Onset of Industrial Pollution Recorded in Mumbai Mudflat Sediments, Using Integrated Magnetic, Chemical, 210Pb Dating, and Microscopic Methods

The onset and rise of urban and industrial pollution in the Mumbai region was reconstructed from an anthropogenically contaminated mudflat sediment profile from the adjacent Thane creek using magnetic parameters, polycyclic aromatic hydrocarbon (PAH) data, metal contents, and the Pb-210 dating technique. The 1.8 m vertical section at Airoli (Navi Mumbai) reveals an increase of magnetic susceptibility (chi) from background values of (20-50) to (75-100) x 10(-8) [m(3) kg(-1)] in the anthropogenically affected zone above similar to 93 cm. A sharp rise of chi from (75-100) to (130-215) x 10(-8) [m(3) kg(-1)] subdivides the anthropogenically affected zone at a depth of similar to 63 cm. Characterization with rock magnetic parameters (SIRM, Soft IRM, and S-ratio) reveals a significant contribution of ferri(o)magnetic phases in the upper zone. Based on the magnetic classification sampling intervals for cost-intensive PAH and metal analyses were determined. Steadily increasing contents of PAH and metals of anthropogenic origin are observed above the boundary depth at similar to 93 cm. A sediment accumulation rate of 1.2 +/- 0.3 cm/yr provided by Pb-210 dating dates the similar to 63 cm boundary to 1951. Increasing industrial activity, including the establishment of a coal-fired power plant in 1956, and refineries between 1955 and 1960, correlates well with the substantial increase of chi, PAH, and metal contents. Scanning electron microscopy (SEM) investigation on magnetic extracts from the contaminated zone reveals the presence of magnetic spherules derived from industrial high-temperature processes.