Road deposited sediments (RDS) are a unique aspect of the urban environment, a complex dynamic and mobile system that acts as both sink and source for a variety of potentially toxic inorganic metals, organics and nutrients. Instrumental to the understanding of the nature of RDS and how they cycle in and interact with the urban environments, is the oxidation state, binding form and binding partners of the associated metal contaminants. The aims of the research programme are (i) to provide a comprehensive geochemical and mineralogical analysis of RDS in the urban environment of Oxford Road. Manchester, UK; (ii) to define the physicochemical form and determine, for the metal contaminants Cu, Pb and Zn within the RDS matrix, their true chemical speciation in the solid state, and in so doing improve the understanding of how these contaminant metals cycle within the urban environment thus providing baseline information for determining their effects on human health. Physical and geochemical characterization using grain-fractionation techniques and conventional chemical methodologies show that the grain-size fractions of less than 63 11m account for the smallest percentage mass of the sediment but have the highest concentration of metal contaminants. In contrast, consideration of grain-size mass loading showed that the majority of the contaminant load was carried by grain-size fractions greater than 63 11m. Hazard assessment of the total metal concentrations using (i) adjusted Dutch Intervention and Target Values for RDS. reveal Cu, Pb and Zn to be above their target concentrations. Copper is of particular concern. with concentrations consistently above intervention values and in need of remediation; and (ii) enrichment factors, show that Pb is the most enriched in the Manchester RDS, suggesting that sources of Pb include historic deposits and achieving sustained remediation will require a long time. Scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS), show that quartz grains are the most numerous in the Oxford Road sediments. Iron oxide grains are observed in all grain fractions. The presence of Cu-, Pb- and Zn-bearing grains is also noted in a number of grain-size fractions. Grains of Cu and Pb in association with Cl were detected in the 250-125 11m and 1000-500 11m, respectively. whilst Pb- and Cr-bearing grains were noted in the <38 11m fraction. In addition, intermetallic compounds (e.g. Cu-Sn; Cu- Zn; Pb-Cu and Zn-Sn) were discerned in a number of grain-size samples. X-ray powder diffraction (XRD) traces show that quartz is the dominant crystalline phase all in grain-size fractions. Iron oxide (hematite or magnetite), calcite and felspathic minerals (albite and microcline) are a minor component in all size fractions, and the phyllosilicates kaolinite and chlorite are also minor phases in the 63-38 11m and <38 11m fractions. Trace amounts of Cu metal and Cu chromite are suggested by the XRD data for the heavy mineral separate for the coarsest fraction, whilst the presence of cometite (CuP04) is intimated in the analysis of the 125-63 11m sample. The occurrence of trace quantities of anglesite (PbS04), Pb-apatite, Pb basic carbonate and Pb oxide chloride are indicated also by the XRD data for the heavy mineral separate fractions from all grain fractions (with the exception of the <38 11m fraction). Analysis of XRD diffractograms for the 2000-1000 11m and 125- 63 11mfractions (heavy mineral separate) also suggest that low levels Zn metal and the silicate phase hodgkinsonite (Zn2Mn[Si04](OH)2), respectively. may be also present. XANES analysis and linear combination modelling indicate that 2CUO.Cr203 and Cu-sorbed goethite occur in 1000-500 11m, 250-125 11m, 63-38 11m, and <38 11m size fractions, collectively representing between 34-70% of the contributing Cu-phases, XANES analysis suggests that CuO, CU20, and Cu phosphates are also present. EXAFS modeling for the four grain-size fractions gives best fit models with a first shell of three oxygen atoms at 1.93-1.95 A, which substantiate the possible presence of Cu-sorbed goethite, and also suggest the presence of CuO, CU2(P04)(OH), Cu(C2H302)2.H20 and CuS04·5H20. Second shell Cu-Sn and second and third shell Cu-Cu and Cu- Pb suggests a clear association between and metalliferous phases in the Manchester RDS. Linear combination modelling of the XANES data for Pb phases suggest that PbCr04 and Pbsorbed goethite occur in 1000-500 urn, 250-125 11m, 63-38 11m, and <38 11m 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 occurrence 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 PbCr04, respectively. XANES analysis and linear combination modeling of Zn phases indicate that Zn(N03)2·6H20 is the dominant species all four grain-size fractions, representing between 42-48% of the contributing Zn-phases, XANES analysis suggests that ZnCl2 and Zn-sorbed goethite are also present. EXAFS modeling for all grain size fractions gives best fit models with a first shell of five to six oxygen atoms at 2.0 I-2.03 A. the possible presence of Zn(N03)2·6H20 and Zn-sorbed goethite is not corroborated. Second shell Zn-Fe and Zn-Al scattering distances suggest the presence of Zn-sorbed species on metal hydrous oxides and phyllosilicates, whilst second and third shell Zn-Si suggest that Zn-bearing silicates may contribute to the Zn speciation of the Oxford Road sediments. The identification of individual elemental species allows for the important discrimination of Cu, Pb and Zn phases. Epidemiological studies have shown that species such as CuO. PbCr04 and ZnCI2, identified by XAS analysis to be present in the Oxford Road sediments are of concern to human health.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:532184 |
| Date | January 2010 |
| Creators | Seddon Barrett, Judith Elizabeth |
| Publisher | Manchester Metropolitan University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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