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Biological effect on the body

Sensitiser A chemical that will cause an allergic reaction in a substantial
number of exposed people (e.g. isocyanates)

Teratogen A chemical that causes birth defects (e.g. thalidomide)

Chemicals may target specific organs such as the eye, skin, blood, liver,
kidneys, nervous system and lungs.
There are the factors affecting response to a substance:
- Dose: the amount of exposure to a chemical is the single most
significant factor of concern. There is a level of exposure for most chemicals
below which no adverse effects are likely to be observed.
- Toxicity: chemicals vary widely in how toxic (poisonous) they are.
Exposure to small amounts of highly toxic chemicals can be a greater danger than
exposure to large amounts of less toxic chemicals.
- Duration and frequency: one-time exposures that are of short duration
are of less concern than multiple exposures of longer duration, all other factors
being equal. Thus, when there has been a chemical exposure, it is important to
know its duration and frequency.
- Synergistic effects: synergism occurs when exposure to two or more
chemicals at a time results in health effects that are greater than the sum of the
effects of the individual chemicals. For example, there is a much higher incidence
of lung cancer resulting from occupational exposure to asbestos in smokers
(compared with exposed non-smokers).
- Individual characteristics: each person is unique. While there are
many similarities in response to chemical exposures, responses may vary
dramatically among individuals. For example, males and females can react

differently and special concern is afforded to pregnant employees. Some
individuals are allergic or hypersensitive to certain chemicals.
Human health risk assessments of chemicals can be performed to evaluate
past, current and even future exposures to any chemical found in air, soil, water,
food, consumer products or other materials. They can be quantitative or qualitative
in nature. Risk assessments are often limited by a lack of complete information. To
be protective of public health, risk assessments are typically performed in a manner
that is unlikely to underestimate the actual risk.
Regardless, chemical risk assessments rely on scientific understanding of
pollutant behaviour, exposure, dose and toxicity. In general terms, risk depends on
the following factors:
• the amount of a chemical present in an environmental medium (e.g. soil,
water, air), food and/or a product;
• the amount of contact (exposure) a person has with the pollutant in the
medium; and
• the toxicity of the chemical.

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