Student Clinic

Controlling Odor and Gaseous Emission Problems from Industrial Swine Facilities: A Handbook for All Interested Parties

2.0 ODORS AND GASES: AN OVERVIEW

2.1 Distinction between Odors and Gases

Although many people refer to swine odors and gases interchangeably, there is a difference between these two terms, and there is no known correlation between swine odors and the specific gases emitted from swine facilities. The term "odor" refers to the complex mixture of gases, vapors and dust that result from the anaerobic decomposition of swine manure. The characteristic smell of ammonia and the familiar "rotten egg" odor of hydrogen sulfide gas are often associated with swine facility odor emissions. However, the anaerobic process of manure decomposition associated with industrial swine odor also gives rise to approximately sixty other volatile compounds. These substances include fatty acids, organic acids, alcohols, aldehydes, carbonyls, sulfides, esters, mercaptans, amines and nitrogenous compounds, which often contribute far more offensive odors than ammonia or hydrogen sulfide (Swine Odor Task Force [SOTF], 1995). Many of these odorous compounds are carried by swine dust and other airborne particulates, including swine dander, bedding dust and manure dust, which also contribute to an odor plume. In addition, these particles are capable of carrying bacteria and other microorganisms that may originate in a large swine facility. Thus, swine odors are quite complex, making it not only difficult to determine the specific substances that are contributing to the offensive smell, but also problematic in regulating these ambiguous mixtures.

On the other hand, the term "gases" refers solely to the specific gaseous compounds that are emitted from swine facilities. Some of these gases may be constituents of an odor plume; however, unlike odors, these compounds--in their pure forms--are neither combinations of compounds nor carriers of microorganisms and other particulates. Contrary to odors, many gases are also odorless and tasteless, making them seem benign since they are difficult to detect with the human nose. Ammonia (NH₃), hydrogen sulfide (H₂S), methane (CH₄) and carbon dioxide (CO₂) constitute the majority of gaseous emissions from swine facilities (Taraba and Piercy, undated). These gases are also the most important compounds generated because of both their hazardous properties and their potential for causing environmental damage.

It is important to recognize the distinction between odors and gases because they not only are measured and regulated separately, but also have different effects on human and environmental health. For example, odors are often a nuisance to nearby residents of swine facilities; however, many researchers argue that it is the specific gases of manure decomposition that contribute to severe adverse public health and environmental effects. Moreover, gaseous constituents of odors, which are targeted for regulation due to their offensive smell, are not necessarily the same gases that contribute to health and environmental problems (Thu, 1998). Thus, since 99 percent of the research efforts addressing swine emissions focus on the odor problem rather than the specific gas problems, many of the gaseous culprits of public health and environmental problems are bypassed in the research process.

Furthermore, it is also necessary to delineate the differences between the actual odor intensity of specific gases and their respective gas concentrations. Odor intensity is a measure of gas detection by the human nose, while gas concentration measurements denote the actual concentration of the gas in the atmosphere (Schmidt and Jacobson, 1995). The relationship between these two parameters varies among different gases. For instance, odor intensity and gas concentrations of ammonia are positively correlated, yet do not follow a 1:1 correlation ratio; thus, reductions in gas concentrations do not translate into the same reductions in odor intensity. This phenomenon was observed in a 1991 study where it was found that although ammonia gas concentrations were completely reduced when manure storage units were covered, odor intensity of ammonia was only reduced by 72 percent (Schmidt and Jacobson, 1995).

Although it is important to differentiate between odors and gases, both substances are contributing to the decreased quality of life that is experienced by neighbors and workers of large-scale swine facilities. Thus, this section addresses both odors and gases, including a discussion of the following sub-topics: sources, measurement techniques, public health implications and effects on ecosystems, local economics, and property values.

2.2 Odors

2.2.1 Odor Sources

Odors emanating from large-scale swine facilities originate from four main sources: swine buildings, waste storage and treatment processes, land application practices and carcass disposal areas.
 

Swine Buildings

Swine buildings contribute approximately 35 percent of the odor emissions associated with commercial swine production (Jacobson, 1995). In comparison to traditional swine housing on smaller-scale farms, swine buildings utilized in industrial swine facilities are more enclosed and tightly constructed (www.inform.umd.edu). These facilities also house a higher density of animals, 24 hours a day from "semen to cellophane".

