Heavy metals are natural components of the earth’s crust that are non-degradable and
wastewater discharges, and manufacturing facilities are the common pathways to the environment (Kampa & Castanas, 2008). Road traffic represents one of the main sources of dispersion of heavy metal pollution (Hjortenkrans et al., 2006). This implies that the presence of heavy metals near roads may signify emissions of exhaust gasses, brake wear, tyre wear and wear of mechanical parts due to friction. Metals such as zinc, copper, barium, and lead originate from brake lining wear (Laschober et al., 2004) but heavy metals of concern associated with brake wear emissions include
Lead, Zinc, Cadmium, Copper, Nickel, Antimony (Sb), and Chromium (Li et al., 2001 & Sörme et al., 2001). Resuspension of soil and road dust also represent a major potential source for metal emissions (Thorpe and Harrison, 2008; Laschober et al., 2004). The presence of Zn, in addition to traces of Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni and Pb represent tyre or mechanical abrasion of body car part emissions, while Cd, Cr, Cu, Ni, Pb and V are exhaust fume emissions originating from fossil fuel combustion (Hjortenkrans et al., 2006). Other metals of concern related to vehicle tyres, especially because tyres have been linked to traceable levels of several metals, include Cadmium, Cobalt, Chromium, Copper, Mercury, Manganese, Molybdenum (Mo), Ni and Pb (Davis et al., 2001; San Miguel et al., 2002). Combustion of leaded petrol and motor oils commonly represent important sources of some heavy metals (Laschober et al., 2004). However, with the ban of leaded petrol in Europe, lead emissions from traffic has been considerably reduced, yet fossil fuel combustion remains the source of some emissions of Cd, Cr, Cu, Ni, Pb and V (Ozaki et al., 2004 & Cadle et al., 1999). Prior to the phase-out of leaded petrol, it has remained the major source of heavy metals with lead as the heavy metal mostly associated to traffic emissions (Rode et al., 2010) but currently, Cu, Zn, and Pb represent the most
important traffic-related heavy metals while the source of other heavy metals may vary (Van Bohem and Van de Laak, 2003).
Lead (Pb) is a heavy metal whose emission source is fuel combustion in road transport in Europe (Pacyna et al., 2007). Naveed et al. (2010) studied lead pollution of roadside using plant leaves as bioindicator, found higher deposition of heavy metals, e.g. lead, in plants near roadways, and therefore concluded that higher vehicular densities and the distance from roadways influenced this. Although there are other sources of Pb including smelting, fabrication processes or paint manufacture, disposal of unwanted lead-containing materials, and combustion of coal, Lam et al. (1999) revealed that lead discharged from automobile exhaust constitutes the major source of atmospheric lead.
Copper is another metal produced by transport and enters the air, mainly through release during the combustion of fossil fuels, and finally deposited on different surfaces including leaf, grass, and soil. The main sources are coal combustion, public power generation and road transport. Interestingly, the decline in oil and heavy fuel oil combustion has contributed to corresponding decline in Cu emissions (Dore et al., 2007).
2.8.5.2 Health concerns of Heavy Metals
Among the heavy metals, lead has become so important due to their toxicity and constant increase in the environment (Naveed et al., 2010). The common pathway of lead into human bodies include consumption of unwashed food supplies, especially those within the roadways, and inhaling contaminated air, especially pedestrians walking along heavily trafficked roadways. Lead can bio-accumulate in human body
and can become toxic at low dose concentrations (Järup, 2003). Lead has been associated to certain diseases that have lethal effects on man and animals (Silva et al., 2005; Michalke, 2003). On contact with the eyes and nose, Pb dust or fumes can cause irritation, and on inhalation, can cause irritation to throat. While the consequences of acute exposure to Pb include loss of appetite, weight loss, stomach upsets, nausea and muscle cramps, high levels of acute exposure may lead to brain and kidney damage and the resultant effect of chronic exposure can lead to effects on the blood, kidneys, central nervous system and vitamin D metabolism (Dore et al., 2007).
Exposure to Cu fumes can result in acute effects such as irritation of the eyes, nose and throat, coughing, wheezing and nosebleeds. Such exposure can also result in a flu-like illness with symptoms of a metallic taste, fever, chill, aches and chest tightness. Effect of chronic exposure to Cu may include decreased fertility in men and women as well as severe irritation and ulcers in the nose (Dore et al., 2007).
2.9 Conclusion
This chapter looked at air pollutants, their sources and contributions to air quality. Vehicular traffic remains the major source of air pollutants and both distance and height had significant influence on the concentration levels of pollutants. Different factors contributed to the temporal and spatial distribution of air pollutants including high traffic volume, meteorological parameters, landscape, and car and driving conditions. The epidemiological and ecological impacts of air pollutants elicit several adverse effects on human health, plant growth, infrastructural damages, acid rain, and global warming. These concerns necessitated the provision of set limits for the pollutants.
Chapter Three
3.0 Introduction
The previous chapter reviewed different approaches for measuring different air pollutants. It is a common practice in air monitoring studies to carry out field sampling and subsequently prepare them for laboratory analysis. While some devices generate on-the-field data, others may need further laboratory preparations. This chapter will consider, in details, the different sampling techniques and their applications in generating useful data for the study analysis.