Metabolism and toxicity of lead in children and adults

Abstract

Lead does not participate in any metabolic process in humans. Nevertheless, it is the most important non ferrous metal in industry since ancient times. This fact promoted a huge and extensive environmental contamination, allowing for an excessive input of lead by humans through ingestion and inhalation. In this review it is discussed aspects of kinetics and toxicity of lead in its inorganic form, being the most important chemical form presenting in occupational and general environment. As a metal, lead does not suffer biotransformation as other toxic substances. Its metabolism is limited to a complex kinetics of distribution and excretion which depends on its chemical speciation, determining the redox potential, rates of ionization and protein binding; crossing of blood brain and placental barriers; rates of tissue accumulation and renal excretion. Adults absorb 10% after lead ingestion, contrasting with children that can absorb 50%. Lead is distributed rapidly and easily through all tissues, including brain, crossing placental barrier and being secreted in maternal milk. Elimination half lifes can be very different according to the body compartment as follows: for blood = 15 to 30 days (in children under low doses of exposure = 10 to 12 months); soft tissues in general = 60 days; trabecular bone = 90 to 120 days; cortical bone with stable deposits = 25 to 30 years. Lead presents toxic action in the central and peripheral nervous system, renal and hemopoietic systems, by toxic mechanisms that are discussed in the paper.