There are two main sources of odors within these buildings: the actual hogs, and the manure and urine, which is excreted at two to four times the daily rate of a 70-kilogram man. In the tight confines of these buildings, swine become soiled with manure, urine and feed dust, their body heat radiating the odor of the culmination of these substances. In most large-scale facilities, the manure and urine that do not collect on the swine pass through slatted floors into a holding area beneath the building, where they remain until the next removal date. These holding areas often generate a large portion of the odors associated with housing facilities, especially when ventilation devices are utilized, pumping the odorous by-products of decomposition outdoors. In addition, when dust from dander, feed and manure is neglected, coating walls and ventilation systems, nearly every surface of the facility releases odors, which may escape from swine buildings in a concentrated dose (SOTF, 1995).

Waste Storage and Treatment Processes

Waste storage facilities account for approximately 20 percent of industrial swine odors (Jacobson, 1995). In most cases, swine wastes are washed, pumped or scraped from beneath housing structures and stored in outdoor lagoons. During the start-up phase of a new lagoon, several offensive odors are produced until decomposition processes reach an equilibrium status. Mature, well-managed lagoons are capable of releasing minimal odors; however, if a mature lagoon is mismanaged, with excessive amounts of new raw waste being added too rapidly, a relatively severe odor problem may develop. Furthermore, when manure wastes are extracted from lagoons for land application, strong odors may ensue if the waste is extracted from the deeper, anaerobic layers of the lagoon. Thus, extraction from the uppermost, aerobic layer of the lagoon is the preferred technique in this process (SOTF, 1995).

Land Application

Due to the rich nutrients present in swine excreta, manure wastes are often utilized as fertilizers for pastures, crops and woodlands. In this process, liquid manure is drawn from the surface of lagoons and distributed across the area of destination. Yet this process is often performed during the summer months; thus, with heat and humidity promoting the release of odorous compounds, land application practices contribute approximately 40 percent of the swine odor problem (Jacobson, 1995). As stated above, liquid manure drawn from the surface of lagoons generally does not create a severe odor problem when used for land application. However, if the deeper anaerobic sludge of manure lagoons is spread across land, highly volatile compounds rapidly rise into the air, creating offensive odors for downwind bystanders. In addition, the odor problem associated with land application is oftentimes aggravated when the application process is poorly managed. For example, even if surface lagoon manure is spread across land, the odor can become severe if too much manure is spread on one occasion (a practice occurring when mature lagoons are reaching maximum capacity).

Carcass Disposal Areas

Due to disease, crowding, and other mass production techniques utilized by industrial swine facilities, thousands of pigs meet their demise each month before they are finished and ready for slaughter, introducing the problem of carcass disposal. According to the Swine Odor Task Force from North Carolina, a farrow-to-finish operation supporting 1,000 sows produces nearly 40,000 pounds of dead swine each year. In North Carolina, swine carcasses are disposed of in the following ways: landfills, mass on-farm burial sites, incineration or rendering for future use (SOTF, 1995). However, decomposing carcasses can emit nauseous odors in the storage and transport processes that precede these disposal methods. Furthermore, the risk of disease transmission is inherent if hogs that died from infections are not disposed of properly.

2.2.2 Odor Measurement

Due to the complex composition of odors, variable sources, environmental factors, and varying human perceptions of offensive smells, it is very difficult to measure swine odors and determine a reasonable, objective threshold limit for swine odor emissions from large-scale operations. However, odor measurement can provide a scientific basis for odor control policy, with regard to site selections, complaint resolutions, and nuisance litigation (Sweeten, undated). Therefore, it is imperative that odor measurement protocols be developed and utilized in assessing odors emitted from large-scale swine operations. Odor measurement standards also can be utilized to make comparisons between different facilities, such that facilities that do not meet the standards can learn from the odor management techniques implemented by facilities that do adhere to established standards.

A number of electronic devices have been developed and tested to measure odors. In Australia, scientists have experimented with an instrument that measures para-cresol, an agent that potentially could be an 'indicator chemical' in swine odor plumes. However, scientists in the United States and Western Europe contend that no reliable 'indicator chemicals' are present in odor plumes as complex as those produced by the decomposition of swine manure (SOTF, 1995). Thus, since no proven electronic device for odor measurement exists, the human nose is the best available detector. Several sensory methods involving the human nose have been developed and used on a widespread basis. The major methods are absorption media, olfactometry and scentometry (Sweeten, undated). Each of these techniques requires the following five steps: sample collection, sample dilution and presentation to panelists, indication of response, interpretation of response and presentation of results.

Absorption Media

The absorption media technique utilizes dry cotton swatches to capture odor samples from swine facilities at different observation sites. The sample swatches are then presented to a group of panelists, along with two control swatches, and the panelists are instructed to determine which swatch is different from the others. This technique is helpful in determining "the effectiveness of alternate manure handling methods and odor reduction practices in swine buildings, in terms of relative odor strengths and offensiveness" (Sweeten).

