Air Quality Issues
Relevant Federal and State Legislation
The federal Clean Air Act Amendment of 1990 (CAAA) has provisions of importance to producers of agricultural products. Although protecting air quality has inherent implications for livestock and poultry health as well as profitability, the language of air quality is derived principally from environmental regulations designed to protect public health and the use and enjoyment of private property. Public health concerns relating to gases and aerosols (and, to some extent, their associated odors) are expressed in ambient air quality standards, emissions permits and nuisance legislation.
Understanding Air Quality Issues
The handling and storage of manure associated with confinement livestock and poultry systems generates a wide range of air-borne contaminants including ammonia, carbon dioxide, hydrogen sulfide, and methane. These contaminants are dispersed in gases, aerosols, and dusts. The occurrence and concentration of individual contaminants vary substantially with animal species and type of confinement facility. In addition to chemical contaminants, potentially allergenic and pathogenic microbes can be dispersed in aerosols and dusts associated with manure handling and storage. Air-borne contaminants can have direct and indirect effects on human health, the environment, and the social impacts of communities.
Impact on health and communities
Odor nuisance to neighbors of livestock and poultry operations is a common source of discontent within communities and these concerns should be taken seriously. It is often the cause of opposition to new or expanding facilities, as well as heightened scrutiny of other environmental issues. Recent research suggests that neighbors have strong emotional reactions to livestock-related odors. These reactions can impact psychological and physiological health resulting in significantly greater anger, confusion, tension, depression, and fatigue in populations living near intensive livestock operations.
Physiological responses to odorous compounds are not well understood but appear to be limited in nature. Reports suggest that odors may elicit respiratory problems with nausea, vomiting, and headaches. Although some compounds associated with odor (hydrogen sulfide and ammonia) are toxic in high concentrations, neighbors of livestock operations are rarely exposed to toxic levels. It is unclear if long-term, low-level exposure to compounds can impact the health of neighboring residents. A consensus among health professionals does not exist at this time.
Source of contaminants
Over 160 volatile compounds are found in gaseous emissions from confinement facilities. Many of these volatile compounds contribute to odors and raise concerns about human health, while others, including methane and carbon dioxide, may contribute to global warming. Some community concerns and regulatory efforts have focused on individual gases while others have focused on the general issue of odor.
Metabolic processes within the gastrointestinal track of livestock and anaerobic degradation of manure generate most of these compounds. Anaerobic degradation involves the reduction of complex organic compounds to a variety of odorous volatile fatty acids (VFAs) by acid-forming bacteria. Methane-forming bacteria convert VFAs to methane and carbon dioxide, which are odorless. When in balance, these anaerobic processes eliminate odorous compounds. However, in manure storage or overloaded anaerobic treatment lagoons, acid-forming and methane-forming processes are not in balance, resulting in an accumulation of VFAs.
Sulfate-reducing bacteria found in anaerobic environments convert sulfate to hydrogen sulfide and other sulfur-containing compounds that contribute to odor. Hydrogen sulfide has a strong odor like rotten eggs at low concentration levels; but it has a sweetish odor when more concentrated. Odor, though, should not be used as a warning of exposure; since at concentrations of 20-30 ppm hydrogen sulfide may weaken the sense of smell. Public health concern may arise since exposure to concentrations of 2,000 ppm for a few minutes can be fatal. Long-term exposures at 300 ppm have also caused deaths. Such high concentrations of hydrogen sulfide are more likely to collect in confined spaces such as manure pits. Ambient air regulations in Nebraska specify that hydrogen sulfide concentrations cannot exceed 50 ppm (30-minute average), or 20 ppm (1-minute average). Research at the University of Nebraska-Lincoln suggests that hydrogen sulfide emissions from feedlots are unlikely to exceed regulatory limits.
Ammonia is released in large quantities by livestock production systems. Anaerobic lagoons may lose more than two-thirds of the nitrogen in manure as ammonia. Open lots for livestock production will volatilize roughly half of the nitrogen, primarily as ammonia. The main problem associated with ammonia relates to its deposition on land and water and its chemical combination with other aerial compounds to produce particulate matter that causes haze and may contribute to health concerns.
Odorous volatile compounds are commonly considered to be a nuisance by many neighbors of confinement facilities. A neighbor’s determination of odor nuisance is related to physical factors (frequency, intensity, and duration of odor experience) and social factors (past experience with agriculture, relationship with the producer, and appearance of the livestock or poultry operation). Odor is defined in terms of four factors (FIDO factors): Frequency – how often does the odor occur? Intensity – how strong is the odor? Duration – how long does the odor persist? Offensiveness – to what extent does the odor offend individuals exposed to it?
The four FIDO factors are not independent; they interact in predictable ways. For example, although the actual intensity of two different odors may be equal, the offensiveness of one odor may increase the ability of a person to sense it, while that same person may be relatively insensitive to the other less offensive odor. The most commonly cited odor parameter is intensity, defined as the number of volume dilutions (volumes of odor-free air added to a unit volume of odorous air) required to reduce the odor to a level that is barely detectable by 50 percent of a group of human panelists exposed to the odor under controlled conditions.
Sources of odor
For new facilities, odor management is first and foremost an issue of site selection. Choosing locations that take into account prevailing winds and neighbors is important. In established livestock operations, proper manure handling, moisture management, and dust control can eliminate many odor complaints.
Lagoons are typically designed for the anaerobic digestion process. An anaerobic lagoon is a structure that is designed to treat and store manure. A properly designed and operated anaerobic lagoon should not produce the odors that a manure storage facility often emits. Manure storage structures are often mistaken for lagoons. A manure storage facility is a structure designed to store manure and effluent generated from a livestock operation.
In addition to odorous compounds, dust emissions from animal confinement facilities are gaining greater attention due to their ability to serve as a carrier of odorous compounds and microbes with the potential to impact the health of facility workers and neighbors.
Fungi are naturally found in livestock and poultry operations and are a legitimate concern. Several species infect and cause disease in humans ranging from dermatitis to invasive diseases of the lung that are sometimes fatal. In addition, some fungi produce toxic compounds called mycotoxins that can produce pneumonia or disrupt the function of target organs such as the kidney,liver, and spleen. As with bacteria, the exposure risk is much higher within the production facility and decreases at distances from the facility. Unlike bacteria, treatment for fungal infections is more difficult. Although predisposition is not required for infection to occur, modern medical practices, such as treatment with antibiotics, corticosteroids, and immunosuppressive drugs predispose humans to infection by fungi.
How Do Contaminants Get Into the Air?
|Common pathways for manure contaminants to pollute the air.|
Airborne emissions from animal production systems originate from three primary sources: manure storage and treatment facilities, animal housings, and land application activities (Figure at right). The movement or dispersion of airborne emissions from animal feeding operations (AFOs) are affected by topography, prevailing winds, and orientation. Generally, plumes from odorous sources are more intense under stable atmospheric conditions. This means on calm, cool days the odor plume will be very intense just downwind of the source. Conversely, unstable conditions, such as a warm day or windy conditions, tend to disperse and dilute air emissions.
Issues of Local Concern
The previous discussion introduced many potentially negative impacts of manure on the environment. Within your local community, it is likely that only a few of these potential issues are of critical concern. These high-priority issues may result from unique local conditions, a history of environmental concerns, or from public policy and regulatory actions.
It is important that the producer’s future investments of time and resources focus primarily on high-priority local environmental issues. These priorities should be considered in your livestock operation’s future environmental stewardship efforts.