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Abstract
In an attempt to determine whether current levels of lead in the environment are causing any progressive change in the blood and urine lead concentrations of the US population, an investigation was undertaken to monitor, for a five-year period, urine and blood lead values of a population living in 23 US cities. Urine specimens were obtained annually during 1967 through 1971 from approximately 6,000 subjects while blood specimens were obtained from 10% to 20% of these same individuals. Determinations of lead levels in these specimens indicated that blood lead did not increase and urine lead decreased during the study. Analysis of quality control data, selection of data for statistical treatment, and seasonal effects did not explain the downward trend in urine lead levels.