The soil distributed at the boundary between roadway and pavement in urban areas, hereafter designated road sediments, usually contain various kinds of microscopic artificial materials. Road sediment samples were collected from three cities in Kyoto Prefecture. Microscopic observations and chemical analyses were carried out for these samples in order to assess its applicability to forensic science.
In addition to glass beads, traffic paint segments, rubber fragments and asphalt grains, various kinds of metal fragments such as iron, copper, aluminum and brass are found in the road sediments collected from the urban center of Kyoto City.
Major and trace element concentrations were determined for the <74μm fraction in the road sediments by X-ray fluorescence spectrometer. The present measurements indicate that heavy metals are mostly enriched in the road sediment samples relative to background samples (surface weathered sediments) distributed around Kyoto City.
The enrichment factors (EF) of copper and zinc decrease with the increase of grain sizes, whereas the EF values of alkaline elements and silicon increase with the increasing grain size. It is likely that the copper concentrations in the road sediments are proportional to the traffic volume. The source of copper contained in the road sediments may be the breaking pads of vehicles.
There is no significant annual variation of chemical compositions in the road sediments. Abundance of chromium, nickel and lead in the Maidzuru samples are greater than the Kyoto samples, suggesting that chromium in the Maidzuru samples is derived from chromian spinels contained in ultra-basic rocks.
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