Occupational Lung Diseases - An introduction

Exposure to harmful particles, chemicals, vapors or gases while at work can lead to a variety of health problems including diseases like mesothelioma, asbestosis and silicosis. Some of the more common irritants include organic materials (animal dander, grain dust), chemicals (beryllium), and asbestos particles.

Effects of Particle Exposure

Different types of particles produce different reactions in the body including:

  • Allergies - Often associated with animal dander.
  • Lung Irritation - This is often the result of chronic exposure to asbestos or other industrial dusts
  • Cancer - Common cancers include lung cancer and mesothelioma (cancer of the lining of the chest and lungs)
  • Apoptosis - The death of cells located throughout airways and within the alveoli

Common Occupational Lung Diseases and Their Causes

  • Asbestosis, caused by exposure to asbestos particles. Often found among people who worked in shipyards, asbestos mines, and factories that refined or used asbestos to manufacture products.
  • Black lung (Coalworker's pneumoconiosis) which affects coal workers
  • Chronic Beryllium disease (CBD), which affects workers in a variety of metallurgical occupations
  • Byssinosis (brown lung disease), often occurs in cotton and textile workers when bacteria released from cotton or other materials is inhaled and grows with the lungs. This is often associated with poor ventilation systems.
  • Hypersensitivity pneumonitis, this can affect people who work in office buildings whose air-conditioning systems are contaminated by certain fungi and bacteria.
  • Occupational asthma, can affect people who work with a variety of materials. This includes animals (dander), carbamates (urethanes), dyes, epoxy resins and enzymes used in detergent, leather goods, latex, and automotive paints
  • Silicosis often developed by people who worked with clay, sand and stone dust including miners, stone cutters and sandblasters.

How Diseases Develop

Pneumoconiosis is the classification of diseases that develop as the result of occupational exposure to dust. Occupational lung diseases develop based on the size and type of particles inhaled and where the inhaled particle end up. Larger particles are more likely to get stuck in the nose and larger airways but smaller particles can reach the alveoli where they can potentially be absorbed into the bloodstream.

When inhaled particles come in contact with the wall of the airway they do not become airborne again. This is called deposition and can occur in one of four ways:

  • Sedimentation: When gravity causes particles to settle, tends to occur in larger airways.
  • Inertial impaction: Often occurs in the nose and larger airways, it happens when an airway changes direction
  • Interception: This form of deposition occurs with fibrous dust particles (including asbestos fibers) or any other irregular shaped particles. Due to their shape they often avoid deposition by sedimentation or inertial impaction but are deposited in the walls of the bronchioles which are lined with epithelial cells.
  • Diffusion: Behavior of small aerosol particles which encounter and are affected by molecules of air.

Alveolar deposition, the process of particles settling in the alveoli, often occurs with particle diameters of between 1 and 7 microns. During regular breathing (at rest) about 10% of compact particles of 0.5 to 1 micron diameter are deposited in the alveoli with the vast majority being exhaled. More on the etiology of mesothelioma.

Defense Mechanisms

The nose is able to filter the majority of compact particles larger than 20 microns and about half of the particles 5 microns in diameter. However there is a wide variation in how efficiently an individual is able to filter particles and filtering rates vary depending on breathing rate and whether a person is resting because the mouth lacks these filters which makes a person more susceptible to deposition.

The lungs feature three defense mechanisms including:

  • Mucus, a secretion produced by mucous membranes, that protects epithelial cells by coating foreign particles so that they can be coughed out of the body.
  • Cilia, microscopic hairs that line the airways and attempt to brush foreign particles out of the lungs
  • Macrophages, special cells (alveolar macrophage) that attempt to engulf and digest particles and can signal lymphocytes and other immune system cells to respond to specific pathogens. Human macrophage cells are around 21 microns in diameter and are capable of digesting a number of particles but they cannot digest asbestos fibers which can cause the cell to burst.

Preventing Occupational Lung Disease

Reducing exposure to harmful agents in the workplace, in addition to a reduction in cigarette smoking, can help prevent a major proportion of lung disease. To prevent occupational lung diseases, a comprehensive strategy is required - one which combines medical and environmental surveillance, reduction and removal of exposures, promotion of health and education, regulation, research and enforcement. None of the individual strategy components should be ignored if the effectiveness of prevention measures is to be maintained.

The main objective of a strategy for the preventing occupational lung disease should be to protect workers from being exposed to dangerous levels of hazardous substances. To implement the strategy, changes in work practices and technological controls are often required. Employers are encouraged to establish comprehensive information and training programs and to develop on the basis of sound educational principles to inform workers, engineers, managers and healthcare professionals about the dangers of airborne particles and control measures installed to mitigate them.

Many public health professionals feel systematic studies are required to get reliable data about occupations and industries that are at a risk for occupational lung disease. Also required are studies that can help measure the incidence and prevalence of ailments in all types of industries that use hazardous materials.

An essential requirement is to establish stringent and medically-based regulation of exposure levels for all types of substances known to cause occupational lung disease. In situations where not much information is available about safe levels, it is necessary to expedite research in order to provide an appropriate platform for effective regulation. In some areas OSHA regulations fail to reflect existing medical knowledge (for instance, cases where levels recommended by NIOSH are more stringent). When the regulatory agencies and the plant industrial hygienists develop acceptable exposure levels they should consider all potential diseases caused by a given substance. To prevent exposure to respiratory toxins in the workplace, there are specific steps with the following recommendations:

  • Substitution is the best way to prevent hazardous emissions (i.e. replacing hazardous substances with those that are less hazardous).
  • Imposition of rigorous engineering controls is the second best way to prevent airborne exposure. This would include ventilation and process design which does not allow release of gases and toxic particles into the air.
  • Use of protective gear and respirators has been shown to be the least satisfactory method of preventing occupational respiratory exposures. This method should be used only if other methods cannot cope with the problem or hazard.
  • All approaches used for reducing exposure to hazardous substances in the workplace should be supported by stringent enforcement of law and through periodic review of current legal standards that regulate occupational exposure.

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