ABSTRACT
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is dependent upon the disposition of these materials within the respiratory system. This, in turn, depends upon their patterns of deposition (the sites within which they initially come into contact with airway epithelial surfaces and the amounts removed from the inhaled air at these sites), any metabolism, and their clearance (the rates and routes by which dissolved gases or deposited particles are physically removed from the respiratory tract). For chemicals that exert their action upon surface contact, the initial deposition is a predictor of toxic response. In many other cases, however, it is the net result of deposition and clearance (namely, retention, or the amount of material remaining in the respiratory tract at specific times after exposure) that influences toxicity. This chapter provides information on the deposition of inhaled particles and gases, the metabolism of deposited materials by the respiratory tract, clearance mechanisms and rates, and ultimate retention patterns.
