All matter and substances are composed of chemical elements and chemical compounds. Chemicals are the basic elements of life and the world around us. Materials made from chemicals are elements of our cars, clothing, furniture, tools and many other things we come in contact with daily. Most chemicals and compounds are beneficial to man. Some chemicals and compounds present either immediate danger or long term effect on health . Chemicals have been portrayed by news media , environmental groups, and lawmakers as a particularly harmful part of our health concerns. Today, public concern over chemicals is at an all-time high and there has been an increase in concern for the health of workers exposed to toxic chemicals. Employers and workers alike are emphasizing safe work environments by implementing the principles of industrial toxicology. Since the 1960s these concerns have been particularly apparent as the field has grown rapidly. Ideally all work environments should deal with chemicals that are considered safe and will have no harmful effects on the health of humans. However, no chemical can be considered safe because any chemical in a large enough amount can do some harm. Similarly, there is no precise level of chemical exposure that is safe for all people because individual human responses may vary significantly.

Chemicals cannot be simply classified as toxic or nontoxic because of variances in the dose level, the site of human contact with the chemical, the occupational hygiene of the worker and the general work environment, and other influences such as lifestyle, diet, heredity, age, sex, and resistance to disease. In combination, these variables may be synergistic, causing greater damage in their combined effect; or their effects may be antagonistic, so that they are less damaging together than separately.

The exposure to toxic substances usually involves mixtures; so the limits set by the government for single substance exposure should not be considered completely safe, but rather as tolerable levels. As a practical matter, it is desirable to achieve the lowest workplace concentration of a toxic material that is economically feasible.

There are over 3,000,000 registered chemical compounds. About 60,000 of these chemical compounds have significant economic value and are in the marketplace. An estimated 700 to 1000 new compounds enter the marketplace each year. There are published exposure standards for about 500 compounds. National Institute for Occupational safety and Health (NIOSH) has compiled a list of about 5,000 chemicals that have some inherent hazard.

In a given year, industrial facilities in the United States release almost 6 billion pounds of toxic substances into the environment. The Environmental Protection Agency (EPA) began measuring such emissions in 1987. Since that time the trend in toxic emissions has been downward. Even with downward trend, however, in a typical year toxic substances will be released into the environment as follows: