Solid-phase speciation of Zn in road dust sediment

Abstract

ABSTR ACT X-ray absorption spectroscopy, scanning electron microscopy (SEM) and X-ray diffractometry (XRD) have been used to study the solid-phase speciation of Zn in urban road dust sediments (RDS) in Manchester, UK. X-ray absorption near-edge structure (XANES) analysis using linear combination modelling suggest that the soluble species Zn(NO 3 ) 2 ·6H 2 O and ZnCl 2 represent 70À83%, and Zn-sorbed goethite 17À30%, of the Zn species present. The presence of goethite is not corroborated by extended X-ray absorption fine structure (EXAFS) modelled first shell scattering ZnÀO distances of 2.01À2.03 Å , but this may be due to distortion of the Zn octahedra on the goethite surface, or the existence of Zn-sorbed species with other metal hydrous oxides, as inferred by the EXAFS-modelled second shell Fe and Al scatterers. Analysis by EXAFS also suggests that metallic Zn-Cu-Sn-Pb and Zn-silicate phases are present in the RDS, and this is corroborated by SEM and XRD. Other phases suggested by EXAFS include ZnO, franklinite, Zn-sorbed birnessite and zinc formate. Differences between the XANES and other results suggest that model compounds such as Zn-bearing phyllosilicates and metallic Zn phases may have been missing from the XANES fitting. Long-term low-level exposure to the RDS Zn phases identified may lead to an increased risk of cardiovascular or pulmonary diseases.

Characterisation of road-dust sediment in urban systems: a review of a global challenge

“…Only small amounts of carcinogenic Cr(VI) were detected. In similar studies, Barrett et al (2010Barrett et al ( , 2011 used XAS techniques to establish the speciation and potential toxicity of Pb and Zn in RDS, respectively. These studies established the main metal-bearing phases for these metals in the RDS and hence the pathways by which they could pose a threat to human health.…”

Zinc Speciation in the Suspended Particulate Matter of an Urban River (Orge, France): Influence of Seasonality and Urbanization Gradient

“…Accordingly, the presence of such alloys was recently observed in the road dust of Manchester City, UK. 42 During rain events, microfragments of such material can be transported by runoff to the river and/or eventually be resuspended from bottom sediments. ZnS nanoparticles were observed by TEM in SPM (SI Figure S3c), which is consistent with the previous observation of ZnS in the SPM of the Seine River downstream of the Paris conurbation.…”

“…Such Zn-containing alloys were formerly used to manufacture screws, bolts and other machined pieces. Accordingly, the presence of such alloys was recently observed in the road dust of Manchester City, UK . During rain events, microfragments of such material can be transported by runoff to the river and/or eventually be resuspended from bottom sediments.…”

“…In the Paris region (France), runoff on roads and on urban galvanized structures such as roofs , are known as important sources of Zn input to the Seine River basin . Zn speciation determined in previous studies indicated dramatic differences between road dust deposits, riverbed or SPM samples . In the SPM of the Seine River, Zn was mainly found to be associated with Fe-oxyhydroxides, calcite and clay minerals upstream from Paris, and significant contributions from Zn sulfide were evidenced downstream of Paris .…”

“…In riverbed sediments, under anoxic conditions, species such as Zn-sulfide or Zn incorporated into vivianite (Fe 3 (PO 4 ) 2 ) have also been recognized as possible Zn-bearing phases . In SPM, solid-state speciation of Zn may exhibit spatial and temporal variations due to fluctuations in geogenic and industrial inputs, to urban runoff from road and galvanized surfaces, to sewage discharges and to seasonal changes in water flow conditions. , Further studies are thus needed to better understand the complex interplay between these environmental factors and to evaluate the role of SPM as a reactive vector in the biogeochemical cycles of trace elements, such as Zn erosion or pollution processes.…”