Lead, human exposure

Exposure to lead can occur from a variety of occupational or nonoccupational sources. A comprehensive treatise on human lead exposure is available (3). 

Evans HL New York University Medical Center, New York, NY Behavioral and biochemical markers of human lead exposures (human, rat) National Institute of Environmental Health Sciences... 

Gatsonis CA, Needleman HL. 1992. Recent epidemiologic studies of low-level lead exposure and the IQ of children A meta-analytic review. In Needleman HL, ed. Human lead exposure. Boca Raton, FL CRC Press, 243-255. 

Mushak P. 1993. New directions in the toxicokinetics of human lead exposure. Neurotoxicology 14 29-42. 

Mielke, H.W. Reagan, P.L, 1998. Soil is an important pathway of human lead exposure Environmental Health Perspectives, 106, 217-229. 

Hays SP The role of values in science and policy the case of lead, in Human Lead Exposure. Edited by Needleman HL. Boca Raton, FL, CRC Press, 1992, pp 267-283 Hunt TJ, Hepner R, Seaton KW Childhood lead poisoning and inadequate child care. 

Mushak P (1998) Uses and limits of empirical data in measuring and modeling human lead exposure. 

Cremin, J. D., Jr., M. L. Luck, N. K. Laughlin, and D. R. Smith. 1999. Efficacy of succimer chelation for reducing brain lead in a primate model of human lead exposure. Toxicol. Appl. Pharmacol. 161(3) 283-93. 

The daily average lead intake is about 1 mg, but only about 10% of this reaches to the blood stream. Human food usually contains 0.001-0.025 ppm of lead compounds. Drinks are primarily responsible for most of the human lead exposure old lead pipes, lead containing paint on mugs, and wine or whisky stored in leaded glass, are the main sources. 

Operation of such an interactive, positive feedback cycle for environmental lead, while helpful for effective societal responses to lead s hazards, is nevertheless challenged by some of the environmental and toxicological characteristics of human lead exposures. 

This book is organized into five coherent and interactively related parts containing a total of 29 chapters. Each of the five parts, in turn, is subdivided into chapters that are sequenced to develop topics and their rationales and their contributions to the overall purposes of both the part and the entire book. Parts 1—3 address the science of lead as a pollutant in the human environment and as a potent human toxicant. Part 1 presents multiple chapters on lead in the human environment. Part 2 deals with relevant aspects of defining human lead exposures. Part 3 presents an examination of the nature and extent of human lead toxicity in subsets of the population using criteria for importance and for reliable data availability to inform evaluations done on a body system or organ/organ grouping basis. 

Part 2 consists of four chapters that address the topics associated with human lead exposures. These topics are quantitative in nature, with quantification scaled in terms of amounts, rates, time periods, etc. The chapters appear in the order of their toxicokinetic and toxicological sequences for overall expressions of adverse health risks. 

This chapter provides the connection between the annual and cumulative U.S. and global lead production and consumption figures presented in Chapter 3 and figures in the next two chapters, those for fate and transport of emitted lead through environmental compartments (Chapter 5) and levels of lead in environmental media relevant to human lead exposures (Chapter 6). These three chapters collectively provide a quantitative sense of what amounts of lead entering the broad channels of the U.S. and global commerce have been translated downstream of production or use into levels of lead contamination in the human environment and associated exposures in, at least, the near term. 

Lead contaminates plant crops through surface deposition or root uptake to some extent. Human lead exposures from crops involve direct consumption of food crops by humans or exposure through lead intakes of livestock that become meat sources. 

Leaded dusts can occur in soils, in the household, on hard exterior surfaces such as streets, and as occupational dusts in the specific context noted above. The ability of lead in dusts to rapidly accumulate on hard surfaces produces both a problem for quantification and a potent potential factor in human lead exposure assessments (U.S. EPA, 1986, Ch. 7). The physical and chemical compositions of dusts as well as the levels of lead are determined in large measure by their origin. It is also typical of dusts that they can deposit onto an almost infinite array of hard surfaces, and as a consequence can accumulate to quite high levels over time. This accumulation can be depicted quantitatively as either concentration or as dust lead loadings. 

Davidson, C.I., Rabinowitz, M., 1992. Lead in the environment from sources to human receptors. In Needleman, H.L. (Ed.), Human Lead Exposure. CRC Press, Ann Arbor, MI, pp. 65—86. 

Lead Concentrations in Environmental Media Relevant to Human Lead Exposures... 

For measuring lead in environmental media providing potential human lead exposures, this chapter includes older published data for lead concentrations in media, data which are old enough to encompass the full lifetimes of living populations. This is because of long-term Pb storage in bone. One concern with any appraisal of older lead measurement data in media is that of analytical and statistical data reliability versus that of methods employed with more recent accepted techniques. Sensitivity is of particular concern. A potent toxicant such as environmental lead requires methods for quantification of concentrations of lead at ultra-trace levels in order to permit estimates of the full range of Pb exposures. 

Environmental media of interest in this section on measurement are the same as those producing potential human lead exposures ambient air, lead paints, diet, drinking water, soils and dusts, and some of the more problematic idiosyncratic sources. Sampling and laboratory measurement techniques now widely used are emphasized with comparative statements for older methods provided mainly to offer perspective. Biomarker sampling and measurement methodologies, i.e., procedures for lead in biological media directly relevant to human lead exposures, are presented in a later chapter. 

Ambient air lead partitions into vertical gradients, especially near mobile lead sources, e.g., vehicular exhaust from leaded gasoline combustion. There is special emphasis on those heights above source relevant to human lead exposures. Other specific monitor locating requirements include specifications for distances from roadways (5—100 m) and distances from obstacles between the monitor and the emitting source (Appendix E, CFR, 1982, 40 58). 

There are a variety of field and laboratory analytical methods for soil lead measurement, depending on the type of analysis and its purposes in a given evaluation. Bulk soil lead measurement refers to measurement of the total lead content of the soil sample. Chemical speciation and micromineralogical studies in the context of human lead exposure variability refer to amounts of specific chemical forms of lead and their geochemical states. These studies are sometimes done in tandem with relative bioavailability testings, i.e., amounts of lead being absorbed under in vivo or in vitro simulation of in vivo conditions (Casteel et al., 2006) with respect to Pb source attribution. Stable isotopic analysis studies deal with the quantitative stratification of lead s stable isotopic composition into the four main stable isotopes lead-204, lead-206, lead-207, and lead-208 (Gulson et al., 1995, 1997). 

Concentrations of lead in the various environmental media described in this section are presented for extended periods. The available data that meet minimal statistical and measurement criteria generally only extend from the late 1960s/early 1970s to the present. The purposes of a wide temporal look at environmental lead concentrations are several. First, the nature of lead as an accumulating contaminant in the bodies of human populations requires an appreciation of the amounts of environmental lead that existed in past decades. As noted earlier, lead levels in media have been changing, mainly downward, so that current human body lead burdens are only partially quantifiable from current lead intakes into body compartments. Secondly, the use of predictive, biokinetic models of human lead exposures for simulating Ufe-time lead exposures requires knowledge of lead intakes from the earliest periods of life. 

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