In occupational health, understanding the difference between chronic and acute effects and the concept of dose is fundamental for protecting workers from hazardous exposures. These concepts are crucial to developing effective safety protocols and ensuring long-term health in the workplace. Today, we’re diving into the critical distinctions between chronic and acute effects and exploring how the concept of dose influences these outcomes.
In this post, we’ll examine chronic and acute effects, how they differ, and why the amount of exposure (dose) is a crucial factor in determining the impact of hazardous substances. By the end, you’ll clearly understand these essential concepts and how to apply them to enhance workplace safety.
What You’ll Learn
- Chronic vs. Acute Effects: Understand the differences between chronic and acute health effects and how each type of exposure impacts worker health.
- The Concept of Dose: Learn about the concept of dose and its critical role in determining the severity and type of health effects from exposure to hazardous substances.
- Applying the Concepts: Discover practical strategies for managing and mitigating chronic and acute workplace exposure risks.
Introduction
The American Industrial Hygiene Association (AIHA) recently announced new guidelines for developing workplace health metrics to help prevent illness and injury (EHS Today, 2021). The leading health outcomes addressed acute metrics such as eye irritation, dermatitis, or metal fume fever. They can also be chronic, such as elevated blood pressure, hearing loss, or cancer.
Chronic Effects
So, what are chronic effects? Chronic effects have a long latency between exposure and impact, are long-lasting, and may be permanent (although not necessarily). Some examples include:
- Pneumoconiosis (dusty lungs) from exposure to coal dust.
- Silicosis after exposure to quartz dust.
- Manganese dust or fume exposure may damage the central nervous system.
- Asbestosis and mesothelioma after asbestos exposure.
Acute Effects
Acute health effects occur during or soon after exposure and last briefly. Some examples of acute effects are:
- Lacrimation (tearing) of the eye and irritation of the respiratory tract from exposure to and inhalation of chlorine gas
- Burns of the skin from a spill of strong acid or alkali
- Respiratory sensitization is caused by ozone from photocopiers or the generation of a welding arc.
An acute dose results in the rapid accumulation of a substance over a relatively short time. A chronic dose occurs over a longer time frame and can take two forms, depending on whether the substance is metabolized, excreted, or accumulated and stored.
If no elimination or excretion occurs, the accumulated dose will be additive. But if the substance is partly metabolized or excreted, the accumulated dose will rise and fall – accumulating more slowly.
The Concept of Dose
The concept of dose is paramount for industrial hygiene and risk management (Dawson et al., 2021). Dose refers to the amount of a substance we are exposed to and is a combination of the concentration and duration of exposure.
The dose depends on the following factors:
- Rate of absorption (depending on the route of entry).
- Blood perfusion rate to the organ under consideration.
- Rate of passage of the chemical (and its metabolites) across the cell membrane.
- The volume of distribution for the chemical.
- Rate of biotransformation of the chemical.
- Degree of binding of the chemical (and its metabolites) to tissues and plasma proteins.
- Rates of excretion of the chemical (and its metabolites).
Generally, an increase in dose will increase the response. This is known as the dose-response relationship. The relationship may not be linear, where the dose is proportional to the response, but it mostly has a sigmoid or curved shape.
This means that exposure at a particular dose may not lead to a response, and there may be a dose threshold. A dose threshold assumes the human body can cope with the exposure without effect.
These dose-response relationships are used in toxicology to estimate health effects from exposure to particular concentrations of substances over time. Scientists carrying out experimental toxicology use test animals (e.g., rats, mice, and rabbits) and expose them to particular toxic substances via alternative routes of entry for different durations.
Summary
Industrial hygiene combines the sciences and arts to anticipate, identify, evaluate, and control hazards that may impact workers’ health. Depending on the hazard and the exposure, individual workers may experience different impacts, which could be acute or chronic. It is important to take both aspects of exposure and the associated effects into account when evaluating the risk to workers.
Helpful Resources
- Occupational Health and Safety Management: A Practical Approach, by Charles Reese
- Fundamentals of Industrial Hygiene, by Barbara Plog
- Metals in the Workplace Blog Post, by Megan Tranter
Bibliography
Dawson, B., Dotson, K., Grimsley, F., Grumbles, T., Mansdorf, Z., Roskelley, D., Sahmel, J., Tresider, N., & Tsai, C. (2021). Occupational and Industrial Hygiene as a Profession: Yesterday, Today and Tomorrow. In Patty’s Industrial Hygiene, Hazard Recognition (p. 418). John Wiley & Sons. https://books.google.com/books?hl=en&lr=&id=mgsmEAAAQBAJ&oi=fnd&pg=PA3&dq=industrial+hygiene+dose&ots=m7ivnMQKjv&sig=0G8RU4KCHyBto8ttT1fGH1mRbBI#v=onepage&q=industrial%20hygiene%20dose&f=false
EHS Today. (2021, June 2). Occupational Health Experts Offer Guidelines to Prevent Workplace Illness and Injury. EHS Today. https://www.ehstoday.com/industrial-hygiene/article/21165463/occupational-health-experts-offer-guidelines-to-prevent-workplace-illness-and-injury
