ISOTOPIC-RATIOS OF LEAD IN HUMAN TEETH AND SOURCES OF EXPOSURE IN EDINBURGH

The mean Pb-206/Pb-207 ratio of 1.131 +/- 0.015 (range 1.112-1.150) found for lead in the teeth of 'low-lead exposure' children in Edinburgh is intermediate between the observed ratios for leaded petrol (1.075 +/- 0.013) and tap water in contact with lead pipes (1.160 +/- 0.012) and comparable with that reported for food in the UK. Quantitative source apportionment on the basis of one lead isotopic ratio, however, may well be hindered by the wide range of Pb-206/Pb-207 values (1.098-1.183; mean 1.142 +/- 0.031) found for old, high-lead (> 1.0%) paint and the similarity of the mean ratio (1.159 +/- 0.011) for high-lead (> 0.1%) dust in older houses to that for tap water. The potential benefit of using more than one stable lead isotopic ratio in such investigations is endorsed by the identification of two distinct groups of children close to the excellent best-fit line (r = -0.976) through the Pb-208/Pb-206 versus Pb-206/Pb-207 plot for the extensive series of environmental (petrol, atmospheric particulates, street dust, paint (< 1.0%), house dust, tap water) data, while the samples of high-lead (> 1.0%) paint all lie clearly to one side of the line, and by the differences sometimes observed between the enamel and dentine fractions of individual adult teeth for the Pb-208/Pb-206 and Pb-208/Pb-207, but not Pb-206/Pb-207, ratios.