Olfactometry

The most popular olfactometry method involves the use of a dynamic olfactometer device, which samples and analyzes odors onsite, without the use of sample storage. This instrument takes in an odorous air sample along with a stream of non-odorous air (charcoal-filtered air or bottled breathing air), which is used to dilute the sample odor or provide relief-breathing to panelists (Sweeten, undated). Various dilutions of the odor sample are then smelled by a group of 4 to 16 panelists, who indicate the dilution at which odor is detected. A dilution-to-threshold value is then established using the dilution that was first detected by the majority of the panelists. This technique works well in comparing different odorous air samples; however, a drawback to dynamic olfactometry is that a standard design for dilution tools has not been established. Therefore, different researchers and labs produce dissimilar results for the same odor sample. In addition, olfactometers can cost between $15,000 and $40,000 and an odor panel must be trained and compensated for their work, making this method of odor assessment quite costly.

Scentometry

A scentometer, which is also used to determine a dilution-to-threshold for odors, is a hand-held device, which can be used for direct field measurements of threshold dilutions. The device consists of "a small plexiglass box, two glass nose pieces, two activated carbon filter chambers and a series of graduated intake orifices" (Huey, 1960). Varying ratios of odorous ambient air are drawn into the device, passed through the carbon filter and introduced to one panelist through nose pieces, which are designed to fit into the panelists' nostrils with an airtight seal (Sweeten, undated). The panelist then indicates which ratio of odorous air to filtered air is detectable and the identified ratio is reported as the dilution-to-threshold value. Unfortunately, this method of odor measurement requires the panelist to be present at the observation site; therefore, bias may be introduced if panelists unknowingly anticipate the odor or become immune to the odorous ambient air. In addition, scentometry involves only one panelist; thus, the results are difficult to verify (SOTF, 1995). Perhaps a future area of study in scentometry could entail the development of a multi-person scentometer. This would enable verification and averaging of results.

2.2.3 The Development of Thresholds Outside of the United States

Although odor measurement has proved to be complex and difficult, European countries still favor the use of odor thresholds and promote the development of a standardized protocol for odor measurement. In Germany, determined thresholds have even been effectively used in lawsuits against odor offenders. Furthermore, researchers in the Netherlands have achieved some degree of measurement standardization with approximately ten labs applying the same procedures for measuring odors (SOTF, 1995). The Netherlands also has implemented an ecolabel system for swine production facilities that do not exceed threshold values for ammonia emissions. This system is based on the results of European studies, which contend that reducing levels of ammonia significantly reduces the severity of odors, even though ammonia is generally not the most offensive compound within the odor plume. Perhaps this practice may be the most effective method of odor control, because it bypasses the complexities of establishing odor thresholds, relying instead on gas thresholds, which are more easily measured and more reliable.
 

2.2.4 Bioaerosols in Odor Plumes

Other elements of odor that are also difficult to measure are bioaerosols present in an odor plume. Bioaerosols are defined as biological particulates "with biological action indicated by viability, infectivity, allergenicity, toxicity, or pharmacological activity" (Cox and Wathes, 1995, in Homes, 1995). They are generated from the fragmentation and subsequent aerosolization of biological materials including dander, feed, excreta and bedding. Bioaerosols are likely to be a constituent in odor plumes emitted from large-scale swine facilities.

The pressing issue associated with bioaerosols is that evidence suggests that microbial pathogens of swine can be carried and spread by dust or nuclei present in the aerosols. Moreover, these organisms could be transmitted downwind via different air patterns, depositing on a final destination, several hundred meters away from the source. Thus, there is concern among pork producers and neighbors that bioaerosols present in odor plumes may have occupational, swine, and human health implications (Homes, 1995).

2.2.5 Public Health Implications of Swine Odor

Odor and Human Health in General

Minimal data is available concerning the public health effects of odor because most odor studies investigate the impact of specific gases on human health rather than the responses or outcomes elicited from the presence of malodorous air in general. Moreover, odor researchers have not been able to demonstrate whether odor triggers a psychological or physiological response. For example, odors have been found to affect cognitive performance, heart rate and electroencephalogram (EEG) patterns (Schiffman, 1995). However, these responses could be the result of a person merely being distraught or angered because of the offensive smell. Conversely, these symptoms could have emerged from a physiological basis, in which olfactory ciliary receptors in the nose bonded to the odorous compounds, eliciting some sort of signal transduction, which was transmitted to the brain via olfactory neurons.

However, if one uses the World Health Organization's definition of health—"A state of complete physical, mental and social well being and not merely an absence of disease or infirmity"óit does not matter whether the odor psychologically or physiologically induces a response. The point remains that an elicited response can occur in the presence of an offensive odor, altering a person's overall state of well being, which is integral to good health.

