Solid-Phase Speciation of Pb in Urban Road Dust Sediment: A XANES and EXAFS Study

Abstract

The quality of the urban environment is of growing concern as its human population continues to dramatically increase. X-ray absorption spectroscopy (XAS) and SEM have been used to study the solid-phase speciation of Pb in urban road dust sediments (RDS) in Manchester, UK. XANES analysis and linear combination modeling indicate that PbCrO(4) and Pb-sorbed goethite occur in 1000-500 microm, 250-125 microm, 63-38 microm, and <38 microm size fractions, collectively representing between 51-67% of the contributing Pb-phases. XANES analysis suggests that PbO, PbCl2, and Pb carbonates are also present. EXAFS modeling for all grain size fractions gives best fit models with a first shell of two oxygen atoms at 2.29-2.32 A, which corroborate the possible presence of Pb-sorbed goethite, and also suggest the presence of Pb phosphates and Pb oxides. Second shell Pb-Fe and second and third shell Pb-Pb scattering distances confirm Pb-sorbed to Fe oxide, and PbCl2 and PbCrO4, respectively. Many of the XAS models are corroborated by SEM observations. The Pb-phases may pose a risk to human health if inhaled or ingested, with insoluble phases such as PbCrO4 potentially causing inflammation in the lungs, and soluble phases such as PbO potentially being the most bioaccessible in the digestive tract.

Fractionation and mobility of Cu, Fe, Mn, Pb and Zn in the road dust retained on noise barriers along expressway – A potential tool for determining the effects of driving conditions on speciation of emitted particulate metals

“…Suzuki and Ono (2008) considered PbO 2 as a reducible fraction and PbS as an oxidizable fraction. The F(3)-Pb fraction may also include Pb(II) associated with iron(III) (hydroxide)oxide (Barrett et al, 2010). The results of the chemical resistance test for Pb were consistent with earlier reports.…”

Lead isotope composition and host phases in airborne particulate matter from Budapest, Hungary

“…Sequential chemical extraction of lead from urban dust samples showed that, beside the residual phases, oxidizable, reducible and easily extractable fractions may also contain high amounts of lead (Banerjee 2003). These findings correspond to the observations of Barrett et al (2010) who found that Pb occurs primarily in the form of Pb-sorbed goethite, as well as lead chloride, carbonate, oxide and phosphate in urban dust.…”

“…X-Ray spectroscopy analyses by Barrett et al (2010) showed several lead phases in urban dust, such as surface-sorbed lead, lead chloride, lead carbonate, lead oxide and lead phosphate, which are potentially soluble in weak mineral acids to varying degrees. These are mostly the same phases controlling aqueous-solid partitioning of lead in natural systems.…”

Sources, lability and solubility of Pb in alluvial soils of the River Trent catchment, U.K.

“…Some studies have suggested that roadside soils are still impacted by petrol-derived Pb even after the phasing out of leaded petrol (Bäckström et al, 2004). A number of Pb-bearing species in road dust have low solubility at typical soil pH and E h values, and therefore are likely to persist (Barrett et al, 2010). Along with direct aerosol deposition, other pathways in which road dust could be incorporated into the alluvial soils are either from direct road drainage or drainage derived from sewage works that feed into the Trent and has been dispersed by flooding.…”