Legacy Lead from Past Mining Activity and Gasoline Additives: Evidence from Lead Isotopes and Trace Element Geochemical Studies in the White River Basin, Southern Ozark Region, USA

Lead isotope compositions and Pb, Cu, Zn, and As concentrations in stream sediment leachates in the White River Basin, southern Ozark Region, have been determined to discriminate between natural and anthropogenic sources of Pb and to assess the metal loads that are transported by streams draining the Mississippi Valley-type (MVT) Zn-Pb mines in the Northern Arkansas district. The samples that were collected downstream of and closest to the mines have trace element concentrations well above those in soils from Arkansas. The trace element concentrations are lower in samples that were collected upstream of the mines. Most of the analyzed samples have trace metal concentrations above the United States Environmental Protection Agency (USEPA) Sediment Quality Guidelines Threshold Effects Level. The Pb isotope values of the downstream samples and the MVT ores are similar, suggesting a similar Pb source. The Pb isotope values of the upstream samples are similar to those that were defined by soils from the Ozark Plateau, suggesting that Pb from historic mining does not dominate upstream sediments. However, a linear regression line through the leachate data indicates that mixing between two end-members represented by leaded gasoline and ores could generate the Pb isotope ratios that were noticed in the upstream leachates