Effects on Neighbors

Thus far, two scientific studies have been conducted in the United States addressing the effects of industrial swine facilities on the health of nearby neighbors. The first study, "The Effect of Environmental Odors Emanating From Commercial Swine Operations on the Mood of Nearby Residents," was conducted by Susan Schiffman et al. (Department of Psychiatry, Duke University Medical Center). This study used the Profile of Mood States (POMS) to assess the effects of swine odors on mood. Forty-four persons living near large hog operations and 44 controls participated in the study by filling out the POMS questionnaire. The results indicated that people who live near hog operations and experience the odor plumes reported significantly more tension, depression, anger, fatigue and confusion than the control subjects. In addition, the experimental group reported an overall feeling of less vigor (Schiffman, 1995). The mood states of people exposed to malodors is important because mood has been found to play a role in the immune status of an individual, contributing to subsequent disease outcomes (Schiffman, 1995).

The second study, conducted by Kendall Thu, Kelly Donham et al., assessed both the physical and the mental health of residents living near a large-scale swine operation. Physical and mental health information was collected through personal interviews with 18 residents living within a 2-mile radius of a 4,000 sow facility, and 18 demographically comparable rural residents living near minimal animal production facilities. The results indicated that neighbors of large-scale swine facilities reported higher rates of respiratory problems; nausea; headaches; plugged ears; and irritated eyes, nose and throat (symptoms that also have been well-documented among swine-confinement workers) (Thu, 1997). Yet no environmental data was gathered in this study; thus, it is difficult to establish a causal relationship between the swine odors and the adverse physiological health effects. The nearby residents could have been experiencing 'environmental stress syndrome,' a newly coined term for a condition similar to sick building syndrome, where psychological or psychosocial symptoms have triggered a physiological outcome (Donham, 1998). Similar situations eliciting environmental stress syndrome may have occurred at Love Canal in New York and Three-Mile Island in Pennsylvania, where symptoms were reported, yet levels of toxicant that could have contributed to these symptoms were difficult to detect (Donham, 1998).

On the other hand, this study showed no evidence that neighbors of large-scale swine facilities experience higher rates of psychological problems. However, these results could have been due to the relatively small sample size included in the study. Donham hypothesizes that there is a complex interplay between physiological and psychological symptoms, where stressed or over- worked people may feel susceptible and sickly even from hearsay regarding toxicants in the ambient air (Donham, 1998).

Another study entitled, "Viability of Bioaerosols from a Swine Facility," sought to determine concentrations of bioaerosols at different distances from gestation buildings (Homes, 1995). The original intent of this study was to determine the distance at which a nursery building would be safe from pathogenic bioaerosols that could infect newborn piglets. However, the data from the study can also be useful in determining safe distances for neighbors and human activities. Bioaerosol measurements were taken at a 500 sow farrow-to-finish operation in areas located at the intersection of circles and radials (spaced every thirty degrees) surrounding the gestation building. Five circles, ranging from 5 to 300 meters away from the building, were sampled for the following bacterial species: Streptococcus suis, Hemphillus parasuis, Bacillus and E. coli (Homes, 1995). Results of this study confirmed that airborne microorganisms are still viable after traveling considerable distances. For instance, some of the bacteria were detected nearly 200 meters away from the gestation building. However, the day that this study was conducted was "not conducive to bacterial viability because it was very dry and sunny" (Homes, 1995). Therefore, these results may be conservative and cannot be generalized to cloudy, humid days, where higher levels of bioaerosols and greater viability are expected.

Future Research

There are many other avenues of research that merit investigation with regard to the effects of swine odor on the health of swine facility neighbors. For example, during the summer of 1998, Kendall Thu will be initiating a larger study that will examine the levels of hydrogen sulfide, dust and symptomatologies associated with different types of large-scale swine facilities (Thu, 1998). This study also will examine the social relationships between neighbors of large-scale facilities. Moreover, this study will assess whether the clusters of symptoms in neighbors are analogous to the symptoms appearing in swine workers, who spend intense periods of time within swine buildings.

In addition, a study assessing both the ambient air quality of individual residential areas and the symptoms reported by respective residents should be conducted in order to provide insight into whether any correlation exists between these two variables. More investigations are also necessary to accurately determine the dispersion and viability of bioaerosals emitted from swine facilities under a variety of different conditions (Homes, undated). These investigations could be helpful in the development of odor control policies based on separation distances between swine facilities and neighbors. Furthermore, a comparative study between a facility that has implemented odor control technologies and a facility that has not attempted to control odors should be conducted. This type of study could provide insight into what specific technologies are useful in reducing not only swine odors but also the possible health problems triggered by these odors. Moreover, systematic data on different forms of large-scale swine production need to be collected to determine what kind of producers are more likely to be "good neighbors," controlling odorous emissions from their facilities (Thu, 1998). The use of Geographical Information Systems (GIS) in future studies would also shed light on wind flow patterns that transport odors across different landscapes, providing insights into where odor problems are likely or unlikely to exist (Hatfield, 1997).

