Absorption - Pesticide Biotransformation and Disposition - page 24

3

CHAPTER

Absorption

Ronald E. Baynes, Jim E. Riviere
North Carolina State University, Raleigh, NC, USA

Outline
Introduction 25

Factors that Influence the Transfer and Availability of Chemicals in the Body 26

Properties of Cell Membranes 26

Transport Mechanisms 27

Passive Transport 27

Specialized Transport 29

Protein (Macromolecular) Binding 30

Absorption 31

Percutaneous Absorption 33

Anatomical Site Differences 33

Pesticide Formulation and Mixtures 34

Environmental Factors 37

Absorption from the Gastrointestinal Tract 42

Absorption from the Respiratory Tract 44

Absorption after Exposure by Other Routes 45

Summary and Future Directions 46

References 47

INTRODUCTION
For a pesticide to elicit toxicity, it must be transferred from the external site of exposure
to the target site (e.g., organ, nucleic acid, receptor) and achieve a sufficiently high con-
centration in the target organ ( Figure 3.1 ). Absorption is the translocation of the pes-
ticide from an external source of exposure to the bloodstream. Once in the blood, the
chemical is distributed through the body and delivered to tissues, where it may leave
the blood and enter the cells of the tissue or it may remain in the blood and simply pass
through the tissue. In certain tissues such as the liver, the chemical may be effectively
removed from the body by metabolism. Other tissues, such as kidney and lung, serve to
eliminate xenobiotics from the body by excretion. Absorption, distribution, metabolism,
and excretion, which are collectively termed disposition, are all factors that affect the
concentration of a chemical in target tissues. Pharmacokinetics refers to the mathemati-
cal description of the time course of chemical disposition in the body. Metabolism and