tract. Some chemicals increase intestinal permeability and thus increase the rate of absorption. More chemical will be absorbed if the chemical remains in the intestine for a long time. If a chemical is in a relatively insoluble, solid form, it will have limited contact with gastrointestinal tissue, and its rate of absorption will be low. If it is an organic acid or base, it will be absorbed in that part of the gastrointestinal tract where it is most fat-soluble. Fat-soluble chemicals are absorbed more rapidly and extensively than water-soluble chemicals.
Exposure to toxic chemicals by injection does not occur frequently in the chemical laboratory. However, it can occur inadvertently through mechanical injury from "sharps" such as glass or metal contaminated with chemicals or when chemicals are handled with syringes. The intravenous route of administration is especially dangerous because it introduces the toxicant directly into the bloodstream, eliminating the process of absorption. Nonlaboratory personnel, such as custodial workers or waste handlers, must be protected from this form of exposure by putting all "sharps" in special trash containers and never in the ordinary scrap baskets. Hypodermic needles with blunt ends are available for laboratory use.
Exposure to a harmful chemical can result in local toxic effects, systemic toxic effects, or both. Local effects involve injury at the site of first contact. The eyes, the skin, the nose and lungs, and the digestive tract are typical sites of local reactions. Examples of local effects include (1) ingestion of caustic substances causing burns and ulcers in the mouth, esophagus, stomach, and intestines, (2) inhalation of hazardous materials causing toxic effects in the nose and lungs, and (3) contact with harmful materials on the skin or eyes leading to effects ranging from mild irritation to severe tissue damage. Systemic effects, by contrast, occur after the toxicant has been absorbed from the site of contact into the bloodstream and distributed throughout the body. While some chemicals produce adverse effects on all tissues of the body, other chemicals tend to selectively injure a particular tissue or organ without affecting others. The affected organs (e.g., liver, lungs, kidney, central nervous system) are referred to as the target organs of toxicity. The target organ of toxicity is not necessarily the organ where the highest concentration of the chemical is achieved. Hundreds of different systemic toxic effects of chemicals are known. Systemic effects can result from single (acute) exposures or from repeated or long-duration (chronic) exposures, becoming evident only after a long latency period.
Toxic effects can be further classified as reversible or irreversible. Reversible toxicity is possible because in some cases tissues have the capacity to repair toxic damage, so that the damage disappears following cessation of exposure. Irreversible damage, in contrast, persists even after cessation of exposure. Recovery from a burn is a good example of reversible toxicity; cancer is generally thought to be irreversible.
The chemicals used in the laboratory can be grouped among several different classes of toxic substances. Many chemicals display more than one type of toxicity. The following are the most common classes of toxic substances encountered in laboratories.
Irritants are noncorrosive chemicals that cause reversible inflammatory effects (swelling and redness) on living tissue by chemical action at the site of contact. A wide variety of organic and inorganic chemicals are irritants, and consequently, skin and eye contact with all chemicals in the laboratory should be avoided.
Corrosive substances cause destruction of living tissue by chemical action at the site of contact and can be solids, liquids, or gases. Corrosive effects can occur not only on the skin and eyes, but also in the respiratory tract and, in the case of ingestion, in the gastrointestinal tract as well. Corrosive materials are probably the most common toxic substances encountered in the laboratory. Corrosive liquids are especially dangerous because their effect on tissue generally takes place very rapidly. Bromine, sulfuric acid, aqueous sodium hydroxide solution, and hydrogen peroxide are examples of highly corrosive liquids. Corrosive gases are also frequently encountered. Gases such as chlorine, ammonia, and nitrogen dioxide can damage the lining of the lungs, leading, after a delay of several hours, to the fatal buildup of fluid known as pulmonary edema. Finally, a number of solid chemicals have corrosive effects on living tissue. Examples of common corrosive solids include sodium hydroxide, phosphorus, and phenol. Dust from corrosive solids can be inhaled and cause serious damage to the respiratory tract.
There are several major classes of corrosive substances. Strong acids such as nitric, sulfuric, and hydrochloric acid can cause serious damage to the skin and eyes. Hydrofluoric acid is particularly dangerous and