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8.2 Toxic and Hazardous Substances
This lesson covers how the body is exposed to toxic substances, what they do, how exposure is reduced and how it is measured.
Key terms
| Term | Meaning |
|---|---|
| Latency | The time between exposure and the first sign of an effect. |
| Local effect | Damage where the substance meets the body. |
| Systemic effect | The substance is absorbed into the bloodstream and damages internal organs. |
| Odour threshold | The lowest concentration in air that can be smelled. It differs widely between people. |
| Olfactory fatigue | A fast loss of the ability to smell a strong odour. |
| Permissible exposure limit (PEL) | An OSHA limit on exposure, usually the concentration in air averaged over a period of time. |
| Potentiation | A second chemical that makes the first more harmful. |
| Synergism | Chemicals acting together to give an effect greater than the sum of their separate effects. |
How the body is exposed
- Inhalation is the most common. Inhaled material may lodge in the lungs and do harm.
- Skin contact. Some substances are caustic and burn the skin. Others are irritants that leave it dry and cracked. Cracked or cut skin lets substances reach the blood more easily.
- Eye contact. Some substances irritate or burn the eye and may be absorbed.
- Ingestion is seldom deliberate, but it happens when substances are left on hands, food or drink.
- Smell and taste. If you can smell a substance you are breathing it in, but many substances have no smell, so odour is not a reliable test. Many chemicals leave a taste if swallowed.
Effects on the body
- Carcinogens cause cancer, the uncontrolled growth and spread of abnormal cells.
- Mutagens change genes.
- Reproductive toxicants can cause infertility, disrupted menstrual cycles, harm to the fetus, stillbirth and birth defects. Generally, a chemical that causes health problems in a pregnant woman can harm the fetus. In men some chemicals lower sperm count and cause infertility or loss of sex drive.
- Combined exposure to more than one chemical can lead to synergism.
- People differ in their traits, so one person's reaction to a chemical differs from another's.
Reducing exposure
Workers who know which toxic materials they may meet take more care, and the employer must train every affected worker. Engineering controls reduce the hazard at the source:
- Substitution, using a less hazardous substance.
- Enclosure of the process or equipment, so that only trained people have access.
- Local exhaust ventilation, a hood or fan placed at the source to capture contaminated air or particles before they spread.
- General ventilation, continuous ventilation to keep levels below a hazardous concentration.
Use PPE when engineering controls are not enough.
Measuring and monitoring exposure
Exposure limits show the levels of exposure that should not harm. Chronic effects may appear only after years or decades. Limits do not take into account the interaction of two or more chemicals. Exposure is measured by air or environmental monitoring, or sampling. Biological sampling, by tests on blood and urine, is required where certain toxic substances exceed set levels in the air.
A study aid, not published or endorsed by IOSH or OSHA. Laws and limits differ between countries.