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I. AGRICULTURAL DUSTS AND GASES Perhaps more than any other occupational group, agricultural workers are exposed to a tremendous variety of agents potentially harmful to the respiratory system. Regardless of the type of agricultural operation, workers are likely to inhale some of these substances on a daily basis: particles of hair, feathers, dander, gut epithelium, or feces; pollen grains; bacteria, their spores, and endotoxins; fungi, their spores, and mycotoxins; chemical residues; infectious disease agents; antibiotics, growth promoters, or mineral supplements fed to animals; fumigants; the gases hydrogen sulfide (H2S), oxides of nitrogen (NOx), or ammonia (NH3); and fumes arising from diesel engines or welding. These substances originate from the soil, the animals and plants raised on farms, animal wastes and their breakdown products, animal feeds, products of decay or fermentation of stored plant materials, insects or mammals infesting stored plant materials or farm structures, applied pesticides and fertilizers, their residues, and operation of farm machinery. Even with extreme care, it would be impossible to avoid regularly inhaling many of these substances on a typical farm. Farmers are commonly exposed to low concentrations when performing numerous daily chores. High concentrations of certain harmful dusts or gases are typical of many agricultural activities: moving or transporting grain, uncapping silos, breaking open bales of spoiled hay, mixing feed or feeding animals, cleaning moldy grain out of storage structures, entering recently filled nonairtight silos, working in a livestock confinement unit or near its associated manure storage area, applying pesticides or anhydrous ammonia fertilizer, and working with diseased animals. Exposure to any substance is likely to be more intense, and its effects more damaging, if it occurs within an enclosed structure. Such exposures are most typical of winter months. Since some of these activities are performed by agricultural workers other than farmers or ranchers, exposure hazards extend well beyond the farm or ranch to a variety of related occupational groups: grain elevator workers, animal slaughterhouse workers, truckers, professional pesticide applicators, and veterinarians. Exposure of farm family members (including children) who help part-time with farm operations also can be significant. Respiratory responses to inhalation of these substances are governed by characteristics of the dusts and gases. The great majority of agricultural dusts are organic particles. Unlike inorganic particles such as rock particles in soil, which may produce a nuisance effect, organic particles are often biologically active, capable of producing irritating, allergic, toxic, inflammatory, or infectious responses. Responses may be acute or chronic, resolving completely or resulting in permanent impairment and disability, and sometimes ending in death. Agricultural dusts commonly range in diameter from under 1 micron to over 50 microns and thus may be deposited throughout the airways and alveoli and induce a response in any part of the respiratory tract. Various types of dust particles form an endless variety of mixtures. Unlike an industrial setting where a few known dust components produce a specific identifiable respiratory response, components of farm dusts are never completely identified. These components vary with each season, type of farming operation, and type of chore being performed. Gases or pesticide residues may adsorb to dust particles, further complicating the picture. Thus an individual may be experiencing more than one respiratory response, which may be synergistic and cumulative. II. RESPIRATORY RESPONSES TO INHALED AGRICULTURAL SUBSTANCES An individual's respiratory response to this complex mixture of dusts and gases will depend on many factors: composition, irritative and antigenic properties of inhaled substances, size and shape of dust particles, location of deposition in the respiratory tract, intensity and duration of exposure, and the individual's susceptibility including immunologic status. Two other important factors are the individual's smoking history and occupational or environmental exposure to nonfarm respiratory hazards. Many respiratory effects described in this series are significantly worse among smokers. And, with the troubled farm economy, farmers are increasingly likely to hold a nonfarm job that may pose its own risks to the respiratory system. For all of these reasons, respiratory responses to dusts and gases in agricultural settings are complex. Except in rare instances, neither the exposure nor the resulting response is clear-cut. Nevertheless, because the respiratory tract has a limited number of recognized responses, specific agriculturally-related respiratory diseases have been recognized for many years. Respiratory responses to agricultural dusts and gases are listed in Table 1, and described in the following paragraphs. Specific exposure circumstances and resulting disease entities are outlined in Units 1-7 of this series. Details of diagnosis and treatment of these conditions are also explained in these seven units. Table 1 Agricultural Respiratory Responses
Bronchitis is the most common agricultural respiratory problem. Cough and sputum (with or without airflow obstruction) typically are noted in 20 to 90% of a farming population, depending on the type of farm and associated exposures. Cough and sputum lasting over two years (chronic bronchitis) are noted in as many as 50% of swine confinement workers and grain handlers. These conditions occur nearly twice as commonly as among blue collar comparison populations, even though agricultural workers are known to smoke significantly less than other blue collar workers. Other symptoms and conditions that commonly accompany agriculturally induced bronchitis include rhinitis, pharyngitis, laryngitis, asthma, and hyperresponsive airways. Obstruction of airflow may be associated with bronchitis, and among some groups of agricultural workers, such as grain handlers, occupational exposure appears to be linked to chronic obstructive pulmonary disease. Exposure to irritants, usually organic dusts, is