Determination of lead and other metals in a residential area of greater Calcutta.

The aim of the study was to determine the major source and extent of metal pollution in a residential area of Greater Calcutta. In this area approximately 50,000 people reside in the vicinity of a lead factory that produces lead ingots and lead alloys. Many people, especially children, are affected by lead toxicity. Soils, waters, road dust, leaf dust, leaves and pond sediments were sampled in and around the factory area. Aliquots of the samples were mineralized with nitric acid and hydrogen peroxide in a microwave system. Lead and 19 other elements were quantified in the digests by inductively coupled plasma mass spectrometry. The performance of the procedure was confirmed by analyzing NBS-BCR standard reference soil, leaves, sediment samples. The soils are highly contaminated not only with lead (4.7%), but also with Cd (0.08%), Ag (0.001%), Cu (0.02%), Zn (1.0%), As (1.0%), Mo (0.003%), Sn (0.003%) and Hg (0.03%) (metal concentrations given in parentheses are maximum). Moving away from the smelter, most of metal concentrations, especially Pb, As, Mo, Cu, Hg, Zn, Cd, Sn and Ag, decreased exponentially over increasing distance. In the residential areas near the smelter, notably to the west side of the factory, metal concentrations significantly breached the threshold trigger values set in India by the Central Pollution Control Board (CPCB). Particulate materials from the smelter stack appear to contaminate soils up to at least 0.5 km. However, abnormally high metal levels in the immediate smelter area may be due to primarily fugitive emissions. The surface waters are only contaminated by arsenic ranges from 0.05 to 13.5 mg/l, but the ground water is currently not polluted by lead and arsenic. An appropriate treatment plant with some intervention measures should be taken to save the locality.