Metal accumulation in roadside soil in Melbourne, Australia: Effect of road age, traffic density and vehicular speed Shamali De Silva a, d, * , Andrew S. Ball b, d , Trang Huynh c , Suzie M. Reichman a, d a School of Civil, Environmental and Chemical Engineering, RMIT University, Melbourne 3001, Australia b School of Applied Sciences, RMIT University, Melbourne 3001, Australia c Centre for Mined Land Rehabilitation, Sustainable Mineral Institute, The University of Queensland, Brisbane, QLD 4072, Australia d Centre for Environmental Sustainability and Remediation, RMIT University, Melbourne 3001, Australia article info Article history: Received 15 April 2015 Received in revised form 9 September 2015 Accepted 10 September 2015 Available online xxx Keywords: Roadside soil Vehicular emissions Road age Vehicular speed Traffic abstract Concentrations of vehicular emitted heavy metals in roadside soils result in long term environmental damage. This study assessed the relationships between traffic characteristics (traffic density, road age and vehicular speed) and roadside soil heavy metals. Significant levels were recorded for Cd (0.06 e0.59 mg/kg), Cr (18e29 mg/kg), Cu (4e12 mg/kg), Ni (7e20 mg/kg), Mn (92e599 mg/kg), Pb (16 ndash;144 mg/kg) and Zn (10.36e88.75 mg/kg), with Mn concentrations exceeding the Ecological Investigation Level. Significant correlations were found between roadside soil metal concentration and vehicular speed (R ¼ 0.90), road age (R ¼ 0.82) and traffic density (R ¼ 0.68). Recently introduced metals in automotive technology (e.g. Mn and Sb) were higher in younger roads, while the metals present for many years (e.g. Cd, Cu, Pb, Zn) were higher in medium and old age roads confirming the risk of significant metal deposition and soil metal retention in roadside soils. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Australia has a total of 800,000 km of road network system, with about 0.06 km per capita of road network system. Melbourne is an urban metropolitan area of 9900 km 2 and population of 4.4 million people, one of the most densely populated areas in Australia (ABS, 2012). Many residential estates are erected beside roads and as a result highly prone to pollution such as vehicular emissions. Vehicular emissions include metals 1 which end up in roadside soil (Li et al., 2003). These metals come from fuel (As, Cd, Cr, Hg, Mn, Ni, Pb, Se and Zn), engine oil (Cd, Cr, Ni, Zn and W), tyre wear (Cd, Co, Cu, Cr, Pb, Ni, Se and Zn), brake wear (Ag, As, Cd, Cu, Cr, Ni, Pb, Sb and Zn) and vehicular exhaust catalysts (VEC) (Pt, Pd and Rh) (Hjortenkrans et al., 2006, 2007; Li et al., 2001; Ravindra et al., 2004; Whiteley and Murray, 2003; Wichmann et al., 2007; Winther and Slento, 2010; Zereini and Alt, 2006). In the last 25 years, a number of new metals have been incorporated into auto- motive technologies which are now being introduced into the environment as a result of vehicular movement. These include Sb in brake pads as a replacement for asbestos (Hjortenkrans et al., 2007), Mn in fuel as a replacement for Pb, and Pt group metals in VEC's to reduce air pollution (Morcelli et al., 2005; Rauch et al., 2005; Wichmann et al., 2007). These metal emissions accumulate in the urban environment over time (Sternbeck et al., 2002; Wong et al., 2006; Yassoglou et al., 1987) and show low levels of leaching (Radha et al., 1997). Thus, even once vehicle emissions stop (e.g. Pb in petrol), roadside soil concentrations and potential effects are likely to persist for a long period of time. Urban areas are highly populated and as a result contaminated urban soil will have po- tential effects on human health and ecological systems (Li et al., 2004). Vehicular-emitted metals can be dispersed up to 100e200 m from roadsides, although the majority are deposited within 20 m of the road edge (Dan-Badjo et al., 2008; Trombulak and Frissell, 2000). Factors which tend to result in further metal dispersion include rain, wind and gravity (Trombulak and Frissell, 2000; Wong * Corresponding author. School of Civil, Environmental and Chemical Engineer- ing, RMIT University, Melbourne 3001, Australia. E-mail address: shamali.desilva@rmit.edu.au (S. De Silva). 1 Throughout this study use of the term ‘metal’ includes metals [such as Ag (silver), Cd (cadmium), Cu (copper), Cr (chromium), Mn (manganese), Mo (mo- lybdenum), Ni (nickel), Pb (lead), Zn (zinc) and W (tungsten)], platinum group el- ements (PGE) [such as Pt (platinum), Rh (rhodium) and Pd (palladium)]as well as metalloids [such as As (arsenic) Sb (antimony) and Se (selenium)]. Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol http://dx.doi.org/10.1016/j.envpol.2015.09.032 0269-7491/© 2015 Elsevier Ltd. All rights reserved. Environmental Pollution xxx (2015) 1e8 Please cite this article in press as: De Silva, S., et al., Metal accumulation in roadside soil in Melbourne, Australia: Effect of road age, traffic density and vehicular speed, Environmental Pollution (2015), http://dx.doi.org/10.1016/j.envpol.2015.09.032