Effects on Workers

In contrast to the possible effects that swine facility odors may have on neighbors, the effects of these odors on workers have been well studied and documented. Studies describing the adverse respiratory effects on swine production workers have been published in the United States, Sweden, Canada, the Netherlands and Denmark (Reynolds, 1996). Results of these studies concur that approximately 50 percent of these workers experience one or more of the following health outcomes: bronchitis, toxic organic dust syndrome (TODS), hyper-reactive airway disease, chronic mucous membrane irritation, occupational asthma and hydrogen sulfide intoxication (Reynolds, 1996).

In addition, results from a study conducted by the University of Iowa (Reynolds, 1996), which assessed chronic swine worker exposures, indicated a dose-response relationship between increased "doses" of industrial swine environments and decreased Forced Expiratory Volume (FEV1) a measure of overall pulmonary function. Additional studies reveal that this dose-response relationship, indicated by changes in pulmonary function throughout the workday, is a predictor of eventual chronic loss in pulmonary function (Donham, 1998). Another study, conducted by the National Institute for Working Life in Solna, Sweden (Muller-Suur, 1997), confirmed that an acute exposure (3 hours) to airborne swine dust induces intense alveolar inflammation in the lower airways of healthy subjects. This inflammation is due to the recruitment of neutrophils, alveolar macrophages and lymphocytes in the lungs (Muller-Suur, 1997). However, further studies are necessary in order both to determine the specific proinflammatory agents of swine dust and to aid in the development of methods and equipment that reduce worker exposures to these constituents.

2.2.6 Effects of Odor on Local Economies, Property Values, and Community Dynamics

Odors emanating from large-scale swine facilities not only affect human health but also influence local economies, property values and community dynamics. For instance, in North Carolina, travel and tourismóan industry boasting more than nine billion dollars in annual salesóhas suffered immeasurable losses due to national media sources highlighting North Carolina's tainted air quality (Hatfield, 1997). Foul air can also sway consumers away from local businesses, such as grocery stores or other small establishments that are located downwind from a swine facility. Furthermore, the actual swine facilities that are emitting offensive odors also have a direct impact on local economics. Results from a study conducted by Labao reveal that corporate agricultural facilities tend to provoke population declines, lower mean incomes, fewer community services, less retail trade, more unemployment, less participation in democratic processes and "an emerging rigid class structure" (Center for Rural Affairs, 1994). Thus, an increase in corporate hog production in previously uncharted areas, such as western Oklahoma, "can only be expected to accelerate the past trends toward declining rural employment and rural economic decay" (Ikerd, undated).

More specifically, property values also have been adversely affected due to the release of offensive odors from large swine facilities. A study conducted by Abeles-Allison and Conner assessed house sales surrounding eight large hog operations in Michigan. The results revealed "that house values decreased by 43 cents for each additional hog within a 5-mile radius," of the house (Abeles-Allison and Conner, 1990). These results also indicated that the magnitude of adverse effects on property values can vary with respect to both the size of a nearby hog operation and the distance between the facility and a private residence (Palmquist, 1997). Unfortunately, the data for this study were only collected around swine facilities that had received numerous complaints; therefore, the results cannot be generalized. Abeles-Allison and Conner note that it is "reasonable to believe that those farms may have been managed poorly, hence creating a larger nuisance for the surrounding home-owners compared to possible effects on neighbors of well-managed operations" (Abeles-Allison and Conner, 1990). Regardless of these limitations, the results of this study suggest that swine odors have a tangible effect on property values.

An additional study, entitled "Hog Operations, Environmental Effects, and Residential Property Values" (Palmquist et al, 1997) also sought to determine whether swine operations have a significant effect on property values. The scope of the study area included nine counties located in southeastern North Carolina. Results revealed that reductions in the prices of houses within close proximity to swine operations were statistically significant, with prices having a maximum decline of nine percent, depending on the distance and size of the facility (Palmquist, 1990). However, this study did not provide additional data on the particular hog facilities in question. For example, data regarding the specific type of facility, distances between properties and facilities, and wind patterns in the area were not gathered. Thus, future studies investigating these aspects of the odor situation would be helpful in determining a more realistic view of the monetary impacts of swine odor (Palmquist, 1990).

