wAbstract
@Road-deposited sediment (RDS) is an accumulation of particulates
upon street surfaces in urban centres. It is commonly highly contaminated
and has major potential impacts upon surface water quality and
human health, as well as becoming a waste material upon street
sweeping. Although significant research has been undertaken upon
the fine fraction within these systems, there is a lack of detailed,
high-resolution grain-specific mineralogical and chemical data
for the coarser fractions, which contain the bulk of the contamination
by mass. The study reported here utilizes backscatter electron
microscopic, electron microprobe and Raman spectroscopic analysis
to provide novel data on RDS material from Manchester, UK, with
significant implications for the improved understanding of source
discrimination and contaminant metal speciation. The RDS samples
studied are highly heterogeneous and the abundant nature of anthropogenic
grains is particularly apparent. The RDS material has been found
to be composed of a number of grain types: (i) silicate and alumino-silicate
grains derived from a wide range of sources; (ii) iron oxide grains
derived from the corrosion of galvanized steel; (iii) iron-rich
glass grains derived as slag material from metal and waste processing
activities and 'iv) spherical Fe oxide and Fe-rich glass grains
derived from high temperature combustion processes. Elemental
metallic grains (Fe, Cu, Pb) are also present in minor amounts.
@Electron microprobe analysis shows that the Fe oxide and Fe-rich
glass grains act as the major hosts for contaminant metal elements
within these sediments. The recognition of Fe oxides being an
important host for metals is consistent with previous inferences
made from bulk chemical sequential analysis. However, the presence
of glass slag phases as major hosts of metals is not recognised
in these sequential extraction schemes, leading to erroneous inferences
and inputs into risk assessments.It is clear that high resolution
grain-specific chemical analysis, as reported here, is the key
to fully understanding these urban contaminated sediment systems.x
1. Introduction
2. Study area, materials and methods
@2.1. Study area and sediment sampling
@2.2. Sample analysis
3. Results
@3.1. Silicate and alumino-silicate grains
@3.2. Iron oxide grains
@3.3. Iron-rich glass grains
@3.4. Accessory grain types
4. Discussion
@4.1. Nature and sources of grains
@4.2. Implications for contaminant speciation assessment
5. Conclusions
Acknowledgements
References