SOURCE APPORTIONMENT OF LEAD IN FUGITIVE DUSTS FROM UNSURFACED ROADS IN SOUTHEAST, MO

The isotopic composition of Pb in fugitive dust generated by a vehicle driving on 17 unsurfaced roads in Missouri was measured to identify sources of Pb in resuspended dust from unsurfaced mining area roads. A three isotope plot for high precision analyses of ²⁰⁸Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb indicated that the fugitive dust samples plot on the mixing line of previously published data for Viburnum Trend (VT) ores and background soils. Two end-members were selected to apportion Pb in samples according to contributions from a homogenous VT ore source and a heterogeneous background source consisting of a mixture of several Pb types that cannot be delineated with confidence using existing data. The background end-member assumed a mixture of Pb isotopes that represent natural Pb derived from bedrock and contributions from regional aerosol deposition as well as local deposition from varied sources. A simple two component mixing model applied to ²⁰⁷Pb/²⁰⁶Pb of partially digested samples showed mining roads apportion between 22 and 49% of Pb from VT ore, and 51 to 78% from background. Labile forms of Pb as determined through sequential extraction had an overall smaller contribution from VT ore (35%) suggesting Pb-types associated with the background end-member are more problematic to human and environmental health. To achieve better resolution in our source apportionment investigation, additional samples are being analyzed to refine end-member accounting. These samples include top of bedrock, unconsolidated overburden, mine tailings, and quarry stone applied to unsurfaced roads throughout the region.