We know that inhaling particles can be bad for our health, but do we really know why, or what dose, is needed for harm to occur? Depending on the particle size, chemical composition and dose, our lungs and other organs can be affected in very different ways. Let’s take a look at some of the variables which determine how our bodies might react to the tiny solid particles suspended in the air, commonly known as dust.
Dust particles are either “inorganic” or “organic,” depending on their source. Inorganic dusts such as silica, asbestos, and coal usually come from grinding metals or minerals. Organic dusts from plants or animals have a wide variety of compounds from both the source and from additional microbes and the toxic substances given off by microbes (histoplasmosis, psittacosis, and Q Fever).
The size of particles is directly linked to their potential for causing health problems. Fine particles with a diameter of 2.5 um or less (PM2.5) are the most problematic because they are small enough to reach the depths of our lungs and even pass into our bloodstream. Larger particles (PM10-2.5) can be irritating to our eyes, nose, and throat but are less likely to cause overwhelming illness.
Our lungs are constantly bombarded by the dust we breathe. Luckily, we also have protective mechanisms designed to prevent dust particles from settling deep within our respiratory system. If dust only gets as far as the nose, inflamed mucous membranes (rhinitis) result. Particles that reach deeper air passages can inflame the trachea (tracheitis) or bronchi (bronchitis).
A healthy respiratory system can effectively prevent penetration of particles into the most recessed tissue — the lungs. For example, a coal miner may inhale 1,000 g of dust during her working lifetime, yet on autopsy there could be less than 40 g of coal dust residue detected in her lungs. Some people, however, have less effective elimination by their nose or throat, and dust can potentially settle in the air exchange sacs in lung tissue.
In addition to particle size, other factors influence whether a harmful particle will reach the lungs. For example, associated chemicals such as nicotine, or more direct breathing pathways through the mouth, can impair the ability of the respiratory tract to prevent deeper penetration into the lungs, where the most damaging changes can occur.
The amount and kind of particles inhaled also influence how serious the lung injury will be. For example, some inorganic particles such as silica cause the defending lung cells to die and give off additional toxic substances, hastening the formation of inelastic scar tissue in the lung. If scaring is extensive, lung function can be seriously impaired.
Luckily, not all inhaled particles reaching the lungs produce scar tissue. Dusts such as carbon and iron remain within lung cells until they die normally. The released particles are then ingested by other lung cells lining the inner walls of the airways, only causing mild, non-scarring damage.
Some inhaled particles are of a size and composition where they can cross into the circulation and reach distant organs such as the brain or kidneys, impairing tissues far from the lungs.
To avoid the myriad of respiratory, cardiac, and other potential problems caused by large doses of dust, engineering controls should be strictly observed when there are known high or ongoing dust exposures. Some of these strategies are:
- Use of wet mopping
- Enclosures with negative air pressure and adequate humidification to decrease suspension
- Exhausting dust-laden air through a filtering system before emission
- Use of vacuums
- Good surface cleaning
- Efficient storage, transportation, and disposal of waste.