The magnitude of the problem is probably quite large. Donham and Gustafson (1982) estimated that 700,000 persons in the United States are occupationally exposed to confinement livestock and poultry housing. A survey of 2459 Iowa livestock confinement workers showed that over 60 percent of those responding reported some type of adverse effect including cough, sore throat, runny nose, eye irritation, headaches, tightness of chest, and muscle aches and pains (Donham and Gustafson, 1982). The Federal Register(1992) stated that "..the illness incidence rate among agricultural workers for 1989, the latest year reported by the Bureau of Labor Statistics, was 45.5 per 10,000 full-time workers, higher than mining and construction." It continues, "In addition, these statistics are believed to underestimate agricultural morbidity by a large margin because OSHA does not require recordkeeping and reporting by farms with 10 or fewer employees and because workers' compensation laws in most states do not cover farms with few employees."

The objective of this paper is to give an overview of the human health hazards associated with confinement livestock and poultry facilities.

DEFINING THE ENVIRONMENT

The environment within livestock and poultry buildings contains many different potential hazards to the worker. These include gaseous contaminants, such as ammonia and hydrogen sulfide, particulate contaminants (dust), excessive noise, substandard lighting, and physical hazards associated with animal interaction. While many hazards are obvious, the gaseous and particulate contaminants can be subtle and may slowly affect the agricultural worker.

Gaseous Contaminants

Dry outdoor air is approximately 78.09% nitrogen, 20.95% oxygen, 0.93% argon and 0.03% carbon dioxide, with slight traces of inert gases. Due to breakdown of animal manure, respiration of animals, and use of unvented heaters within the buildings, the environment develops into one that may be harmful to animals as well as agricultural workers. The physiology of animals, as well as waste handling systems and other housing characteristics make different gases critical depending on the animal type. Table 1 illustrates which gases may be associated with different types of animal housing. Gas sources and the relative effects on humans are summarized in the following sections.

Table 1. Relevant Gases in Different Housing Systemsa.

Gas NH3 CO CO2 H2S CH4 Poultry Yes Yes Yes Swine Yes Yes Yes Veal Yes Yes Yes Sheep Yes Yes Yes Cattle Yes Yes Yes only in buildings with liquid manure systems only in buildings with liquid manure systems

a. adapted from Mutel et al, (1986)

Ammonia: Ammonia is a pungent toxic gas that is detectable with the human nose even at low concentrations. It is released from fresh and decomposing manure, particularly in situations in which manure has a chance to dry. High temperatures promote its production, (DeBoer and Morrison, 1988). Ammonia is an irritant that inflames wet body tissues, such as the eyes and lungs, even at low concentrations. The physiological response of humans to ammonia begins with detectable odors at 5 to 50 ppm (DeBoer and Morrison, 1988). Irritation to mucous surfaces occurs at 100 to 500 ppm. Immediate irritation of eyes, nose and throat occurs at 400 to 700 ppm. Severe eye irritation, coughing and frothing at the mouth, which could be fatal, occur at 2000 to 3000 ppm. Respiratory spasm and rapid asphyxia may occur at 5000 ppm. It is rapidly fatal at 10,000 ppm.

Hydrogen Sulfide: Hydrogen sulfide is a toxic gas that is heavier than air. At low levels, it has a characteristic odor similar to rotten eggs. It is produced during anaerobic decomposition of manure and is therefore associated with deep pits. Dangerous levels of the gas may be present during agitation and pumping of deep manure pits. Twenty-four deaths related to hydrogen sulfide exposure occurred in the Midwest between 1984 and 1991 (Donham,1991a). One possible reason that fatalities occur so often is that olfactory senses are paralyzed at high concentrations and so victims can not detect odors.

Hydrogen sulfide is classified as an irritant at sub-lethal levels. According to DeBoer and Morrison(1988), the least detectable odor occurs at 0.01 to 0.7 ppm. An offensive odor is detectable at 3 to 5 ppm with eye irritation at 10 ppm. Irritation to mucous membranes and lungs occurs at 20 ppm. Olfactory-nerve paralysis occurs at 150 ppm, followed by headaches, dizziness and nervous system depression at 200 ppm. Nausea, excitement, insomnia and death may occur after 30 minutes of exposure at 500 to 600 ppm. It is rapidly fatal at 700 to 2000 ppm.

