Abstract

To assist in recommendations for the most suitable lead abatement policies in Broken Hill, New South Wales, Australia, knowledge of the sources and pathways of the lead into humans is critical. We have approached these problems using the lead isotope fingerprinting method, combined with mineral speciation and "bioavailability" tests, approaches which have in the past been largely applied to mineral exploration.High precision lead isotope ratio measurements and lead contents were determined by thermal ionization mass spectrometry on biological samples (blood, urine) and environmental samples from 27 families, encompassing 60 children, 41 female adults, and 17 male adults. Environmental samples analyzed (not from every household) included soils, gutter sweepings, ceiling dust, vacuum cleaner dust, long-term dust, surface dust wipes, external and internal air, food, water, and gasoline.Sources of lead have been identified in the blood of children, using lead isotopes, with dominant contributions from the Broken Hill orebody, but with individual cases having a dominant source of lead from gasoline or paint. Nevertheless, of 28 children with a blood lead level (Pb B ) > 15 mu /dl, approximately 30 percent have more than 50 percent of their Pb B from sources other than orebody lead. Female adults generally have a low Pb B , <10 mu /dl, and the source of their lead is attributed to air (gasoline, orebody), food, and water. The source of lead in male adults can usually be correlated with their occupation, depending on whether it is related to high risk activities, such as mining (dominantly orebody lead) or service stations (gasoline lead), or "nonexposed." Knowledge of the occupation and lead isotope composition in the father's blood is an important indicator of lead pathways. Other potential sources of lead, such as food and water, have lead contents too low to be significant contributors to lead levels in most children.Scanning electron microscopy (energy dispersive X-ray analyses) identified the most common lead species in soils and dusts to be composed of a complex Pb,Fe,Mn,Ca,Al,Si,O material with rare galena in houses close to the central mining activity. These lead complexes are quite different 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 quartz. Approximations of bioavailability (more correctly, solubility) were made by leaching, with 0.1M HCl for 2 hr at 37 degrees C, bulk (unsized) and a critical size fraction of -53+38 mu m. The 0.1M HCl extracts 33 to 61 percent (mean = 47 + or - 10%, n = 7) of the total leachable lead from gutter sweepings, from 41 to 84 percent (mean = 60 + or - 10%, n = 10) from soils, and 17 to >100 percent (mean = 47 + or - 38%, n = 5) from vacuum cleaner dusts. Thus the currently suggested amounts of approximately 100 mg/d ingested soil (dirt) and dust for a Broken Hill child can readily account for the elevated lead levels compared with the amounts for children in many other mining communities. Based on these investigations it is possible to construct a flow sheet of sources and pathways for the lead into humans at Broken Hill on which to base correct remedial actions.

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