In addition to the adverse impacts on property values, swine odor has woven itself into the social structure of rural communities, creating glitches in existing community dynamics. Swine odor has created social and class demarcations (Thu, 1997), fostering intense conflicts between neighboring landowners. Furthermore, many residents believe that the "construction and presence of the [swine] facility violate core rural values of being a good 'neighbor'" (Thu, 1997).

"Rural 'neighborliness' embodies central cultural principles of egalitarian relationships, reciprocal exchange such as helping…in times of need, mutual respect and being kept informed. The facility's construction and continuing presence [is] viewed as eroding these cornerstones of agrarian life" (Thu, 1997).

Therefore, there are many issuesóother than physiological and psychological healthóthat are embodied in the dilemma associated with swine odor, making it difficult to implement an all-encompassing policy. However, including members of the community in the actual policy-making process may be the best way to prevent the omission of less-evident issues, such as social and interpersonal health. Moreover, a policy concerning swine odor will be more successful if the community is empowered in the decision-making process; instead of having no control over the situation, they will be able to contribute to improving both the air quality in their community and their future overall well-being.

2.3 Gases

2.3.1 Gases of Major Concern

Although severe swine odors can create numerous problems in surrounding communities, the specific gases that either constitute the odor plumes or escape on their own from large-scale swine facilities can also pose serious threats to human, environmental and community health. For example, in Iowa, many incidents of people being "overcome by deadly manure gases" are reported each year (Lorimor, 1994). These incidents include several deaths, among a multitude of minor and severe illnesses. As mentioned above, the four main gases of concern are hydrogen sulfide (H₂S), carbon dioxide (CO₂), ammonia (NH₃) and methane (CH₄). These gases are emitted from the same sources that emit swine odors: swine buildings, waste storage and treatment processes, land application practices and carcass disposal areas. Exposure to elevated levels of these gases, even over a short period of time, can produce symptoms ranging from mild irritation to death in both animals and humans (Taraba and Piercy, undated).

Hydrogen Sulfide (H₂S)

Hydrogen sulfide, produced by both the anaerobic decomposition of protein in swine manure and the bacterial reduction of natural sulfates, is the most toxic gas emanating from swine excreta (Taraba and Piercy, undated). It is heavier than air and soluble in water; thus, it will accumulate in underground pits and other low-lying unventilated areas (Lorimor, 1994). Its distinct odor of rotten eggs can be detected at levels less than 1 part per million (ppm). However, at 100 ppm, hydrogen sulfide deadens the sense of smell and no odor will be detected.

According to the National Institute for Occupational Safety and Health, "hydrogen sulfide is a leading cause of death in the workplace," (NIOSH, 1977 in Thornton, 1996). Moreover, it is accountable for most manure-related deaths in both humans and animals (Lorimor, 1994). The threshold limit value (TLV) or maximum allowable concentration for humans is 10 ppm. Concentrations from 20 - 150 ppm can "severely irritate the eyes after 6 to 8 minutes and the respiratory tract after one hour" (Taraba and Piercy, undated). In addition, levels between 500 ppm and 1,000 ppm induce acute intoxication associated with the following symptoms: sudden fatigue, headaches, anxiety, loss of olfactory senses, nausea, sudden loss of consciousness, optic nerve dysfunction, hypertension, pulmonary edema, coma, seizures and severe respiratory distress, often followed by cardiac arrest and death (Thornton, 1996). Moreover, one to two breaths of 1,000 ppm of hydrogen sulfide causes instantaneous unconsciousness and death through complete respiratory paralysis, unless artificial means of respiration are performed (Taraba and Piercy, undated).

Elevated levels of hydrogen sulfide also can have negative impacts on swine health. Swine living under conditions of 20 ppm can develop fear of light, loss of appetite and nervousness. Concentrations of 50 - 200 ppm can give rise to nausea, vomiting and diarrhea, while levels above 400 ppm can cause death (Taraba and Piercy, undated). (See Appendix A, Table 1, for complete list of the effects of hydrogen sulfide on humans and swine).

Carbon Dioxide (CO₂)

Carbon dioxide, a traditionally non-polluting gas present in the ambient air at a concentration of 350 ppm (0.035 percent) under normal conditions, is a natural respiratory product of both humans and animals. It is also the product of the anaerobic decomposition of organic acids and carbohydrates found in swine manure (C₆H₁₂O₆ Þ 3CH₄ +CO₂) and is generally the most abundant gas generated from manure lagoons during anaerobic decomposition. Carbon dioxide is a colorless, odorless gas that is denser than air and soluble in water (Taraba and Piercy, undated). Although it is prone to disperse within liquid manure due to its density, vigorous agitation often results in the release of significant amounts of carbon dioxide into the ambient air.

