Inorganic agricultural dust exposure causes pneumoconiosis among farmworkers

Early studies of agricultural respiratory diseases focused on allergic disorders due to organic dust exposure. However, agricultural workers in dry climate regions are exposed to substantial concentrations of inorganic dusts from agricultural soils. Exposures to inorganic dusts are dependent on the specific crop and task, but are commonly several milligrams of respirable dust per cubic millimeter. In vitro toxicity studies show the dust’s cytotoxicity to be intermediate between controls and crystalline silica. However, in some assays of reactive oxygen species generation, such as H(2)O(2), hydroxyl radical, and nuclear factor kappaB generation, the agricultural dusts are more potent than silica. A recent study of human lung samples among deceased Latino males characterized the deposition of agricultural dusts in the lung and the pulmonary response to these dusts. Careful histologic analyses in this study demonstrated that farmwork was significantly associated with mineral dust small airways disease and pneumoconiosis (macules and/or nodules). These associations persisted in multivariate analysis. Cigarette smoking was independently associated with these outcomes, but the interaction of mineral dust and smoking was not significant. Limited studies of farmworkers exposed to inorganic dusts show respiratory symptoms and restrictive pulmonary function with exposure. Overall, the evidence supports a causal association of mineral dust exposure and pneumoconiosis. Inorganic mineral dusts should no longer be considered merely a nuisance, but rather a cause of mixed-dust pneumoconiosis. The prevalence and natural history of this disorder are unknown. – NCBI Resources

Farm Respiratory Protection

Farming is filled with respiratory hazards: pesticide vapors, dusty fields, dangerous hydrogen sulfide accumulations in manure pits and pump sumps, nitrogen dioxide in conventional silos, and many others. Farmer’s Lung and Organic Dust Toxicity Syndrome (ODTS) are allergic reactions to dust from moldy hay or grain and may result in costly medical treatment, permanent lung damage or death.

In many cases an inexpensive respirator could prevent farmers from acquiring nagging, permanent lung damage caused by long-term exposure to dusts, mists, gases, and vapors. This fact sheet examines categories and types of farm respiratory protection and the proper use of these devices.

Pinpoint the Hazard

The first step to choosing a respirator is determining the type of respiratory hazard. There are three basic categories of respiratory hazards on the farm. The first category, particulate contaminants, includes dusts, mists, and fumes. Dusts are usually the largest particles, but not all dusts can be seen with the naked eye. Mold spores, for example, are microscopic. They are released when moldy hay, silage, or grain is disturbed. Mists are suspended liquid droplets and are usually found near mixing, spraying, and cleaning operations. Fumes are solid particles of evaporated metal. They are microscopic as well and are formed during activities such as welding.

The second category of respiratory hazard is gases and vapors. Gases are chemicals that are gaseous at ambient (room) temperature. Examples include hydrogen sulfide, the deadly manure pit gas; nitrogen dioxide, which can be found in conventional silos; and carbon monoxide from operating internal combustion engines. Vapors are released from liquids, such as pesticides, paints, adhesives, and lacquer thinner.

The third category of respiratory hazard is an oxygen deficient atmosphere. Examples of oxygen deficient atmospheres include manure storage, oxygen limiting (sealed) silos and controlled atmosphere (CA) storage for fruits and vegetables. In such structures, the oxygen content of breathable air, normally about 21%, is reduced to levels as low as 5%. The reduction in oxygen may occur deliberately, such as with CA storage, or oxygen may be displaced by other gases as in manure storage and conventional silos.

Once you’ve pinpointed the hazard (or hazards), and before resorting to a respirator, try to reduce or eliminate the source of the problem. For example, use a different management practice when harvesting and storing crops to reduce dust and mold. Provide improved ventilation in your barn or work outdoors instead of in an enclosed building. Another possibility may be to use a non-toxic, less toxic, or less volatile pesticide. After you have tried to reduce or eliminate the hazard, if you are still at risk, use a respirator.

Nuisance Dust Mask

A nuisance dust mask is not an approved respirator. This type of mask offers some protection against large particles of dust but not against smaller particles that may enter deeply into the lungs and cause respiratory distress or disease. Nuisance dust masks most often are constructed of a very light paper filter and have only a single, thin strap. These masks are normally of the one-size-fits-all variety and the thin strap is not adjustable, making a good fit difficult at best (Figure 1). They are easily stretched and distorted by putting on and taking off the mask. Nuisance dust masks are best worn by persons with no existing respiratory distress or breathing limitations for short-term exposure to light levels of non-toxic dusts, such as sweeping out a garage or shop floor.

