Sources of atmospheric lead (Pb) in and around an Indian megacity

Abstract

Lead (Pb) is a toxic metal whose global anthropogenic fluxes are an order of magnitude higher than natural fluxes. Among all the environmental compartments, the atmosphere is the major initial recipient of Pb. To minimize the exposure to this toxic metal, it is important to determine the potential sources of atmospheric Pb. This study uses a multiproxy approach, Pb isotopes in conjunction with metal composition of aerosols to determine the possible sources of anthropogenic Pb in the atmosphere, in and around an Indian megacity, Kolkata. In Asia, India is the second largest atmospheric Pb emitter after China through coal combustion. Indian automobile and high temperature metallurgy industries are growing rapidly and Pb emissions from India can be traced as far south as in Chagos Island in the Indian Ocean. This study investigates the anthropogenic sources of atmospheric Pb in eastern India at three locations along a 150 Km N-S stretch. The locations have very different environmental settings; a pristine river island, a megacity, and an industrial town. Pb isotope and metal compositions indicate different sources of atmospheric Pb for the three locations: gasoline exhaust from road and riverine traffic in the island, emissions from the high temperature metallurgy industry in the industrial town and long-range transport of coal combustion and industrial emissions for the megacity. The Pb isotope ratios (206Pb/207Pb = 1.1155–1.1681 and 208Pb/207Pb = 2.3905–2.4494) measured in this study have a wider range and are mostly higher than previously measured in Indian aerosols. Pb isotope compositions of two end members, Indian coal and road dust are also measured. This study shows that post leaded gasoline phase-out, the atmospheric Pb emissions in India are dominated by Indian coal combustion and ore processing.