Rapporteur: Stewart Melvin, Ph.D., Iowa State University
Participants: Dwaine Bundy, Ph.D., Iowa State University
Ken Casey, M.S., Queensland Department of
Primary Industries, AustraliaRon Miner, Ph.D., Oregon State University
Susan Schiffman , Ph.D., Duke University
John Sweeten, Ph.D., Texas A&M University
1. Air content.
Over 160 compounds have been identified in the air associated with swine production facilities. Many have detectable odors at extremely low concentrations. Specific compounds and classes of compounds identified include: mercaptans, sulfides, disulfides, ammonia, amines, organic acids, phenols, alcohols, ketones, indole, and skatole. These compounds arise from the aerobic and anaerobic decomposition of swine wastes.
The air surrounding swine confinement production facilities contains odors, gases, and airborne particles carried from the buildings. Odors emitted from confined swine facilities are primarily derived from the anaerobic decomposition of protein waste material, including feces, urine, skin cells, hair, feed and possibly bedding. Odors are derived from a large number of volatile organic compounds. The principle gases generated from pig production include ammonia, carbon dioxide, hydrogen sulfide and methane. Airborne particles make up an organic dust, which includes endotoxin, possible steroids, and gases adsorbed to the particles. This particulate matter is generated from feed, the pigs, feces, and building materials. Dust particles varying in size may be measured in emissions from swine confinement facilities. At least 50 percent of dust emissions are believed to be respirable. Odor and endotoxins can bond to these particles, but little is known about their fate and dispersion patterns. Climatic conditions, e.g., wind speed, atmospheric stability may determine dispersion patterns of particulates relative to gaseous emissions.
2. Primary odorous substances and their sources.
There is no single compound or small group of compounds responsible for the odor from decomposing swine manure. Odor is typically associated with ammonia, hydrogen sulfide and heavier compounds, perhaps indole and skatole. Swine manure odor consists of a complex mixture of organic compounds. The measurement of easily quantified constituents will not adequately explain odor. This suggests that chemicals interact with more common odorous compounds in contributing to odor. Consequently, amines, mercaptans, organic acids, as well as indole and skatole are likely primary odorous substances. The production of these compounds occurs primarily from the anaerobic decomposition of manure. The expected biochemical breakdown of complex proteins and carbohydrates in pig feed indicates these compounds will be formed either as intermediates or as secondary products in the breakdown process. The formation of these materials in an aqueous solution provides them an opportunity to volatilize prior to further decomposition. The mixture of compounds present in manure will influence the decomposition process and resulting odor.
3. Health effects of swine-related gases and odors on people.
The levels of swine-related gases and odors are considerably lower at neighboring receptors than inside production facilities. However, reports indicate that odors may elicit nausea, vomiting and headache, cause shallow breathing and coughing; upset sleep, stomach and appetite; irritate eyes, nose and throat; and disturb, annoy and depress. Some of the gases from a swine confinement building may be harmful and can cause adverse physiological responses if present in sufficiently high concentrations. Ammonia and hydrogen sulfide are two examples. Methane is explosive when mixed with air. However, the range of ambient concentrations of chemical compounds that cause odor nuisance are much lower than their respective toxic threshold values; odor is rarely associated with chemical toxicity. Agricultural odors have not caused deaths or scientifically identified physical illnesses.
People living near intensive swine operations in North Carolina report significantly more anger, confusion, tension, depression, fatigue and less vigor than people not living near intensive swine operations, as measured by an established Profile of Mood States (POMS) assessment. In addition, persons exposed to swine farm odors have more total mood disturbances than control populations not living near intensive swine operations. There is clear evidence that certain people have had adverse psychological reactions to the development of confinement facilities in their neighborhoods. It is also clear that some of them demonstrated physiological responses.
4. Evidence for airborne microbial, including viral, contaminants that may affect human health.
There are reports of high numbers of colony-forming units per liter of air inside a confinement beef building, a turkey house, as well as downwind from an irrigation sprinkler. Studies have shown microbes 1000 times higher inside production facilities than outside. However, the microbes found generally are not infectious, but may induce inflammation. It is more likely that problems with downwind airborne contaminants are related to allergic reactions to the inhalation of organic dusts. Individual responses to organic dust particles is quite variable and depends on a person's immunological reactivity. Hypersensitivity of certain individuals is frequently associated with some adverse reactions. However, researchers have shown that workers with symptoms are not allergic, and the response is induced by the inflammatory nature of the organic dust.
5. Ammonia and hydrogen sulfide emissions.
Ammonia and hydrogen sulfide have frequently been measured as odor surrogates. Ammonia and hydrogen sulfide concentrations are much more easily measured than are odor emissions. Particularly in research designed to develop odor reduction devices and techniques, a low-cost and quantitative measurement is needed. Ammonia and hydrogen sulfide concentrations serve this function and are indicative of odor intensity so long as a single odor source is being considered. However, researchers and regulatory officials need to recognize that neither ammonia nor hydrogen sulfide concentrations are suitable as a regulatory standard for acceptable odor levels.
6. Acceptable odor exposure levels for the majority of humans.
Odor can be measured both in terms of intensity and frequency of detection. These measurements can be quantified according to accepted standards. People vary in evaluating "offensiveness," which likely depends on the social dynamics of rural neighborhoods where odors occur. In many ways, the social norms of a local community establish an acceptable odor exposure level. Therefore, there is no general standard for odor acceptability based solely on air measurements.
7. Relationship between swine-related methane and carbon dioxide production and the greenhouse effect. Relationship between ammonia loss and acid rain.
Methane is the most abundant organic chemical in the earth's atmosphere. Its level is increasing and atmospheric concentrations have reached the highest levels in geological time. Greenhouse gases are important because they tend to absorb longer infra-red radiation. Methane is a much more potent greenhouse gas than carbon dioxide. Human activity is the major source for methane in the atmosphere. The U.S. is among the five largest emitting countries. Of total emissions, manure-based emissions represent 7.4 percent. The prevalence of anaerobic manure treatment and anaerobic lagoons highlights the role of confinement livestock production as a greater source of emissions than if the same number of animals were being managed in a less intensive manner. However, there is the possibility that global estimates for manure-related methane production are distorted because much of the anaerobic livestock manure exists in areas where temperatures inhibit methane.
Ammonia is a reactive gas and as it diffuses upwards into the atmosphere it readily combines with acidic compounds. In this form, ammonia can be transported over long distances making it a pollutant on a large scale. Deposition of these aerosols has important implications for the critical loads of soil and the health of surrounding vegetation. Ammonia emitted from livestock operations contributes to the problem of acid precipitation and ammonia deposition contributes to excess nitrogen fertilization of natural vegetation and to the leaching of nitrates through soil.
It may become economically and technically possible to reasonably control odor from pig production. Several alternatives to anaerobic lagoons for lowering odor production have been documented. Despite this, anaerobic lagoons remain the primary tool in some geographic areas because of relatively low construction and operating costs. This means that neighbors are being asked to assume a portion of the environmental costs of production.
The existence of larger integrated swine production facilities provides an opportunity to revise design standards. For example, lagoon loading rates were developed to achieve a moderate level of odor in the countryside. These loading rates were published when a typical swine confinement barn contained 600 finishing hogs and the lagoon was relatively small.
If a society plans to respond to global concerns of ammonia and methane as potential contributors to the greenhouse effect, these larger, more technologically sophisticated swine production facilities, offer an opportunity to reduce the impact. However, incentives to reach a higher level of technology effective in addressing odor and greenhouse gas emissions is not necessarily more evident in large facilities than in the small operations.