At elevated levels, carbon dioxide can cause respiratory problems, eye irritations and headaches. It is not a highly toxic gas; however, it can cause asphyxiation since it dilutes the oxygen content of inspired air. The threshold limit value (TLV) of carbon dioxide is 5,000 (0.5 percent) and acute exposures to air with 100,000 ppm can induce violent gasping and panting (Taraba and Piercy, undated). Average concentrations in swine buildings can range from 1,000 ppm during well-ventilated periods to 10,000 ppm during the winter months when ventilation is minimal. Furthermore, carbon dioxide can act as a narcotic (even when present with adequate amounts of oxygen), and exposure to atmospheric conditions of 250,000 ppm can kill humans and animals within a few hours (Tarabe and Piercy, undated). (See Appendix A, Table 2 for a complete list of the effects of carbon dioxide on both humans and swine).

Ammonia (NH4)

Protein from animal feed is the primary source of swine manure nitrogen, which exists in two predominant forms within manure: ammonia and organic nitrogen (Fulhage, undated). In fresh swine manure, approximately 56 percent of the total nitrogen is present in the form of ammonia (American Society of Agricultural Engineers, 1994). However, the organic nitrogen can be converted to ammonia by bacteria present in the manure; therefore, all nitrogen products expelled by swine can potentially be emitted into the atmosphere through ammonia volatilization (Fulhage, undated). The Environmental Defense Fund (EDF) estimates that over eighty percent of the nitrogen in hog manure is vaporized as ammonia (EDF, 1997). Using this value, the EDF also calculated that ammonia nitrogen emissions--from hog farms in Eastern North Carolina alone--translate to approximately 135 million pounds of nitrogen deposition per year (EDF, 1997).

Ammonia in its pure form is irritating to the eyes at concentrations between 20 and 25 ppm. At levels of 1,500 ppm, exposed persons will cough and froth at the mouth, while at a concentration of 5,000 ppm, the ambient air is deadly (Lorimor, 1994). Fortunately, ammonia has a very sharp, pungent and distinct smell, detectable at levels as low as 5 ppm (Lorimor, 1994). The recommended TLV or maximum acceptable dose is 25 ppm, a level which is debated among safety experts since this concentration can produce burning sensations in the eyes (Lorimor, 1994). (See Appendix A, Table 3, for a complete list of the effects of ammonia on both humans and swine).

Methane (CH₄)

Methane production by swine occurs in both the digestive tract and the manure decomposition process. Gastrointestinal production of methane occurs in varying degrees in all animals; however, it is most prominent in ruminants (Fulhage, undated). Approximately "95 percent of animal methane emissions are from ruminants, and ruminants typically belch 6 to 8 percent of gross dietary energy to the atmosphere in the form of methane" (Van Horn, 1995). The remainder of swine methane emissions predominantly comes from solid manure. In swine, twenty percent of total dietary energy is excreted as volatile solids in urine and feces (Fulhage, undated). All of this energy can potentially be converted to methane in the anaerobic decomposition process that occurs in lagoons (C₆H₁₂O₆ Þ 3CH₄ + 3CO₂) (Van Horn, 1995). The resulting methane is subsequently volatilized into the ambient air. The rate of conversion from manure solids to methane is dependent on a number of environmental factors including temperature, pH, humidity and the presence of bacterial nutrients (factors that should be considered in any manure management program).

Once methane is emitted into the atmosphere it is highly combustible, making it very dangerous, especially in high temperature conditions. At levels of 50,000 ppm (5.0 percent of ambient air), methane can spontaneously explode (Lorimor, 1994). Methane is also dangerous because it is colorless, odorless, and tasteless, making it very difficult to detect. The TLV for methane is 1,000 ppm (1.0 percent of ambient air) and, since methane is lighter than air, it can potentially reach this concentration at the top of unventilated areas such as closed manure pits (Lorimor, 1994). However, manure pits are not known to emit significant levels of methane. (See Appendix A, Table 4, for a complete list of the effects of methane on both humans and swine).

2.3.2 Measuring Swine Gases

Measuring swine gases is a relatively straight-forward procedure, unlike the complex and problematic processes involved in measuring swine odors. A hydrogen sulfide analyzer is utilized to measure concentrations of hydrogen sulfide, while an infra-red analyzer can be used to measure both carbon dioxide and methane. A chemiluminescent NO_x analyzer is often used to analyze the levels of ammonia in ambient air; although traditional methods, such as gas chromatography and mass spectrometry, are also utilized (Sweeten, undated).

