Toxicity of Chemicals
Latency: How Long Does it Take for a Toxic Effect to Occur?
The effects of toxic substances may appear immediately or soon after exposure, or they may take many years to appear.
Acute Exposure: Acute exposure is a single exposure or a few exposures. Acute effects are those which occur following acute exposures. Acute effects can occur immediately, or be delayed and occur days or weeks after exposure.
Chronic Exposure: Chronic exposure is repeated exposure that occurs over months and years. Chronic effects are those which occur following chronic exposures, and so are always delayed.
A toxic chemical may cause acute effects, chronic effects or both. For example, if you inhale solvents on the job, you may experience acute effects such as headaches and dizziness which go away at the end of the day. Over months, you may begin to develop chronic effects such as liver and kidney damage.
Latency Period: The latency period is the delay between the beginning of exposure and the appearance of disease caused by that exposure. Some chronic effects caused by chemicals, such as cancer, have very long latency periods. Cancer has been known to develop as long as 40 years after a worker's first exposure to a cancer-causing chemical.
Since chronic diseases develop gradually, it may be some time before it is detected. It is important for physicians to know what chronic effects might be caused by the substances used on the job.
Click on the link below to review a table of the differences between acute and chronic effects.
| Acute | Chronic |
|---|---|
| Occurs immediately or soon after exposure (short latency). | Occurs over time or long after exposure (long latency). |
| Often involves a high exposure (large dose) over a short period. | Often involves low exposures (small doses) over a long period. |
| Often reversible after exposure stops. | Many effects are not reversible. |
| Can be minor or severe. For example, a small amount of ammonia can cause throat or eye irritation; larger amounts can be serious or even fatal. | Chronic effects are still unknown for many chemcials. For example, most chemicals have not been tested for cancer or reproductive effects. |
| Relationship between chemical exposure and symptoms is generally, although not always, obvious. | It may be difficult to establish the relationship between chemical exposure and illness because of the long time delay or latency. |
| Knowledge often based on human exposure. | Knowledge often based on animal studies. |
Knowledge Check Choose the best answer for the question.
3-5. The delay between the beginning of exposure and the appearance of disease caused by that exposure is called the _____.
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