Understanding how hazardous substances enter the body is a cornerstone of occupational health and safety. The routes of entry: how toxins, chemicals, and other harmful agents gain access to our bodies—are critical to identifying risks and implementing effective protective measures. Today, we’re delving into the essential topic of routes of entry and how this knowledge can help safeguard worker health.
In this post, we’ll explore the various routes through which hazardous substances can enter the body, the health risks associated with each route, and practical strategies to mitigate these risks. By the end, you’ll be equipped with the knowledge to enhance safety protocols and protect yourself and your colleagues from harmful exposures.
What You’ll Learn
- Understanding Routes of Entry: Learn how hazardous substances can enter the body, including inhalation, ingestion, skin absorption, and injection.
- Health Risks Associated with Each Route: Discover the health risks linked to each entry route and how they can impact overall well-being.
- Mitigation Strategies: Explore practical strategies and best practices for preventing and controlling exposure through various routes of entry in the workplace.
Introduction
A substance will only cause an effect if it comes into contact with the human body. The main ways this can occur are through:
- Inhalation of the substance.
- Absorption through the skin or mucous membranes.
- Ingestion through the gastrointestinal tract.
- Injection through the skin.
These are called the routes of entry. While many industrial hygiene hazards have a single route of entry, some (such as nanoparticles) may enter the body through multiple routes of entry (“Routes of Exposures and Toxicity of Nanoparticles,” 2020).
Inhalation
The most common way a substance enters the body is through inhalation. This airborne substance may be a gas, vapor, dust, mist, fume, or aerosol. At rest, a healthy person will breathe about 6 liters of air each minute. Work requiring high metabolic energy expenditure, such as shoveling, pushing a wheelbarrow, or lifting objects, may increase the flow to 150 liters per minute.
Even wearing respiratory protection such as air-purifying respirators will increase the depth of breathing as air must be drawn through the filtering material. Since inhalation is a significant source of exposure, occupational hazard risk assessments often use data from the Globally Harmonized System (GHS) for the classification and labeling of chemicals, which includes consideration of the route of entry (Bakri et al., 2020).
Absorption
Absorption is the second most frequent route of entry of substances into the body. The skin protects against external factors such as the sun, heat, cold, bacteria, and chemicals. However, some of the following chemicals can penetrate the skin:
- Fat or lipid-soluble substances.
- Oleoresins of some poisonous plants, such as poison ivy.
- Organic solvents such s acetone, toluene, and benzene.
- Salts of heavy metals, such as mercury.
Acids and alkalis may burn the skin. Sensitizing agents such as isocyanates found in polyurethane manufacture and some paints can cause reddening or irritation to the skin. Non-ionizing radiation from the sun can burn the skin. Sharp objects and needles can penetrate the physical barrier of the skin and inject substances directly into the body. Broken or damaged skin provides an easy passage for substances to enter the body.
Substances may also be absorbed through the mucous membranes of the nose, throat, and eyes. This is particularly true for water-soluble gases such as formaldehyde, which is used in histology laboratories (as formalin) to fix specimens and as a glue or resin component.
Ingestion
Ingestion is generally considered the least common route of entry, although some have recently questioned this (Guidotti, 2019). It typically occurs through substandard personal hygiene or by eating/drinking unknown substances. Failing to wash hands, eating, or smoking after handling a substance can leave a residue on the hands that can then be accidentally ingested.
Another more insidious form of ingestion occurs because of the standard clearance mechanism of the lungs. The lining of the trachea is constructed from finger-like projections called cilia, which are covered in a mucous membrane. The mucous collects foreign particles before they enter the lungs. As the contaminants are moved along the mucociliary escalation for elimination, they are swallowed and removed through the digestive system. This is one reason why asbestos workers have a higher-than-normal incidence of stomach cancer.
Injection
Sometimes, a substance may enter the body by unintentional injection or puncture through the skin. This may be caused by sharp objects such as needles (e.g., in a hospital setting, cleaning staff, waste disposal) or an injection process. Once in the bloodstream, the substance may be transported to any site or organ of the body.
Summary
Understanding the routes of entry is an essential concept in industrial hygiene. It helps anticipate and identify hazards, evaluate risk, and control exposure. When attempting to manage risk, the mechanism of the effect and the probability that this will occur must be known.
This begins by identifying where the substance or agent enters the body. The movement and metabolism of the substance through the body must also be known to determine the most likely response. We aim to reduce exposure to a level as low as reasonably achievable (ALARA).
Helpful Resources
- Occupational Health and Safety Management: A Practical Approach, by Charles Reese
- Fundamentals of Industrial Hygiene, by Barbara Plog
- Occupational Exposure Limits Blog Post, by Megan Tranter
Bibliography
Bakri, S. F. Z., Hariri, A., & Ismail, M. (2020). Occupational Health Risk Assessment of Inhalation Exposure to Welding Fumes. International Journal of Emerging Trends in Engineering Research, 8(1.2), 90-97. https://www.researchgate.net/profile/Siti_Zainal_Bakri/publication/344606348_Occupational_Health_Risk_Assessment_of_Inhalation_Exposure_to_Welding_Fumes/links/5f83fa92a6fdccfd7b5aa029/Occupational-Health-Risk-Assessment-of-Inhalation-Exposure-to-Welding-Fu
Guidotti, T. L. (Ed.). (2019). Another target organ? Archives of Environmental & Occupational Health, 74(5), 223-224. https://www.tandfonline.com/doi/pdf/10.1080/19338244.2019.1640926
Routes of Exposures and Toxicity of Nanoparticles. (2020). In K. Srikanth (Ed.), Model Organisms to Study Biological Activities and Toxicity of Nanoparticles (pp. 267-276). Springer. https://link.springer.com/chapter/10.1007/978-981-15-1702-0_13
