Appendix A: Dose and Exposure Characterizations


Systemic, oral, intravenous, and intraperitoneal exposures are commonly expressed in terms of the weight of the agent (milligrams or micrograms) per kilogram of the weight of the organism dosed.


Cutaneous exposures may be expressed in terms of a total dose or in terms of the weight of the agent (milligrams or micrograms) per square centimeter times the total area exposed.

The lethal dose (LD) for the organism in question is expressed in one of two ways:

Incapacitation can vary from moderate (unable to see, breathless) to severe (convulsions).


Respiratory exposures are expressed in terms of the product of the concentration (C) of the vapor or aerosol, usually expressed as milligrams (or micrograms) per cubic meter (or liter), e.g., 35 mg-min/m3 or 0.13 µg-min/l, and the length of the exposure (T). The resulting value is known as the CT.

Note that CT is an expression of exposure, not the amount inhaled or deposited. The same CT can be produced by varying concentration or exposure time. The effect of a given CT may or may not be the same if T is varied from a few minutes to several hours. For example, a CT of 5 can be obtained by exposure to 0.05 mg/m3 for 100 minutes or to 5 mg/m3 for 1 minute. The generalization is not reliable for very short exposures (during which breath might be held) or very long exposures (during which metabolic detoxification may operate).

As above, certain key dosages are of interest[1]:

[1]These definitions are also used for vapor or aerosol effects on the skin.

Previous Chapter
Appendix B