Toxic and Hazardous Chemicals
What Makes a Chemical Toxic?
The toxicity of a substance is its ability to cause harmful effects. These effects can strike a single cell, a group of cells, an organ system, or the entire body. A toxic effect may be visible damage, or a decrease in performance or function measurable only by a test. All chemicals can cause harm. When only a very large amount of the chemical can cause damage, the chemical is considered to be practically non-toxic. When a tiny amount is harmful, the chemical is considered to be highly toxic.
The toxicity of a substance depends on three factors: its chemical structure, the extent to which the substance is absorbed by the body, and the body's ability to detoxify the substance (change it into less toxic substances) and eliminate it from the body.
A chemical is determined to be a hazard depending on the following factors:
- Toxicity: how much of the substance is required to cause harm
- Route of exposure: The route of exposure, such as inhalation, ingestion, or skin contact
- Dose: how much enters your body
- Duration: the length of time you are exposed
- Reaction and interaction: other substances you are exposed to at the same time, and,
- Age, sex, and health status: age, sex, and underlying health conditions can influence how susceptible a person is to the toxic effects of a chemical
- Metabolism: the way a chemical is metabolized by the body can determine how quickly it is eliminated and whether it is converted into a more or less toxic substance
- Interactions with other substances: interactions with other substances in the body, such as drugs, to produce toxic effects that are greater than the sum of their individual effects
Some chemicals are hazardous because of the risk of fire or explosion. These are important dangers, but are considered to be safety rather than toxic hazards. The factors of a toxic hazard are more fully explained below.
Why Are Some Chemicals More Harmful Than Others?
The most important factor in toxicity is the chemical structure of a substance (i.e., what it is made of), what atoms and molecules it contains and how they are arranged. Substances with similar structures often cause similar health problems. However, slight differences in chemical structure can lead to large differences in the type of health effect produced. For example, silica in one form (amorphous) has little effect on health, and is allowed to be present in the workplace at relatively high levels. After it is heated, however, it turns into another form of silica (crystalline) that causes serious lung damage at levels 200 times lower than amorphous silica.
Knowledge Check Choose the best answer for the question.
3-2. Slight differences in _____ of chemicals can lead to large differences in the type of health effect produced.
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