Urinary non-precipitable lead in lead workers

Abstract

Sixty-six workers engaged in lead-glazing pottery with a presumed moderate exposure to lead were studied. The group comprised 20 men with long-term exposure to lead and positive laboratory signs of increased lead absorption (Group A); 22 with long-term exposure and negative laboratory signs (Group B); 11 with short-term exposure and positive laboratory signs (Group C); and 13 with short-term exposure and negative laboratory signs (Group D). In addition, 14 workers employed in casting the kelmet alloys with presumed heavy exposure to lead (Group E) and seven healthy individuals (Group F) were included. Urine samples from all the subjects were analysed to determine, first, the total lead using the ashing technique, and then the precipitable lead using the coprecipitation technique of Cholak, Hubbard, and Burkey (1948), but modified slightly by us. Thus, the non-precipitable lead fraction in urine was the difference between the two measurements and this was also expressed as a percentage of the total lead. The mean total lead and the mean proportion of non-precipitable lead were 0.62 mumol/l and 48.7%, 0.35 mumol/l and 44.9%, 0.40 mumol/l and 48.9%, 0.17 mumol/l and 24.6%, 1.43 mumol/l and 44.3%, 0.14 mumol/l and 18.8% for Groups A, B, C, D, E, and F respectively, showing that a large part of urinary lead was eliminated as precipitable lead in Groups D and F who had normal lead excretion, while about half was eliminated as non-precipitable lead in the other four groups who had excessive lead excretion. No essential difference in the proportion of non-precipitable lead among Groups A, B and C excluded the possibility that the proportion might be directly related to the period of exposure to lead and to the laboratory findings of excessive lead absorption. The mean proportion of non-precipitable lead for the physiological (up to 0.240 mumol/l), intermediate (0.241 to 0.721 mumol/l), and excessive (above 0.722 mumol/l) total lead levels was 26.7, 41.3, and 52.3% respectively, in the lead workers comprising Groups A, B, C, and E each showing increased lead excretion when grouped together. these data suggested that, when urinary lead is within the normal range, it is excreted largely as precipitable lead even in individuals exposed to lead, and that the principal conditions determining the excretion of non-precipitable lead would be the current or recent degree of lead absorption. The excretory mechanisms and the biological significance of the non-precipitable lead are also discussed.