Blood-lead level (Pb-B), erythrocyte delta-aminolevulinic acid dehydratase (ALAD) activity, free erythrocyte porphyrin (FEP) concentration, delta-aminolevulinic acid concentration in urine (ALAU), hematocrit value, and hemoglobin concentration were compared for groups of children 10-13 years old from areas differently polluted by lead (rural area and lead smelter area). The biological responses of the children were also compared with those observed in adults similarly exposed to lead (Pb-B: 10-40 mug/100 ml). Compared with the rural children, children living less than 1 km from the smelter exhibited a significant increase of Pb-B and FEP, a significant inhibition of ALAD, and a slight positive correlation of ALAU with Pb-B; however, they showed no biological signs of anemia. In children living approximately 1.5 km from the smelter, there was still a significant increase of Pb-B and a concomitant inhibition of ALAD, but no change in FEP concentration. Comparison of the dose-response curves between Pb-B and FEP in adult males, adult females, and children indicates that the sensitivity to lead is in the order of children larger than or equal to women greater than men. Based on the FEP response, it is proposed that 25 mug Pb/100 ml blood be regarded as the maximum biologically allowable concentration of lead in blood of school-age children.
This is a follow-up study of UNEP/WHO Pilot Project on Assessment of Human Exposure to Lead and Cadmium through Biological Monitoring, carried out in 1983/1984. The main objectives of the follow-up study were: to study whether differences in blood-lead levels found between countries in the Biological Monitoring Project were confirmed and were primarily due to exposure via ingested lead (oral intake) or via inhaled lead; to make a preliminary survey, in selected areas, of the possible sources of high exposure (Malta, Belgium). Four countries participated: Belgium, Malta, Mexico, Sweden. To insure comparability between the populations, certain categories were monitored: teachers for socio-economic status, non smoking males, aged between 25 and 50 years old. The blood-lead concentration (PbB) was measured to determine the current exposure and the feces-lead excretion (PbF) was determined to find out the part of the exposure due to ingestion. Blood-lead levels and feces-lead excretion were very different between the four countries. Median values for PbB, in micrograms Pb/1, were, in decreasing values 247 in Malta, 188 in Mexico, 135 in Belgium and 53 in Sweden. Median values for PbF, in micrograms Pb/day, were 361 in Malta, 159 in Mexico, 82 in Belgium and 22 in Sweden. Oral intake seems to be the major exposure route in the four countries. The relationship between PbB and PbF is curvilinear. To investigate the possible source of high exposure, a preliminary survey was made in Malta and Belgium; lead in air suspended and sedimenting particles was monitored as well as the lead concentration in some food and street dust samples. Concerning the comparison of lead concentrations in these environmental samples between Belgium and Malta, no major differences were detected. The high internal exposure to lead in Maltese people, as measured by PbB, is probably due to a combination of several factors.
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