Platinum and Lead in South African Road Dust
Automobile traffic is an important source of pollutants, including lead (Pb) and platinum (Pt). The study presented here aims at assessing current levels of these two metals in South African road dust. Pb and Pt concentrations range from 103 to 1,928 μg/g
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Introduction Automobile traffic is an important source of pollutants into the environment. Elevated Pb concentrations have been attributed to the use of tetraethyllead as an anti-knocking additive in gasoline. The recognition of human health effects, especially in children, has resulted in a progressive worldwide phase out of leaded gasoline [1]. Leaded gasoline was banned in South Africa in 2006. Until the ban, Pb was added to gasoline at a concentration of 0.33 g/l. Combined with a gasoline consumption of 7,000 Mt/year, this equates to a Pb consumption of 2,300 t/year, making South Africa the second largest consumer of Pb gasoline additives in Africa [2]. Lead concentrations are now expected to decrease in the South African environment owing to the ban of leaded gasoline. Catalytic converters are placed in the exhaust system of cars to reduce the amount of gaseous pollutants (CO, hydrocarbons and NOx) emitted as by-products of fuel combustion in the engine. Because these catalysts are poisoned by the presence of Pb, the ban of leaded gasoline and the subsequent availability of unleaded gasoline support the introduction of exhaust catalysts in South Africa. Platinum and other Pt group elements are the main active components in catalysts and some Pt is emitted into the environment [3]. As a consequence, Pt concentrations are increasing in the urban and roadside environment [4], and elevated Pt concentrations are now found in airborne particles, road dust, as well as in roadside soil, plants, and biota [5, 6]. Therefore, environmental Pt concentrations are expected to increase in South Africa as a result of automobile emissions. However, South Africa is the
S. Rauch () Department of Civil and Environmental Engineering, Water Environment Technology, Sven Hultins gatan 8, 41296 Göteborg, Sweden e-mail: [email protected] O.S. Fatoki Faculty of Applied Sciences, Cape Peninsula University of Technology, Cape Town, South Africa S. Rauch et al. (eds.), Highway and Urban Environment, Alliance for Global Sustainability Bookseries 17, DOI 10.1007/978-90-481-3043-6_18, © Springer Science+Business Media B.V. 2010
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world’s largest Pt producer [7] and mining activities might be an additional source of Pt. Mining occurs in the Bushveld Igneous Complex, a 65,000 km2 mafic intrusion containing approximately 75% of the world’s Pt resources [8]. Platinum emissions from the mines has until now not been quantified. The study presented here aims at determining current Pb and Pt levels in road dust in South Africa and at assessing the relative importance of automobile and mining emissions. Road dust is an attractive medium for urban pollution studies and it is important to determine current Pb and Pt concentrations in road dust, as Pb concentrations are still high and expected to decrease in the near future, and Pt emissions by automobile traffic are still limited.
Methodology Road dust samples were collected at several locations in Cape Town (2.9 million inhabitants), Pretoria (1.8 millio
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