical and engineering research suggests that selected circumstantial linkages offer a reasonable basis for further inquiry. Specifically, we found that: 1. The validity and quality of published epidemiological and quasi-epidemiological relationships between (a) ILO odor and (b) psychological responses such as mood and stress need to be evaluated according to olfactometric data (i. e., actual human exposures), distances between sources and receptors and actual weather data; 2. Known associations between agriculturally derived endotoxin and syndromes such as farmer’s lung and byssinosis indicate that property-line and downwind concentrations of endotoxin-laden particulate matter from ILOs may have intermittent (and, perhaps, long-term) clinical significance; 3. The persistence of airborne, Gram-negative respiratory pathogens apart from their hosts or sources is a relatively recent finding and may warrant incremental clinical examination, but we found no compelling association between ILOs and increased pathology (i. e., in the general public) traceable to such microorganisms suspended in ambient air downwind of ILOs; 4. Synergistic effects of NH3 and PM on the respiratory health of animals invite further inquiry in the context of human health; 5. Occupational exposures to the full range of ILO emissions, in general, are often significant in fully confined livestock facilities and, to quite a lesser extent, in open-air facilities; and Auvermann and Rogers, 2000 3 6. Where respirable, secondary PM has been linked with public health effects, the contribution of ILOs to regional NH3 enrichment may be an indirect and partial cause. However, an assessment of ambient concentrations and formation kinetics in relation to (a) atmospheric residence times and (b) credible apportionment of NH3 sources is needed before epidemiological study of ILO neighbors is justified in the context of respirable, secondary PM. Motivation and General Approach The idea that air pollution arising from confined livestock production may impair the health and quality of life of neighbors and nearby communities has potentially explosive implications for the economic and social forces that drive the growth and incremental dislocation of the ILO industry. As is the case with any industry whose expansion poses unknown environmental risks, stakeholder groups who elect to play a role in shaping environmental policy with respect to that industry are numerous and diverse. That diversity, moreover, is expressed in several dimensions (social, political, economic and scientific) as stakeholder groups begin with unique presuppositions in each of those dimensions. Groups whose presuppositions contrast most starkly find it difficult to establish a solid foundation for cooperation in the development of mutually beneficial public policy. To the extent that such cooperation is vital to long-term sustainability of both industry and community (we assume that it is), credible science can play a modest but important role in reducing or circumventing those fundamental barriers to cooperation. We recognize at the outset, therefore, that public health authorities and livestock producer associations in Canada operate with vastly different mandates (i. e., from their respective constituencies) and with vastly different scientific presuppositions that express those mandates. In general, the public health official is concerned with discovering and exposing possible risks to public health without regard to the economic implications of his findings. If he is to err, he will elect to err on the side of exposing risks that may not be real so that the public is, in effect, overprotected. In this frame of reference, causation may appear to take a back seat to association, at least when considering whether to go public with preliminary findings. The public health agency’s mandate requires it. (Clearly, subsequent decisions about allocating scarce public resources demand a greater degree of confidence in causal mechanisms.) Typically, regulatory agencies are required by statute to establish protective thresholds in response to public and political demand, even when little data exist to support such thresholds. This pressure to set standards in the face of little supporting scientific data and the inherent “uncertainty” typically results in extremely conservative standards. The regulators rely on the affected industries and further research to provide the dose/response data needed to reduce the overall uncertainty associated with the standard(s). As such, it is the industries’ best interest to take an active part in the development of reliable dose/response relationships and then to develop risk management plans to address those issues and to protect the public and industry workers. In virtually all cases, the unknown is perceived to pose a much greater risk than the known. So it is desirable to bound the true risk and communicate that risk to the public, regulators and workers. The livestock producer association, and the agricultural research community more generally, tend to focus on research whose purpose is to identify inefficiencies, develop technologies and clarify causality in search of competitive advantage in the marketplace. Resource allocation is among the first questions asked by agricultural enterprises, who cannot afford to waste resources developing knowledge that has little potential for immediate return or that has great potential for accelerating losses. The agricultural community, composed of individuals whose livelihood depends on sustainable profit growth, demands such a conservative outlook. (Clearly, agricul-tural interests actively recognize that the social and ethical implications of their activities and products are also critical to the sustainability of their enterprises and communities.) In the immediate context of health effects from ILO emissions, the fundamental conflict between these competing presuppositions or frames of reference is strikingly clear. The public health official must not narrow his focus to the point that he misses an unanticipated threat to public health. The agricultural community must not cast its research net so widely that it fritters away its profit margin on fruitless Auvermann and Rogers, 2000 4 endeavors or inquiries in which the mere statement of a hypothesis would be socially explosive (and, hence, economically disastrous to the industry). Resolving the conflict between the competing views has both technical and social dimensions, and those dimensions are somewhat interrelated. Still, although science cannot solve this central conflict, it can and must inform both the technical and social dimensions of the solution from the outset. Further, it must embrace all of the competing presuppositions in an objective and unbiased way if its influence is to be sustained. This literature review is not intended to be the final word in the design of a cooperative research agenda. Our goal in this literature review has been simply to present the modern state of knowledge concerning the health effects of airborne emissions from ILOs in a comprehensive (certainly not exhaustive) and objective way that: 1. Informs the principal stakeholders; 2. Embraces their presuppositions; 3. Identifies key scientific gaps; and 4. Provides a basis for further discussion and cooperative action. In recognition of the ILO industry’s need for scientific certainty, we have emphasized conclusive, refereed literature when evaluating etiology, emissions characterization and dose/response relationships. Where hard and comprehensive epidemiological evidence is lacking but components of the exposure/dose/response continuum are individually compelling, however, we have drawn more liberally from monitoring surveys, agency reports and conference proceedings in an effort to outline credible causal pathways deserving more attention. Because of the huge compendium of reference materials that have been assembled (nearly 1,000), we have made no attempt (a) to summari