Human oral and inhalation exposures to lead: Summary of Kehoe balance experiments

Abstract

The Kehoe Pb balance experiments were carried out from 1937-1972 and involved over 21,000 days of measured exposure of Pb in humans. Pb balance and Pb in the diet, feces, urine and blood were measured under normal conditions and during periods of oral and airborne Pb supplementation. Considerable natural variability was seen, due primarily to variations in dietary Pb. The overall mean blood Pb concentration for all subjects was 25 .mu.g/100 g, with individual control means ranging from 18-40 .mu.g/100 g. Urinary Pb averaged 29 .mu.g/l overall, with individual control means ranging from 19-45 .mu.g/l. The overall average diet contained 181 .mu.g/day (159 .mu.g/day based on median data); the mean dietary Pb for the individual control periods decreased from .apprx. 300 .mu.g/day in 1937 to 100 .mu.g/day in 1970. Fecal Pb had an overall mean of 225 .mu.g/day (212 .mu.g/day based on median data) on a per sample basis, which exceeded the dietary Pb average because most subjects did not defecate daily. Averaged over the entire control period, fecal Pb was 196 .mu.g/day, still in excess of the overall average diet. Pb balance was calculated as dietary Pb minus Pb in the feces and urine, and did not include an estimate of inhaled Pb. Although 3 subjects were in positive balance during their control periods, the overall average balance was -32 .mu.g/day, ranging from -106 to +25 .mu.g/day for individual control periods. An appreciable amount of Pb adsorbed from the air was excreted. Ingestion experiments involved daily supplements of 300, 1000, 2000 and 3000 .mu.g Pb/day. Except for subject SW, who received the 300 .mu.g supplementation, all subjects experienced increased Pb in the blood, urine, feces and body burden proportional to ingested Pb. For SW, blood and urine Pb did not increase even though body and fecal Pb did. The feces, blood, urine and balance increased by 0.83 .mu.g/day, 0.017 .mu.g/100 g, 0.045 .mu.g/day and 0.133 .mu.g/day for each increase of 1 .mu.g Pb in the diet. Inhalation exposure experiments involved chamber concentrations of 10, 20, 75 and 150 .mu.g/m3 for varying exposure times. Overall chamber exposure rates ranged from 0.6-35.9 .mu.g/m3, averaged over the entire exposure period. The influence of natural variability of dietary Pb permeated all inhalation experimental periods and overrode the responses of blood, urinary and fecal Pb at adjusted exposure rates < 10 .mu.g/m3 (< chamber concentrations of 75 .mu.g/m3). The blood, urine and feces increased by 0.57 .mu.g/100 g, 1.41 .mu.g/day and 1.47 .mu.g/day for each increase of 1 .mu.g/m3 Pb in the air. All subjects who experienced obvious increases in body Pb during exposure periods showed obvious and prompt body Pb washout during post-exposure periods.