LEAD POISONING AND MEDICAL GEOLOGY: AN UNFINISHED STORY

The awareness of the severe neurotoxicity of lead in humans has provoked a number of regulatory measures, including phase-out of lead as additives to gasoline, paint, water pipes and solder, which significantly reduced the human exposure to lead. The end-product of these actions? A reduction in lead poisoning of children from ~88% of the national population in the 1970s to less than 2% at present. By all usual accounts, these facts imply a seamless and uniform industrial and governmental response to this threat. Why then are high blood lead levels, a sure sign of lead intake and a grim warning of retardation, still seen in many urban youth populations? Recent work indicates that although point sources have been largely removed, diffuse soil lead from 100 years of anthropogenic activities continues to poison urban youth, particularly minority populations and those from low socio-economic status households.

To begin addressing the question of lead sources and sinks, and potential remediation, we focused on Indianapolis, a large mid-western city which exhibits clusters of high blood-lead levels in children and has excellent records of traffic volumes, housing development, blood lead testing, and atmospheric parameters. We collected and analyzed surface soil samples, and examined temporal trends in atmospheric particulate loads, precipitation, and blood lead levels in children. We found several interesting features: 1) lead concentrations typically ranged from 50 - 300 ug/g, and 2) lead decreased exponentially away from roads, often decreasing from ~400 ug/g to background values of 50 ug/g at a distance of 50 m from a road, with a high dependence on past traffic volume. A comparison to health records of blood lead levels shows correlation between high soil lead and high blood lead levels. The regional characteristics of the high soil lead values indicate airborne rather than point sources of lead to these areas. Intriguingly, the atmospheric records of particulate load and precipitation correlate extremely well with children’s blood lead levels; the relationship between drier conditions and high levels of small particulate loading can be modeled and used to predict seasonal changes in children’s blood lead levels.