Road dust is an earthen material or dirt that is transported by air, mainly by the friction of tires moving on unpaved dirt roads and dust-covered paved roads.
Urban areas have high population density and intensive anthropogenic activities, which have a considerable influence on human health. Heavy metals are introduced into the environment through domestic waste, the chemical industry, and transportation.
Roadside soil serves as a stockpile for pollution originating directly from vehicle sources. It could easily come into contact with pedestrians and people residing within the vicinity of the roads.
A variety of pollutants are present in road dust soils, including organic contaminants, various metals such as Pb, As, Zn, Ba, Cu, Sb, Mn, V, Cr, Ni Co, Cd, Pt, Pd, Rh, etc. Cu, Zn, and Cd contaminate the soil samples as they are integral parts of car components. The level of lead level in the environment is continuously increasing because of its use in leaded gasoline, in addition to its applications in lead wheel weights and yellow road paint. A major source of Cu, Cd, Ni, Sb, Cr, and Zn is the abrasion of brake lines. Corrosion of cars and chrome plating of cars are believed to be sources of Ni and Cr in street dust.
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Emissions from fossil fuel combustion, industrial activities, the widespread use of pigments and pesticides, and other human activities reported in recent years are considered sources of arsenic in soil. Gasoline was reported to contain 30–120 ng/g of As. Coal burning, municipal solid waste incineration, the electronic, paper, and pharmaceutical industries were identified as the major sources of anthropogenic emissions of Hg. It has also been reported that several kinds of gasoline contain 0.2–3.3 ng/g of Hg.
Heavy metals are non-biodegradable, and they cause hazardous effects on biological systems, humans, soil biota, animals, and plants. As they are non-biodegradable, they can persist in soil for decades or even centuries.
The investigation of road dust for heavy metals is important for the following two main reasons.
- Firstly, street dust is freely inhaled by those traversing the streets and those residing within the vicinity of the streets. The more the dust on such streets becomes contaminated with heavy metals, the more people are exposed to the health hazards associated with such metals.
- Secondly, when it rains, the dust usually gets discharged into the adjoining aquatic and marine environments, and thus it may seriously pollute the water and concentrate in the surface sediments of the coastal area. This might prove toxic to marine life, and at worst it may contaminate fish or shellfish, which could have adverse direct impacts on the health of individuals that consume seafood.
Thus, there is a need to regulate heavy metals and institute countermeasures against heavy metal pollution.
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