Carbon Dioxide:Carbon dioxide in the normal atmosphere is approximately 300 ppm on a volummetric basis. It is produced primarily from respiration of animals with lesser amounts coming from decomposition of manure. Unvented heaters also add carbon dioxide to the interior atmosphere.

Carbon Dioxide can be classified as an asphyxiant in high enough concentrations. Levels of 20,000 ppm are safe with increased breathing rate occurring at 30,000 ppm. This is followed by drowsiness and headaches at 40,000 ppm and heavy breathing at 60,000 ppm. Violent panting occurs at 100,000 ppm. Potential fatality may occur after a few hours of exposure to 250,000 ppm or 30 minutes at 300,000 ppm.

Carbon Monoxide:Carbon monoxide could be a problem in situations where incomplete combustion is occurring in unvented propane or natural gas heaters, or from an internal combustion engine. During winter operation when buildings are using heaters and maintained with minimum ventilation this should be of special concern. The toxicity is caused by rapid absorption of carbon monoxide in blood and replacement of oxygen on hemoglobin cells. Because of this replacement, it takes time for recovery and repeated exposures of low concentrations may be harmful. Carson (1990) stated that sow exposure to carbon monoxide concentrations greater than 200 ppm may cause stillbirths.

Methane:Methane is an explosive gas. It is produced during anaerobic decomposition of manure and is highly flammable in concentrations above 5 to 15% by volume in air.

Measurement of Gases:DeBoer and Morrison (1988) quoted Donham as stating that there are several reasons why gas measurement might be useful. These include: 1) to assure good air quality during everyday operating procedures; 2) to document possibly harmful levels where human or animal health problems have been noted; 3)to assure that toxic gas levels are not rapidly rising when undertaking potentially dangerous tasks (e.g., agitation of liquid manure); 4) to investigate premises where losses of hogs due to building or ventilation malfunction may lead to suits against maufacturerers; and 5) to evaluate the effectiveness of building management procedures or retrofitted environmental control systems.

There are several types of gas measuring devices available. The most common for field measurement are detector or colorimetric tubes that are used with a hand-drawn air pump. The detector tubes (which cost approximately $4 each) are made of glass and are made gas specific. Sampling is done by breaking the ends of the glass tube and using the air sample pump to draw a sample through the tube. The medium within the tube will change colors and can then be read to indicate the level of gas concentration. Gas sample pumps are priced between $200 and $350 dollars. The detector tube method is an instantaneous reading method.

Dosimeter tubes may be used to develop an exposure history of a worker to a certain gas. They look like the detector tubes except are used as a passive measurement over some period. They are worn on the lapel of a worker. The medium within the tube changes color to indicate the level of gas exposure. The reading is then divided by the number of hours of exposure to find the average worker exposure. The main disadvantage to the dosimeter tubes is that they are slow to react and are not a good warning system for lethal gas exposure. Dosimeter tubes are approximately $4 each.

Solid state electronic detectors are also available that are capable of continuously monitoring the environment. Many have an audible alarm built into the system. They are quite expensive with most costing more than $1000.

Particulate Contaminants

Particulate contaminants, or more commonly dusts, are not only a nuisance, but also can contribute to worker and animal health problems. According to Donham (1986), dusts may be composed of dried fecal material, feed, animal dander, feathers, mold, pollen, grain mites, mineral ash, gram-negative bacteria, endotoxin, microbial proteases, ammonia adsorbed particles and infectious agents. Feddes et al.(1992) stated that in turkey housing studies, airborne respirable particles were primarily fecal material.

Particles are classified according to size. Particles larger than 10 mm usually settle out of the air rapidly (DeBoer and Morrison, 1988). If they are inhaled, they are trapped by moist tissue in the nose and throat. They may cause irritation of the nose and throat and cause sneezing. Particles 5 to 10 mm in size will reach the windpipe causing irritation of the lining and possible infection. Particles less than 5 mm, called respirable particles, may reach the bronchioles and alveoli, and therefore present the most hazard.

