THE METROPOLITAN SCENARIO
A procedure was used to study the major toxic metals and its patterns in Karachi metropolis with the help of cartographic techniques that furnished Figures 1, 2, 3, 4, 5 and 6 for iron, lead, Cadmium, Manganese, Copper and Zinc respectively.
Fig 1 Spatial Patterns of Iron (Fe)
Fig 2 Spatial Patterns of Lead (Pb)
Fig 3 Spatial Patterns of Cadmium (Cd)
Fig 4 Spatial Patterns of Manganese (Mn)
Fig 5 Spatial Patterns of Copper (Cu)
Fig 6 Spatial Patterns of Zinc (Zn)
The natural sources of particulate matter in Karachi metropolis could be sea salt, dust storms and soil entrainment. Human-induced particle emissions result from sources such as cars, trucks, steel mills, cement factories, ceramic industries and solid waste open burning. In which, a major contributing factor to urban soil deposits is the extensive use of road transport in urban areas. Road transport has already become the major mode of transportation both for passengers and goods. The total number of all types of motor vehicles on road in Karachi is estimated to be 1 million in December 2001 and it is expanding with an explosive growth rate.
Among all analysed heavy elements found in urban region as a pollutant, lead is a non-degradable and toxic element. It leads to harmful effects on human beings. It creates number of abnormalities in human body, such as Anaemia, Diarrhoea, Jaundice, Headaches (WHO, 1987; Wellburn, 1994; Olivi et al., 2002) and Excessive lead in urine are the signs and symptoms of the abundance of lead in blood (Yousufzai et al, 1994). Lead influences the nervous system, slowing down nerval response. This influences learning abilities and behaviour (NAS, 1972, Grant and Davis, 1990). Children are exposed to lead right from their birth, as children in the embryonic stage receive lead from their mothers through the blood (McMichael et al., 1986). Children are furthermore exposed to lead through dust and soil contaminated by deposition from air and other sources (Barltrop, 1972). The principal source of lead is the combustion of leaded gasoline used in automobiles. Table 1 shows the relationship between lead concentration and road proximity by comparing the distances. Besides this, lead is also being used in number of industries as an essential manufacturing element. Paint, pipe making, dye-making and batteries manufacturing industries are the appropriate examples of generating lead. Lead is very harmful toxic element. Manganese, cadmium, iron, copper and zinc are also very harmful and poisonous metals. Cadmium for instance, accumulates in the kidneys leading to dysfunction of the kidney with increased secretion of proteins in urine and other effects (ECDGENV.E3, 2002). Their major emission sources are industrial wastes and vehicle emission (Prokop et al., 2003). In Karachi metropolis Sindh Industrial Trade Estate (SITE) and Korangi Industrial Trade Estate (KITE) are the major industrial zones. These areas are enriched in toxic metals as indicated by samples number 1, 3, 4 and 11 in Table 1.
GIS enables us to look into the cause and effect relationship with visual presentation. Developed figures clearly show the major emission sources. The main concentration of lead, manganese, copper, zinc and iron are along dense traffic locations, choking nodes and major industrial zones. Nevertheless, wind direction, wind speed and elevation also play vital role to better understand the spatial distribution within a particular region (Jian and Rocke, 1997; Navas and Lindhorfer, 2003). Contamination of these pollutants in water and soil are also caused by the same factors (Board, 1969; Parekh et al., 1987 and 1989). The difference between abundances of trace elements in the Mason Earth Crust (viz Mn - 950 ppm, Fe - 50 ppm, Cu - 55 ppm, Zn - 70 ppm, Cd - 0.2 ppm and Pb - 13 ppm) and monitored concentration levels conclude that Karachi urban soil is heavily being enriched in toxic metals by industrial process and day-to-day activities of its citizens.
Using the rank summation method, risk evaluation has been performed (as used by Kazmi, 1996). Table 2 shows Tibet Centre, Siemen's Chawrangi, HBL Nazimabad, SITE Police Station, water pump and Jail Chawrangi, which are the major high-risk Locations. Nursery, Hasan Square, Nazimabad, Garden, Nagan Chawrangi and Gurumandar are recognized as moderate risk areas of Karachi. While Mangho Pir, Defence, Malir City, Quaidabad, Korangi and Landhi are found as low risk area. These results are confirmed to the distribution of traffic routes and industries within Karachi metropolis (refer to Table 1).
Table 1 Accumulation of heavy metals in urban soil
Table 2 Major Risk Locations in Karachi Metropolis
