MINERALOGICAL AND GEOCHEMICAL INFLUENCES on THE 2010 NIGERIAN LEAD POISONING OUTBREAK LINKED TO ARTISANAL GOLD ORE PROCESSING

In spring 2010, a pattern of ongoing childhood deaths (160+) and illness (355+ cases) in was noted in several villages of Zamfara State, Nigeria, and was determined to be due to lead poisoning. The presumed cause was artisanal gold ore processing, which had recently expanded and become much more mechanized. In the villages, gold ores are first hand crushed, then pulverized in a flour mill (the recent mechanization), then washed and the gold extracted by amalgamation (liquid mercury intermixed with the ore by hand, then the mixture heated by blowtorch). In late spring, the CDC and ATSDR deployed a rapid response team to help the Nigerian Government and NGOs assess the extent of the lead poisoning, characterize the routes and sources of exposure to lead and other heavy metals, and recommend measures to mitigate exposures. The CDC/ATSDR team collected an extensive sample suite from several affected villages, including raw and ground ores, soils, waters, and sweep dust sweep samples. Neri and others (this meeting) will present an overview of the CDC mission and initial medical findings. The USGS is currently collaborating with CDC to determine mineralogical and geochemical characteristics of the solid samples, to aid in exposure assessment. Preliminary mineralogical analyses indicates that the ore samples processed at Dareta Village are lightly oxidized, and lead sulfide is present in levels ranging from 1 to ~30 vol% in “gold” ore samples to more than 80 vol% in a “lead” ore sample. Lesser amounts of lead sulfate and lead carbonate may also be present. Studies underway include: bulk chemistry to determine concentrations of other potential metal toxicants; X-ray diffraction and scanning electron microscopy to determine mineralogical hosts of metal toxicants; and physiologically based extraction tests on the pulverized ore, soils, and sweep samples to evaluate potential bioaccessibility along ingestion and inhalation exposure pathways. In addition, an experiment with amalgamation of a pulverized gold ore sample will determine if the lead phases present are mercury-soluble, and samples of amalgamation retort gases exhausted through simulated lung fluids will help assess the fate of lead released in to the air by the amalgamation process.