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

摘要

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, and Pb-sorbed goethite occur in 1000-500 μm, 250-125 μm, 63-38 μm, and <38 μm size fractions, collectively representing between 51 -67% of the contributing Pb-phases. XANES analysis suggests that PbO, PbCl_2, 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 PbCl_2 and PbCrO_4, 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 PbCrO_4 potentially causing inflammation in the lungs, and soluble phases such as PbO potentially being the most bioaccessible in the digestive tract.