Absorption - Pesticide Biotransformation and Disposition - page 25

Dermal

iv, ip, sc, im Inhalation

Oral

Gastrointestinal
tract

Skin Lung

Excretion Excretion

Liver Blood

Metabolites

Target
organ(s)

Kidney

Excretion

Figure 3.1 Representation of the absorption, distribution, metabolism, and excretion of toxicants.

excretion are discussed in detail in other chapters of this work. This chapter focuses on
pesticide absorption with an expanded focus on dermal absorption, as workers involved
in pesticide manufacturing, formulation, or application and harvesting of treated crops
are more likely to be exposed to these chemicals via the skin.

FACTORS THAT INFLUENCE THE TRANSFER AND AVAILABILITY OF
CHEMICALS IN THE BODY

For the routes of pesticide exposure relevant to humans, the pesticide must cross one
or more cell membranes to reach the bloodstream, and then one or more additional
cell membranes to leave the blood and enter tissues. The following discussion concerns
the factors that influence the transfer of chemicals across biological membranes.

Properties of Cell Membranes
Cell membranes (i.e., plasma membranes) consist of phospholipids and proteins
( Figure 3.2 ). The fluid and dynamic phospholipid bilayer, with polar head groups
on the intracellular and extracellular surfaces and fatty acid chains filling the inner
space, acts as a permeability barrier to water-soluble molecules. Proteins interspersed
throughout the phospholipid bilayer mediate the transport of small, water-soluble mol-
ecules into and out of the cell by forming pores or by acting as carriers. Molecules