Dusts adversely effect health by directly irritating tissue and by causing allergic reactions in response to inhaled foreign particles. It also transports embedded microorganisms and adsorbed gases deep into the sensitive tissue of the lungs. Endotoxin is of particular concern to agricultural workers. It is a substance found in the cell wall of Gram-negative bacteria and has a high biological potency. It has been linked with respiratory symptoms in workers.

Measurement of Particulates: Dust can be sampled in many ways. One of the most common is to use a small air sample pump to draw air through a filter at the rate of 1.7 to 1.9 l/min. The filter is then weighed and the sample weight is divided by the total flow (rate times time) to get the particulate concentration in g/l. To measure only the respirable fraction, a cyclone is used to separate out large particles before they get to the filter. Other methods of dust collection include thermal precipitation, sedimentation, impaction, optical counters and electrostatic precipitation.

Bioaerosol measurement is more difficult. Bacteria and molds are generally collected using impaction samplers into solid culture medium. Medium is then cultured and colony forming units (cfu) are counted. Viruses are generally collected in liquid medium and inoculated into tissue cultures. Endotoxin analysis has been performed by taking dust samples and assaying them by using Limulus amoebocyte lysate (LAL) assay. Commercial test kits are then used for checking the assay (Feddes et al.,1992). Endotoxin is believed to reside predominantly in the respirable fraction (DeBoer and Morrison, 1988).

HEALTH IMPLICATIONS

Worker health implications in swine housing has received a great deal of attention in the past. Donham, et al.(1984) surveyed swine confinement producers and non-confinement workers for chronic respiratory disease symptoms. The comparison of the two groups is shown in Table 2. They concluded that confinement workers experienced significantly higher prevalence of chronic bronchitis and wheezing (odds ratio 7 and 4, respectively). Whyte, et al (1993) stated that 10% of United Kingdom poultry stockmen had respiratory impairment and that layer stockmen were exposed to more hazardous environments due to the practice of "blowing out" cages with compressed air. Twenty percent of the farms in their study exceeded the standard for dust exposure in the UK by 2.5 times.

Table 2. Chronic Respiratory Disease Symptoms (Donham, et al., 1984)

Symptoms Confinement Swine Producers N=24 Nonconfinem ent Swine Producers N=24 Chronic Cough 33% 8.3% Chronic Phlegm 58% 21.0% Chronic Episodic cough with phlegm 29.2% 4.2% Chronic Wheezing occasionally apart from a cold 62.5% 29.2% Chronic Wheezing most days or nights 4.2% 4.2% Shortness of Breath 20.8% 20.8% Frequent Chest Colds 45.8% 20.8% Off Work with Chest Illness 8.3% 0

Donham (1991b) listed 10 conditions that swine producers experience as a result of exposure to harsh environments in confinement buildings. They are listed below:

Hydrogen sulfide poisoning: This occurs only in facilities that have liquid manure storage and is of great concern during liquid manure agitation. Levels of 400 ppm will cause poisoning.

Bronchitis: Cough and coughing up phlegm are most common complaints. It is considered chronic if it occurs for 3 or more months per year for 3 years. Twenty to 60% of swine producers have this condition with an additional 30% having an acute case. Long term irritation causes deterioration of the airway linings. Cells produce extra mucous and cilia do not work properly, therefore particulate removal is less effective. Particles can only be removed by coughing up phlegm.

Hyperactive airways disease:Tightness of chest and wheezing are the main symptoms. Muscle cells in the airway become inflamed and enlarged, and will constrict upon almost any irritation thereby causing the airways to become narrower. This condition is seen in 20 to 30% of the swine producers.

Atopic asthma: Wheezing caused by an allergic reaction occurs within a few minutes of exposure. Less than 5 % of swine farmers experience this.

Acute organic dust toxic syndrome: Symptoms include fever and flu-like illness with headaches, muscle pains and chest tightness. Thirty to 40% have had episodes. This is attributed to some activity that exposes the producer to dust, (such as moving hogs or catching chickens) and it begins 2 to 6 hours after exposure. Endotoxin exposure is felt to be the toxicant.

