Chapter 33

• Occupational toxicology is the application of the principles and methodology of toxicology toward chemical and biological hazards encountered at work.
• In occupational environments, exposure is often used as a surrogate for dose.
• Occupational exposure limits do not correspond to the level of exposure below which the probability of impairing the health of the exposed workers is acceptable.
• Diseases arising in occupational environments involve exposure primarily through inhalation, ingestion, or dermal absorption.

Occupational toxicology is the application of the principles and methodology of toxicology toward chemical and biological hazards encountered at work. The objective of the occupational toxicologist is to prevent adverse health effects in workers that result from their work environment. Because the work environment often presents exposures to complex mixtures, the occupational toxicologist must also recognize exposure combinations that are particularly hazardous.

It is often difficult to establish a causal link between a worker's illness and job. First, the clinical expressions of occupationally induced diseases are often indistinguishable from those arising from nonoccupational causes. Second, there may be a long interval between exposure and the expression of disease. Third, diseases of occupational origin may be multifactorial with personal or other environmental factors contributing to the disease process.

### Determinants of Dose

Dose is defined as the amount of toxicant that reaches the target tissue over a defined time span. In occupational environments, exposure is often used as a surrogate for dose. The response to a toxic agent is dependent on both host factors and dose. Figure 33–1 illustrates the pathway from exposure to subclinical disease or adverse health effect and suggests that there are important modifying factors: contemporaneous exposures, genetic susceptibility, age, gender, nutritional status, and behavioral factors. These modifying factors can influence whether a worker remains healthy, develops subclinical disease that is repaired, or progresses to illness. As illustrated in Figure 33–1, the dose is a function of exposure concentration, exposure duration, and exposure frequency. Individual and environmental characteristics also can affect dose. Table 33–1 indicates determinants of dose for exposure via the inhalation and dermal routes.

###### Figure 33-1

Pathway from exposure to disease, showing modifying factors and opportunities for intervention.

Table 33–1 Determinants of toxicant dose.

### Occupational Exposure Limits

Workplace exposure limits exist for ...

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