Alstonia scholaris R. Br. and Cassia siamea Lamk as possible biomonitors of lead and cadmium in the polluted environment of Karachi city, Pakistan

The leaves of Alstonia scholaris and Cassia siamea were investigated as possible biomonitors of heavy metal pollution in polluted environment of Karachi city. Concentration of heavy metals (lead and cadmium) was determined in unwashed leaves of A. scholaris and C. siamea collected from a wide range of different sites of the city. Difference between lead and cadmium content varied according to the metal pollutant levels at the sites. The leaves of A. scholaris and C. siamea growing along the busy roads of the city showed significantly higher concentration of Pb and Cd. The concentration of Pb and Cd in leaves was found quite high at M.A. Jinnah road as compared to Shahrah-e-Faisal, Nazimabad, Gulshan-e-Iqbal and Karachi University Campus. Higher level of Pb and Cd in leaves of A. scholaris might be due microrugosity of its surface area that is available for exposure to any pollutant. Low vehicular traffic activities at the campus showed lowest Pb and Cd contents in leaves of both the species. A comparison of leaf analyses gave a reasonably reliable measure of the total aerial fallout of heavy metals at the study area. The highest pollution levels of Pb (95 mg kg-1) and Cd (2.96 mg kg-1) was found in samples of A. scholaris at M.A. Jinnah road. Similarly, C. siamea also showed high levels of lead (89 mg kg-1) and cadmium (1.76 mg kg-1) at the same point. In this study, A. scholaris was found a useful biomonitor of Pb and Cd as compared to C. siamea