probably the most common cause of bronchitis. Irritant gases such as H2S and NH3 may also be involved, but these usually are found in combination with organic dusts. Extrinsic asthma and allergic rhinitis, like bronchitis, are caused by exposure to organic dusts. However, asthma is not nearly as common as bronchitis. Because organic dusts are a complex mixture of potential allergens, it is difficult to determine the specific causal agent. Grain mite exposure appears to be one important cause. Although exposure to aeroallergens may be much more intense in the agricultural setting, it is not clear whether asthma is more prevalent in rural areas than in urban settings. Hypersensitivity pneumonitis is a granulomatous response of the lung parenchyma arising from repeated inhalation of certain organic dusts. In the case of farmer's lung, the common name for hypersensitivity pneumonitis seen in the agricultural setting, the primary antigenic agents are spores of several species of thermophilic actinomycetes and certain fungi. Although cases of the toxic organic dust syndrome (TODS) present similarly to those of acute farmer's lung, TODS is an inflammatory rather than allergic response of the alveoli. This response may be triggered by grain dusts, dust in confinement livestock buildings, and dust from mold and bacterial-laden plant materials. Ammonia, H2S, and NOx are irritant gases frequently encountered in the agricultural environment. When inhaled, these gases may induce inflammation of the entire respiratory tract, associated with cough, chest pain, dyspnea, and occasionally hemoptysis and pulmonary edema when gas levels are high. Severe acute airway inflammation with edema could occur from exposure to H2S during manure pit agitation, from exposure to NOX in newly filled silos, or from exposure to NH3 when anhydrous ammonia fertilizer escapes in an enclosed space. At very high concentrations, these gases may induce immediate respiratory distress, with sudden collapse and death. Later sequelae among those who survive such exposures may include bronchiolitis or bronchiolitis obliterans. Ingestion of the herbicide paraquat causes a latent progressive proliferation of pneumocytes and fibrosis in the lung parenchyma almost always with a fatal outcome. The mechanism of this unusual toxic reaction is poorly understood. Symptoms and signs of infectious pneumonitis are like those of other generalized febrile illnesses, accompanied by signs and symptoms typical of pneumonia. The specific course of the clinical presentation depends on the specific infectious agent. Histoplasmosis, ornithosis, Q fever, bovine TB, hydatidosis, Newcastle disease, swine influenza, and tularemia are infections with major respiratory involvement that are associated with the agricultural environment. III. MEDICAL SURVEILLANCE OF THE AGRICULTURAL WORK FORCE Because respiratory illness is a major problem of agricultural workers, farm workers need to be evaluated both for acute conditions resulting from occupational exposures and for development of chronic pulmonary disease. Health care professionals need to be aware of the variety of agricultural processes resulting in occupational exposures and respiratory conditions. Too frequently, respiratory illnesses among farmers are diagnosed incorrectly, and farmers return to a work setting that further induces or aggravates the illnesss. Awareness coupled with routine attempts to trace respiratory illness back to a possible occupational source will help reduce misdiagnosis, and will encourage use of preventive measures specific to the problem at hand. All agricultural workers should have a periodic thorough physical examination including a detailed occupational and clinical history. The occupational history should establish characteristics of the work environment and common activities that could lead to respiratory illness. Smoking history, second jobs in an industrial setting, and other environmental exposures that could contribute to respiratory illness should be investigated. The frequency and temporal sequence of respiratory symptoms and signs in relation to exposure are particularly important in assessing asthma, hypersensitivity pneumonitis, and TODS. For febrile illnesses, blood should be drawn, spun down, and serum frozen for subsequent serological testing, should the clinical course dictate obtaining a convalescent serum. Paired blood specimens offer the opportunity to measure changes in levels of specific circulating antibodies, enhancing diagnosis of sporadic, difficult to diagnose infectious diseases even when culture techniques have failed. The first examination of the farmer should assess respiratory status through a detailed examination, baseline spirometry, a chest radiograph if the patient is symptomatic, and testing for agricultural allergies using skin tests or detection of serum antibodies as indicated. A spirometer is a valuable diagnostic tool for any rural clinic; spirometry measurements should be assessed in terms of accepted standards. Most office spirometers can assess forced expiratory volume in one second (FEV,) and forced vital capacity (FVC). Forced expiratory flow rates, such as FEF at 25 to 75% of lung volume, also should be measured if possible. Diffusion capacity measurements, done at a pulmonary function laboratory, would be important if chronic hypersensitivity pneumonitis is suspected. Following the initial examination, checkups should be performed as dictated by symptoms, exposures, and lung function measurements, optimally on an annual basis. More detailed workups may be indicated for certain agricultural workers because of their health status or because of their occupational exposures. These groups include grain elevator workers, dairy farmers, and workers in swine or poultry confinement units; other farmers with regular exposure to dusts who also are smokers; and those with a history of bronchitis, asthma, or frequent respiratory infections or flu-like illnesses. In addition, routine examinations provide an excellent opportunity to provide educational materials on occupational exposures and on smoking cessation. The respiratory evaluation may also be psychologically beneficial for agricultural workers who feel that they