Effect of smelter emission reductions on children's blood lead levels.

Trail, British Columbia has been the site of an active lead-zinc smelter for approximately 95 years. Since 1989, the community has been monitoring blood lead levels in children, studying exposure pathways and conducting comprehensive education and case management programs. From 1989 through 1996, mean blood lead levels of pre-school children declined at an average rate of 0.6 microg/dl per year. From 1996 to 1999, mean blood lead levels fell at an average rate of 1.8 microg/dl per year, from 11.5 in 1996 to 5.9 in 1999. The recent rapid decline appears to be mainly attributable to the start-up of a new lead smelter using modern flash-smelting technology in May of 1997. In 1998, the annual arithmetic mean air lead level in Trail was 0.28 microg/m(3), compared with 1.1 microg/m(3) in 1996. Reductions of approximately 50% were observed in lead loadings and concentrations in outdoor dustfall, street dust and indoor dustfall after smelter emissions were reduced. Slight reductions (statistically insignificant) have been observed in carpet dust and soil lead concentrations. During the summer of 2001, the smelting and refining operations at Trail were shut down completely for 3 months. During this period, average air lead levels in Trail dropped to 0.03 microg/m(3). The average blood lead level in Trail pre-school children at the end of the shutdown was 4.7 microg/dl. These results challenge prevailing theories about the relative importance of various environmental lead sources. For example, the US EPA Integrated Biokinetic Uptake Model for Lead (IEUBK), with its emphasis on soil concentrations, would not have predicted the dramatic decline in children's blood lead levels seen in Trail following the reductions in air lead levels. The Trail experience suggests that increased attention should be paid to the importance of active sources of highly bioavailable and mobile lead bearing dusts.