SOURCE AND PATHWAYS OF LEAD IN HUMANS FROM THE BROKEN-HILL MINING COMMUNITY - AN ALTERNATIVE USE OF EXPLORATION METHODS

To assist in recommendations for the most suitable lead abatement poli cies in Broken Hill, New South Wales, Australia, knowledge of the sour ces and pathways of the lead into humans is critical. We have approach ed these problems using the lead isotope fingerprinting method, combin ed with mineral speciation and ''bioavailability'' tests, approaches w hich have in the past been largely applied to mineral exploration. Hig h precision lead isotope ratio measurements and lead contents were det ermined by thermal ionization mass spectrometry on biological samples (blood, urine) and environmental samples from 27 families, encompassin g 60 children, 41 female adults, and 17 male adults. Environmental sam ples analyzed (not from every household) included soils, gutter sweepi ngs, ceiling dust, vacuum cleaner dust, long-term dust, surface dust w ipes, external and internal air, food, water, and gasoline. Sources of lead have been identified in the blood of children, using lead isotop es, with dominant contributions from the Broken Hill orebody, but with individual cases having a dominant source of lead from gasoline or pa int. Nevertheless, of 28 children with a blood lead level (Pb(B)) > 15 mug/dl, approximately 30 percent have more than 50 percent of their P b(B) from sources other than orebody lead. Female adults generally hav e a low Pb(B), <10 mug/dl, and the source of their lead is attributed to air (gasoline, orebody), food, and water. The source of lead in mal e adults can usually be correlated with their occupation, depending on whether it is related to high risk activities, such as mining (domina ntly orebody lead) or service stations (gasoline lead), or ''nonexpose d.'' Knowledge of the occupation and lead isotope composition in the f ather's blood is an important indicator of lead pathways. Other potent ial sources of lead, such as food and water, have lead contents too lo w to be significant contributors to lead levels in most children. Scan ning electron microscopy (energy dispersive X-ray analyses) identified the most common lead species in soils and dusts to be composed of a c omplex Pb,Fe,Mn,Ca,Al,Si,O material with rare galena in houses close t o the central mining activity. These lead complexes are quite differen t from ones found in other mining communities, such as those found in the United States, where the lead may be in less soluble forms such as pyromorphite or encapsulated in less soluble anglesite, pyrite, or qu artz. Approximations of bioavailability (more correctly, solubility) w ere made by leaching, with 0.1 M HCl for 2 hr at 37-degrees-C, bulk (u nsized) and a critical size fraction of -53 + 38 mum. The 0.1 M HCl ex tracts 33 to 61 percent (mean = 47 +/- 10%, n = 7) of the total leacha ble lead from gutter sweepings, from 41 to 84 percent (mean = 60 +/- 1 0%, n = 10) from soils, and 17 to > 100 percent (mean = 47 +/- 38%, n = 5) from vacuum cleaner dusts. Thus the currently suggested amounts o f approximately 100 mg/d ingested soil (dirt) and dust for a Broken Hi ll child can readily account for the elevated lead levels compared wit h the amounts for children in many other mining communities. Based on these investigations it is possible to construct a flow sheet of sourc es and pathways for the lead into humans at Broken Hill on which to ba se correct remedial actions.