are exposed to toxic substances or to unusually large quantities of dusts and gases, or that their respiratory condition is degenerating. Agricultural workers with chronic respiratory illness will require routine follow-up at a frequency determined by lung function and continued exposure. Prevention of further exposure to causative agents and elimination of smoking are crucial for control of most chronic respiratory diseases. Techniques for preventing exposure to specific agents are described in units discussing specific agents, and in units on exposure measurement and personal protective equipment. Every effort should be made to allow the patient to continue to work. However, if education, engineering controls, work practice changes, use of respirators, and medication do not control the respiratory response or prevent further deterioration of respiratory status, a job change may be necessary. IV. APPROACHES TO PREVENTION Because inhaled agricultural dusts and gases commonly produce debilitating acute respiratory illness, can cause chronic obstructive and restrictive pulmonary disease, and may be fatal, mitigation of exposure to these substances is crucial. Farmers often do not consider measures to protect their own health because of stoic attitude, lack of time, economic constraints, or lack of information. They are likely to place greater emphasis on the health of their livestock than on their own health. Health care providers can play an important role in preventing respiratory disease by educating themselves and their patients in causes and prevention of occupationally-induced respiratory illness. Using the units and brochures in this series is an excellent step in this direction. Health care providers also can be influential by encouraging farmers to apply preventive measures, and can refer farmers to helpful information sources. Table 2 Information Sources for the Agricultural Worker and Health Care Professional Agricultural Engineering Departments at land grant universities Agricultural Extension Service Local or regional pulmonary specialists Local practicing veterinarians Veterinary specialists (public health veterinarians, swine medicine specialists, and the like) The American Lung Association of lowa The Institute of Agricultural Medicine National Institute for Farm Safety, Inc. (a professional organization for state agricultural safety specialists and others interested in farm safety as well) The National Safety Council Who's Who in Agricultural Health and Safety (a directory published by, and available from, the American Council of Governmental Industrial Hygienists,)6500 Glenway Ave., Building D-7, Cincinnati, Ohio 45211, Phone (513)661-7881. Table 2 includes types of agencies and people who can provide specific information on farm management or engineering control procedures useful in reducing respiratory hazards, and also lists agencies and specialists that may be helpful to the health care professional assisting a particularly difficult case. Preventing harmful respiratory exposures in agriculture is not an easy task. The complexity of dust and gas mixtures, the potential synergistic effects of these substances, and the multiplicity of exposure circumstances work together to make prevention difficult. When indicated and if possible, agricultural environments should be assessed for presence of potentially harmful agents, both to protect persons from hazardous exposures and to assist in diagnosis of illness. Measurement of dusts and gases is described in Unit 8. Then, agricultural workers must guard their health in three ways: by preventing creation of harmful substances, by preventing substances from entering the air or removing them once they have become aerosolized, and by preventing inhalation of harmful substances. Engineering controls and management of the work process are preferred techniques for avoiding respiratory hazards. Preventing creation of substances hazardous to the respiratory system is the optimal solution. Proper storage of grain, hay, and silage helps prevent spoilage of these plant materials, eliminating growth of bacteria, fungi, and byproducts that are responsible for causing hypersensitivity pneumonitis and TODS. Livestock can be vaccinated to prevent certain infectious respiratory diseases in humans. If formation of harmful agents cannot be avoided, attempts should be made to prevent them from becoming aerosolized or to void buildings of aerosolized toxins. Ducting systems in grain elevators have been quite effective in reducing grain dust aerosolization. Building design and ventilation of livestock confinement operations are crucial for keeping dust and gas levels minimal. Nonairtight silos recently filled with silage must be well ventilated to rid them of NOx. Tractor cabs with filtered air reduce inhalation of field dusts. Often, specific steps cannot be taken to eliminate potentially hazardous substances, so agricultural workers must take steps to avoid their inhalation. Manure pits must never be entered because of the potential presence of deadly concentrations of H2S. Airtight silos must never be entered because of the asphyxiation hazard. Persons with documented episodes of hypersensitivity pneumonitis should avoid the environments and activities that induce illness. Field workers can avoid inhaling pesticides by vacating recently sprayed fields for the recommended time interval. Use of personal protective equipment should be considered as an ancillary or temporary measure because of problems with respirator use, including assuring that workers consistently use a well-fitting and well-maintained respirator that protects against all agents present. Use of respirators may be imperative for highly sensitive individuals or in certain agricultural settings. Persons entering confinement operations or moving grain are wise to wear mechanical filter respirators as a matter of course. Use of respirators is discussed in Unit 9. Preventive measures specific to major hazardous substances or exposure circumstances are discussed in Units 1-7. e תתתתתתתתתתתתתתתתתתתתThe National Dairy Database (1992)תתתתתתתתתתתתתתתתתתתת תתתתתתתתתתתתתתתתתתתתת\NDB\OCCSAFE\TEXT2\OF200300.TXTתתתתתתתתתתתתתתתתתתתתתת %f TITLE;AGRICULTURAL DUSTS AND GASES |
