『Abstract
　A blackish, sandy material (‘blackish deposit’, BD) accumulates on highway roadsides. Few years after road opening it may reach several centimeters of depth. Comparison of BD rates of accumulation with reported loads of suspended solids in highway runoff suggests blackish deposits to originate both from suspended solids in road runoff and from aerial depositions. This study of four Danish highways shows that BD is considerably different from the original surface (OS) materials. Compared to OS-materials, BD-materials are clearly darker, contain more organic matter (4-8％ versus around 1％ in OS), have a high and less-variable content of clay and metal oxides, and a slightly lower bulk weight and pH. Similar clay mineralogy points to both BD and OS to be of local origin. Both materials contain lime (calcite). The textural border between BD and OS is also a sharp border between different levels of soil contamination: Zn up to 330 mg/kg in BD versus 19-63 mg/kg in OS, Pb up to 210 mg/kg versus 5-33 mg/kg, Cr up to 250 mg/kg versus 3-10 mg/kg, Cd up to twice as high in BD as in OS, Br and As markedly higher in BD than OS, heavy mineral oils (nC25-nC35) up to 680 mg/kg versus 16-24 mg/kg, and sum of PAH up to 1.4 mg/kg versus ＜0.05-0.72 mg/kg. The continuous deposition of organic matter, calcite, metal oxides and clay suggest that BD, in addition to particles, is able to accumulate dissolved contaminants from infiltrating road runoff.

Keywords: soil pollution; blackish deposits; highways; heavy metals; PAH; THC』

1. Introduction
2. Materials and methods
　2.1. Sample material
　2.2. Sample preparation and analysis
3. Results
　3.1. Colour, bulk weight, pH, and texture
　3.2. Clay mineralogy and CBD-extractable Al and Fe in clay fraction
　3.3. Element distribution according to EDXRF
　3.4. Heavy metals
　3.5. THC and PAH
4. Discussion
　4.1. Overall characteristics and composition
　4.2. Wet or dry weather deposition
　4.3. Mitigation potential of blackish deposits
5. Conclusions
Acknowledgement
References

• Dierkes,C. and Geiger,W.F.(1999): Pollution retention capabilities of roadside soils. Water Science and Technology, 39, 201-208.
• Jensen,M.B.(2004): Hydrological conditions for contaminant leaching through highway swales. Water, Air, and Soil Pollution, 158, 169-180.
• Lee,P.K. and Touray,J.C.(1998): Characteristics of a polluted artificial soil located along a motorway and effects of acidification on the leaching behavior of heavy metals (Pb, Zn, Cd). Water Research, 32, 3425-3435.
• Mikkelsen,P.S., Haflinger（aの頭に¨）,M., Ochs,M., Jacobsen,P., Tjell,J.C. and Boller,M.(1997): Pollution of soil and groundwater from infiltration of highly contaminated stormwater - a case study. Water Science and Technology, 36, 325-330.
• Pagotto,C., Remy（eの頭に´）,N., Legret,M. and Cloirec,P.Le.(2001): Heavy metal pollution of road dust and roadside soil near a major rural highway. Environmental Technical, 22, 307-319.
• Turer,D.G. and Maynard,J.(2003): Heavy metal contamination in highway soils. Comparison of Corpus Christi, Texas and Cincinnati, Ohio shows organic matter is key to mobility. Clean Technology and environmental Pollution, 4, 235-245.