Isotopically constrained lead sources in fugitive dust from unsurfaced roads in the southeast Missouri mining district * Emitt C. Witt III a, b, * , Michael J. Pribil c , John P. Hogan b , David J. Wronkiewicz b, d a U.S. Geological Survey, Center of Excellence for Geospatial Information Science, Rolla, MO 65409, USA b Missouri University of Science & Technology, Department of Geologic Sciences and Engineering, Rolla, MO 65409, USA c U.S. Geological Survey, Central Mineral and Environmental Resources Science Center, USA d Missouri University of Science & Technology, Environmental Research Center for Emerging Contaminants, Rolla, MO 65409, USA article info Article history: Received 21 March 2016 Received in revised form 20 May 2016 Accepted 25 May 2016 Available online xxx Keywords: Road dust Pb isotopic ratios Pb apportionment Unsurfaced roads Sequential extraction abstract The isotopic composition of lead (Pb) in fugitive dust suspended by a vehicle from 13 unsurfaced roads in Missouri was measured to identify the source of Pb within an established long-term mining area. A three end-member model using 207 Pb/ 206 Pb and concentration as tracers resulted in fugitive dust samples plotting in the mixing field of well characterized heterogeneous end members. End members selected for this investigation include the 207 Pb/ 206 Pb for 1) a Pb-mixture representing mine tailings, 2) aerosol Pb- impacted soils within close proximity to the Buick secondary recycling smelter, and 3) an average of soils, rock cores and drill cuttings representing the background conditions. Aqua regia total concentrations and 207 Pb/ 206 Pb of mining area dust suggest that 35.4e84.3% of the source Pb in dust is associated with the mine tailings mixture, 9.1e52.7% is associated with the smelter mixture, and 0e21.6% is associated with background materials. Isotope ratios varied minimally within the operational phases of sequential extraction suggesting that mixing of all three Pb mixtures occurs throughout. Labile forms of Pb were attributed to all three end members. The extractable carbonate phase had as much as 96.6% of the total concentration associated with mine tailings, 51.8% associated with smelter deposition, and 34.2% with background. The next most labile geochemical phase (Fe þ Mn Oxides) showed similar results with as much as 85.3% associated with mine tailings, 56.8% associated with smelter deposition, and 4.2% asso- ciated with the background soil. Published by Elsevier Ltd. 1. Introduction There are many miles of unsurfaced roads in rural Missouri mining districts that are responsible for generating large quanti- ties of fugitive dust from vehicle traffic. The concentrations of Pb in this dust are substantially higher than those for non-mining areas and have the potential for being a human health concern especially in young children (Witt et al., 2014; Murgueytio et al., 1998). The proximity of these contaminated dusts to mining, ore processing, and smelting operations suggests that the source is the supporting industry of the region. However, Pb in geologic material has shown, through the use of isotopic ratios, to be a combination of several sources to include natural background derived from the parent rock, the historic use of leaded gasoline, ore spillage and wind-blown mine tailings, smelter emissions, and regional aerosols that include a mixture of Pb from many sources (Sakata et al., 2000; Kom arek et al., 2008; Pribil et al., 2014; Rabinowitz and Wetherill, 1972). Isotopic ratios can be a useful tool in supporting mitigation strategies for clean-up of mining area fugitive road dust because they can be used to characterize the anthropogenic sources and support apportionment among established end members. The rationale for using isotope ratios to define the source of Pb in the environment is borne out of the fact that the isotopic composition of Pb reflects both the age of the source and its geological history. Additionally, Pb isotopes do not substantially fractionate during natural or anthropogenic processes, thus their compositions can be used as geological tracers (Faure, 1986; Bollhӧfer and Rosman, 2001). Kom arek et al. (2008) provide an excellent overview of the use of Pb isotopes in environmental * This paper has been recommended for acceptance by B. Nowack. * Corresponding author. U.S. Geological Survey, Center of Excellence for Geo- spatial Information Science, 1400 Independence Road, Rolla, MO 65409, USA. E-mail addresses: ecwitt@usgs.gov, witte@mst.edu (E.C. Witt), mpribil@usgs.gov (M.J. Pribil), jphogan@mst.edu (J.P. Hogan), wronk@mst.edu (D.J. Wronkiewicz). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol http://dx.doi.org/10.1016/j.envpol.2016.05.070 0269-7491/Published by Elsevier Ltd. Environmental Pollution xxx (2016) 1e10 Please cite this article in press as: Witt, III, E.C., et al., Isotopically constrained lead sources in fugitive dust from unsurfaced roads in the southeast Missouri mining district, Environmental Pollution (2016), http://dx.doi.org/10.1016/j.envpol.2016.05.070