Chronic organic dust syndrome: Symptoms include chronic tiredness, muscle aches and pains, and chronic shortness of breath. With proper protection they get better. Symptoms are related to long term lower exposures to the confinement environment. Endotoxins are a suspected cause.

Mucous membrane irritation: Symptoms include sore throat, irritation of the eyes, nose and sinuses. Thirty to 50% of swine producers experience this.

Increased susceptibility to other chest illnesses:Symptoms include frequent colds and pneumonia. Twenty to 30% report this condition.

Chronic sinusitis: Dizziness, chronic cold, and ears popping are prime symptoms. Twenty to 40% of swine producers experience this.

Byssinosis-like condition:The person experiences increased symptoms of cough and chest tightness after several days away from the confinement house.

In addition Mutel et al.(1986) reported that respiratory infectious diseases are another potential hazard. These include Newcastle disease in poultry confinement, Q fever from situations which call for assisted animal births and swine influenza. In addition, DeBoer and Morrison (1988) name tuberculosis, anthrax, brucellosis, leptospirosis, salmonella, streptococcus, staphylococcus and viral or fungal infections as other possible hazards.

REGULATIONS

In 1992, the Federal Register(1992) detailed a proposal to set permissible exposure limits for agricultural workers. Farming operations that do not maintain a temporary labor camp and that employ 10 or fewer employees were exempt from OSHA regulations. The proposal did however state that "Swine and poultry confinement buildings are sources of especially high exposures". The new section for agriculture of 29 CFR was to be numbered 1928.1000 and included approximately 220 substances that had unestablished exposure limits previously.

Regulations are generally set at a level at which few workers will show adverse effects with repeated exposure. Federal Register (1992) defined the following terms that are used to quantify the environment of the worker.

Time Weighted Average (TWA): is the employee's average airborne exposure in any 8 hour work shift of a 40 hour work week. Concentrations are set to which nearly all workers may be repeatedly exposed without adverse effects.

Short Term Exposure Limit (STEL): is the employee's 15-minute timeweighted average exposure which shall not be exceeded at any time during a work day. DeBoer and Morrison(1988)state that these are set at concentrations to which workers can be exposed continuously for a short period of time without suffering from irritation, chronic or irreversible tissue damage, or narcosis which may increase the likelihood of accidental injury, impair self-rescue, or materially reduce work efficiency.

Ceiling:is the employee's exposure which shall not be exceeded during any part of the work day. If instantaneous monitoring is not feasible, the ceiling shall be assessed as a 15-minute time weighted average exposure which shall not be exceeded at any time over a working day. This concentration level should not be exceeded even instantaneously due to fast acting physical impairments that may occur.

Table 3 contains the proposed values for agriculture contained in 29 CFR 1928.1000. Values for other occupations from the American Conference of Governmental Industrial Hygienists (ACGIH) are shown for comparison.

Another important aspect of the proposed regulation was the way in which

exposure to multiple substances were handled. A worker's measured TWA values for each substance was divided by the permissible exposure limit for that substance. This is done for each substance to which a worker is exposed . These numbers are then summed and must be less than one in order to comply with the regulations.

Currently, 29 CFR 1928.1000 has not been adopted and appears to be vacated due to lawsuits contesting the process of establishing levels. However, it is important to note that they were proposed and because other working environments must adhere to similar standards, agriculture is vulnerable. If workers are adversely affected by exposure within confinement facilities and choose to take legal action against an employer, the lack of a standard will not prevent them from prevailing. This is an issue on farms of all sizes. It is a high probability that at least certain substances will be reproposed. There is also a probability that the 10 employee exclusion rider will be amended.

Table 3. Pertinent Permissible Exposure Limits in ppm

Substance Ammonia Carbon Dioxide Carbon Monoxide Hydrogen Sulfide Particulates (mg/m3) Total Dust Respirable Proposeda TWA - 10,000 35 10 15 5 STEL 35 30,000 - 15 - - Ceiling - - 200 - - - ACGIHb TWA 25 5000 50 10 10 - STEL 35 30,000