Unfortunately, since most of the research concerning swine facility airborne emissions has focused on the odor issue, there have been few studies that provide any information on the levels of gases present in communities surrounding large-scale swine facilities. However, one study, concerning the measurement of hydrogen sulfide emitted from swine facilities, has revealed useful results.

In the summer of 1994, in Renville County, Minnesota, there was concern among some residents that two manure holding ponds of a nearby hog operation were emitting dangerous levels of hydrogen sulfide, which induced fits of vomiting, nausea and blackout periods in both adults and children (DeVore, 1997). In response to this concern, the Minnesota Department of Health (MDH), along with the help of local citizens, conducted a study testing for airborne hydrogen sulfide at a number of different sites, including beef, dairy, poultry and swine operations, and a beet processing plant (MDH and MPCA, 1996). Continuous monitoring, with the use of a Jerome Hydrogen Sulfide Analyzer, was performed over half-hour or full-hour monitoring periods (MDH, MPCA, 1996). Results indicated that the beet processing plant and the swine operations had the highest hydrogen sulfide emissions. Average swine emissions ranged from 0 to 47 parts per billion (ppb) during 30-minute sampling periods. However, hydrogen sulfide levels from 8 to 53 ppb were recorded near six swine operations. These tests laid the groundwork for the Minnesota Feedlot Hydrogen Sulfide Program discussed later in Section 4.1.7.

The results were helpful in revealing 'above normal' levels of hydrogen sulfide around swine operations. Yet, since emissions from these operations are unpredictable and uncontrolled, it is difficult to generalize these results to facilities that were not involved in the study. Thus, the MDH recommended that Renville County residents, who are concerned about hydrogen sulfide levels, should be provided with portable monitors, so that MDH can "better characterize the nature of emissions and enable the county to respond to complaints" (MDH and MPCA, 1996). Perhaps this method of "case-by-case" measuring of hydrogen sulfide is the best way for individual counties to control these emissions until a national ambient air quality standard (NAAQS) for hydrogen sulfide is established. However, future investigations concerning the swine emissions of hydrogen sulfide and other dangerous gases, such as ammonia, carbon dioxide and methane, should also be conducted. The results of these studies could enable standards for each of these gases to be developed if it is found that the gases reach levels that compromise public health.

2.3.3 Effects of Swine Gases on the Environment

Although it is important to measure gaseous swine emissions for the purposes of protecting public health, it is also important to measure these concentrations in order to determine whether swine gases are contributing to adverse effects on the environment. Recently, there has been concern that the abundance of ammonia emissions from swine facilities is contributing to the over-fertilization of nitrogen-sensitive prairies, "resulting in the proliferation of weedy species at the expense of native plants…" (Rudek, 1997). In addition, since the Midwest is a drainage basin for the Mississippi River system, it is thought that the excessive amounts of nitrogen deposition (by route of ammonia emissions) being delivered to the Gulf of Mexicoóvia the Mississippi Riveróare contributing to the recently discovered "dead zone" (Rudek, 1997). This phenomenon of nitrogen deposition in the hydrosphere (the waters of the earth) is believed to have taken place in North Carolina, where 135 million pounds of nitrogen emitted from swine facilities has potentially contributed to the decline in estuary health along the North Carolina coast. However, the scientific community is not in complete agreement concerning this issue because there is limited long-term data on atmospheric levels of swine ammonia (Fulhage, undated).

In addition to the potential environmental problems caused by ammonia emissions, methane and carbon dioxide emissions from large-scale swine facilities may be contributing to even greater environmental problems. Methane, a gas that has been implicated in the degradation of the earth's ozone layer, is also a greenhouse gas, capable of absorbing enormous amounts of radiation. Carbon dioxide is a greenhouse gas as well, although it is not nearly as damaging as methane, which "on an equal weight basis [absorbs] 70 times as much infrared radiation as carbon dioxide" (Fulhage, undated). This absorption of infrared radiation has been implicated in the controversial debate concerning the existence of global warming; thus, if it is proven that global warming truly is a reality, then the gaseous emissions of industrial swine facilities are also contributing to the warming of the planet.

2.3.4 Summation

Whether or not it is proven that swine odors and gases contribute to public health and environmental problems, the presence of these emissions still has a negative overall effect on the quality of life of workers and neighbors of large-scale swine operations. People have been psychologically affected, property values have been depressed, local economies are suffering and community dynamics have been interrupted and altered, to say the very least. Thus, if large-scale swine facilities intend to remain next-door-neighbors to rural America, it is imperative that the levels of odor and gas emissions be either reduced or controlled in both the indoor and outdoor environments of these facilities. The following section of this paper will introduce methods by which this effort can be successfully achieved.

• Part 3 - Methods of Odor Control

• Table of Contents

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