Temporal Aspects of Risk Characterization of Lead

Abstract

Temporal factors are an integral part of the components of the risk assessment: hazard identification, dose-response assessment, and exposure estimation. Critical elements of risk characterization include expressions of uncertainty and variability in the data base describing toxicity, dose-response, and exposures to lead. Over the past two decades our understanding of the mechanism(s) of action of lead has resulted in progressively lower quantities of lead being of concern. An increased level of certainty has developed over the past ten years on the nature of the adverse neurodevelopmental consequences of lead exposure. Dose-response evaluation and accompanying risk characterization have been expressed by a number of organizations (e.g., a series of statements by public health authorities describing tolerable blood lead concentrations for children and adults, which have been lowered over time). Blood lead concentrations of concern for young children have decreased over time from ≥ 40 μgldL to ≥ 10 μgldL. Expression of the hazard of lead to the nervous system is dependent upon the developmental period in which lead exposure occurs. Based on available data, lead exposures in utero are considered a far greater hazard to the nervous system than are lead exposures that occur later in development. Over the past two decades lead exposures have decreased markedly, reflecting virtual elimination of lead solder from food processing and phase-out of leaded fuel additives from gasoline. Lead-based paints in housing remain the major source of lead for young children in the United States. Greater clarification of the time period needed to assess lead exposures associated with adverse neurobehavioral effects is a current goal of risk characterization.