Distribution and Pharmacokinetics Models - Pesticide Biotransformation and Disposition - page 144

In addition to metabolism, chemicals may be eliminated from the body by excre-
tion in urine, exhaled air, and other routes that are not discussed here (e.g., sweat, bile,
and milk). A typical equation for the concentration of chemical in exhaled air is:

C
P

a

C 0 7 . 0 3 . C .

= + (75)

ex 1

b

Equation (69) uses the assumption that exhaled air is a mixture of inhaled air (30%)
and expired alveolar air (70%). Urinary excretion may be described in a number of
ways, including excretion by first-order and saturable processes similar to the descrip-
tions of metabolism in Eqs. (69) and (70). The same is true for elimination by other
routes.

CONCLUSIONS

To either exert a deleterious effect or be detoxified, xenobiotics, including pesticides,
must be absorbed, distributed, and/or metabolized; react with a macromolecule or
other receptor; and/or be excreted. Distribution and pharmacokinetics are the sub-
jects of this chapter. In the case of toxicants such as pesticides, the term toxicokinet-
ics is frequently used. Noncompartmental, compartmental, and physiological models
were considered in this chapter including the quantitative methodology for utilizing
these models. The mechanisms of absorption and transport, metabolism, mode of toxic
action, and excretion are considered elsewhere in this handbook.

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