Approved Respirators Identified

There is no such thing as an all-purpose respirator. Specific respirators are used for specific contaminants or atmospheres. Choose your respirator carefully. Use a respirator approved by the National Institute for Occupational Safety and Health (NIOSH). Older style NIOSH approved respirators or filters have a number preceded by the prefix “TC”. Newer models of approved respiratory protection have the NIOSH TC approval number followed by a description of the respirator. An example is: “NIOSH TC 23C dual cartridge half mask with disposable filter used for pesticides and ammonia.”

The newer respirators are also rated according to the filter’s efficiency in reducing dust, mists, and fumes and their time use limits against oil based chemicals or pesticides in the atmosphere. Filtering efficiencies can be 95%, 99%, or 99.97%. Respirators rated 99.97% effective are given a rating of 100% as a practical matter. A respirator with a designation of N, R, or P indicates: not resistant to airborne oils, plugs quickly (N); resistant to airborne oils for up to 8 hours (R); or oil proof, possibly resistant to airborne oils for up to 8 hours, change filter every 40 hours of use or 30 days, whichever comes first (P). The filtering efficiency rating and resistance to oils rating can appear independently on the respiratory unit, pre-filters, cartridges, the packaging, and in advertisements. In addition to the TC number, approved respirators always have at least two elastic straps or a head band (Figure 2).

Categories and Types of Respirators

There are two categories of respirators: air purifying and supplied air. Air-purifying respiratorsare equipped with filters through which the user breathes. Important: These respirators do not supply oxygen. Therefore, they should not be worn in areas considered immediately dangerous to life or health (IDLH), such as oxygen-deficient areas (oxygen-limiting silos, for example) or highly toxic atmospheres (manure storage pits). Air-purifying respirators are good in areas such as barn lofts with moldy hay, fields during tilling or pesticide application, or construction sites where fiberglass or wood dusts are likely to be found. For most air-purifying respirators, the user must pull air through the filter with their own breathing. This type of respirator is often referred to as a “negative pressure” respirator because the user must draw in oxygen (inhalation) through the respiratory unit. Negative pressure air-purifying respirators often put added stress on you. If you suffer or suspect that you suffer from respiratory problems such as asthma, lung or cardiovascular disease, check with a doctor to make sure you are able to wear one. There are several types of air-purifying respirators.

Disposable Particulate Respirators

Disposable particulate respirators are an approved type of respirator but are also commonly referred to as dust masks, making it easy to confuse them with a nuisance dust mask. Disposable particulate respirators protect you from particulate contaminants such as dusts, mists, and sometimes fumes. The filters are made of a fibrous material that traps particles as you inhale. These respirators are useful during operations such as haying, harvesting, tilling dusty fields, applying fertilizer and lime, grinding feed, and sweeping. Both disposable and reusable masks are available. Disposable masks are more convenient—you simply throw them away when they’re saturated. Reusable masks, on the other hand, may save you money in the long run and create less waste.

Filters and disposable masks should be replaced when breathing becomes too labored, when the mask loses its shape and no longer seals well to your face, or if you taste or smell the substance.Remember: a “nuisance dust mask” is not considered a respirator.

Chemical Cartridge Respirators

Chemical cartridge respirators filter out low concentrations of toxic gases and vapors. An absorbent material such as activated charcoal absorbs contaminants from inhaled air. These masks can also be equipped with particulate filters, so if you’ll be exposed to gases or vapors and dusts or mists, this is the kind of respirator you should wear.

Figure 3. Full-face cartridge type respirator.

There are half-mask models and full-face models; the latter provides eye and face protection as well. The half-masks are also available in disposable or reusable models. Full-face models (Figure 3) provide considerably more protection against contaminants than halfmask models because they seal to the face better. The filtering cartridges for these respirators usually screw onto the front of the mask. The cartridges are changeable, so if you have a reusable mask you can use it for any gas or vapor contaminant, provided you have the right cartridge.

Cartridges should be replaced after eight hours’ use or when “breakthrough” occurs—that is, when you begin to smell or taste the contaminant or when dizziness or irritation occurs. Make sure the cartridge brand matches the respirator brand. Manufacturers use different threads which may prevent mismatched brands (respirators and cartridges) from sealing properly. Chemical cartridge respirators should not be worn in areas considered immediately dangerous to life or health (IDLH).

Read further at PennState Extension

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