Office of Research

A. Routes of Exposure


Exposure to chemicals may occur by the following routes:

1.         inhalation,

2.         ingestion,

3.         contact with skin and eyes, or

4.         injection.



Inhalation of toxic vapors, mists, gases, or dusts can produce poisoning by absorption through the mucous membrane of the mouth, throat, and lungs and can seriously damage these tissues by local action. Inhaled gases or vapors may pass rapidly into the capillaries of the lungs and be carried into the circulatory system.  This absorption can be extremely rapid. The rate will vary with the concentration of the toxic substance, its solubility in tissue fluids, the depth of respiration, and the amount of blood circulation, which means that it will be much higher when the person is active than when he or she is at rest.

The degree of injury resulting from exposure to toxic vapors, mists, gases, and dusts depends on the toxicity of the material and its solubility in tissue fluids, as well as on its concentration and the duration of exposure. Chemical activity and the time of response after exposure are not necessarily a measure of the degree of toxicity. Several chemicals (e.g., mercury and its derivatives) and some of the common solvents (benzene) are cumulative poisons that can produce body damage through exposure to small concentrations over a long period of time.



Many of the chemicals used in the laboratory are extremely dangerous if they enter the mouth and are swallowed.

The relative acute toxicity of a chemical can be evaluated by determining its LD50, which is defined as the quantity of material that, when ingested or applied to the skin in a single dose, will cause the death of 50% of the test animals. It is expressed in grams or milligrams per kilogram of body weight. In addition, many chemicals may damage the tissues of the mouth, nose, throat, lungs, and gastrointestinal tract and produce systemic poisoning if absorbed through the tissues.

To prevent entry of toxic chemicals into the mouth, laboratory workers will wash their hands before eating, smoking, or applying cosmetics; immediately after use of any toxic substance; and before leaving the laboratory. Food and drink may not be stored or consumed in areas where hazardous chemicals, radioactive materials, or biohazardous materials are being used. Chemicals should never be tasted; and pipetting and siphoning of liquids should never be done by mouth.



Contact with the skin is a frequent mode of chemical injury. A common result of skin contact is a localized irritation, but an appreciable number of materials are absorbed through the skin with sufficient rapidity to produce systemic poisoning. The main portals of entry for chemicals through the skin are the hair follicles, sebaceous glands, sweat glands, and cuts or abrasions of the outer layers of the skin. The follicles and glands are abundantly supplied with blood vessels, which facilitates the absorption of chemicals into the body.

Contact of chemicals with the eyes is of particular concern because these organs are so sensitive to irritants. Few substances are innocuous in contact with the eyes; most are painful and irritating, and a considerable number are capable of causing burns and loss of vision. Alkaline materials, phenols, and strong acids are particularly corrosive and can cause permanent loss of vision. Also, eyes are very vascular and provide for rapid absorption of many chemicals.

Skin and eye contact with chemicals should be avoided by use of appropriate protective equipment.

In the event of skin contact, the affected areas should be flushed with water and medical attention should be sought if symptoms persist; in the event of eye contact, the eye(s) should be flushed with water for 15 min and medical attention should be sought whether or not symptoms persist.



Exposure to toxic chemicals by injection seldom occurs in the chemical laboratory. However, it can inadvertently occur through mechanical injury from glass or metal contaminated with chemicals or when chemicals are handled in syringes.


B.        Laboratory Specific Operating Procedures

Place laboratory specific operating procedures for working with particularly hazardous substances, here. (See Appendix J for guidelines on developing SOPs)