Environmental hazards are things found in air, water, and soil that negatively impact living beings. These health hazards are assessed in terms of dose-response, exposure and risk.

Dose-Response Assessment
Paracelsus, the Swiss physician and alchemist, the "father" of modern toxicology (1493 – 1541) said, "The dose makes the poison." In other words, for most toxic substances, the amount of a substance a person is exposed to is as important as how toxic the substance might be. For example, small doses of aspirin can be beneficial to people, but at very high doses, this common medicine can be lethal. Individual responses to dose often vary. Even in very low doses, aspirin is deadly for some people.

Exposure Assessment
People can be exposed to environmental hazards in three ways:

1. Absorption through the skin
2. Inhalation (entry through the respiratory system)
3. Entry through the mouth and digestive system

Most hazardous substances are more likely to be absorbed into the body by one means of exposure than by another. Knowing how a hazardous substance is likely to enter the body aids in assessing our potential for exposure.

Risk Characterization
Environmental hazards are often characterized by the risk they pose to human health as well as by their effects on our environment. Risk is assessed by the combined effect of the toxicity of the substance and the amount of exposure. At least some exposure and some toxicity are required to result in a risk. For example, if your exposure to a non-toxic substance is high, there is no risk. By the same token, if the substance is very toxic but no one is exposed to it, there is no risk.  Thus -

RISK = TOXICITY x EXPOSURE

It is very important to be aware of how to minimize the risks of environmental health hazards.  In the following lessons, we will talk about hazards and how to avoid them.