Fate and Transport of Metals and Particulates within the Roadside Environment – A Review

Cory D. Lancaster1, Marc W. Beutel2

1 CDM, 100 Pringle Avenue, Suite 300, Walnut Creek, CA 94596, USA, +1.925.933.2900, This e-mail address is being protected from spambots. You need JavaScript enabled to view it

2 Washington State University, Department of Civil and Environmental Engineering, Pullman, Washington, USA

 

Abstract

This review paper summarizes the research into the fate and transport of the contaminants such as metals and particulates generated by automobiles. Sources of metals and particulates are covered. Macro-, meso-, and micro-scale transport mechanisms within the roadside environment are discussed. Macro-scale mechanisms are a function of regional meteorology and land use. Meso-scale mechanisms include localized traffic conditions and physical roadway geometry. Micro-scale transport mechanisms are highly dynamic and complex functions of physical, chemical and temporal characteristics. The impact of metals on terrestrial organisms is summarized. While lead, the most well known toxic contaminant associated with automobiles, is no longer loaded to roadside environments, it is responsible for much of the interest and research presented in this paper.

Keywords: Automotive contaminants, metals, particulates

 

 

Introduction

Automobiles generate particulate and metal contaminants that exist in clouds around automotive corridors. These contaminants settle on roads, adjacent vegetation and soils. Typically, these contaminants are stripped from the atmosphere and rinsed from the impervious surfaces during precipitation events and depending upon site specific conditions, may ultimately be transported into receiving waters through drainage systems and/or indirect runoff. Where drainage systems do not exist and runoff is insufficient to reach receiving waters, terrestrial environments become the primary sink for the stormwater pollutant loads, adding to the contaminants that have accumulated on nearby vegetation and soils through atmospheric deposition. In this way the terrestrial environments adjacent to highways accumulate and concentrate contaminants. Of high concern are heavy metals due to their relative toxicity and tendency for bioaccumulation. Particulates are also of significant concern as metals tend to partition onto particulate matter. Following is a review of the published literature summarizing the influencing variables, transport mechanisms, and fate of particulates and metals in roadside environments.

Source of metals

Contaminants associated with transportation are generated from a variety of sources. Metal species, including Pb, Zn, Cd, and Cu, are generated from mechanical friction of engine and suspension systems, break pad and tire wear (Hewitt and Rashed, 1990; Muschack, 1990), and undercarriage and auto body rust and corrosion. Also, metal debris and lead tire weights (Root, 2000) fall off of vibrating automobiles. These particles and metal pieces are further ground mechanically between tires and the road surface to fine particulates (Sansalone and Buchberger, 1997b), and are subject to elemental desorption and corrosion (Matthes et al., 2002). Most particulates are generated from tire (20-30% of total) and pavement abrasions (40-50% of total) (Sansalone and Tribouillard, 1999). Zinc plated traffic railings are also susceptible to ion desorption and can contribute to zinc loadings (Legret and Pagotto, 1999).