Lead pollution of Dhanmondi Lake in Dhaka

Dhanmondi Lake, which is located in densely populated central Dhaka, has been found to be heavily contaminated with lead. The average lead concentration in the lake water was found to vary from 151 to 210 μg/L during the dry period, and from 30 to 120 μg/L during the wet period. Increased rainfall and surface runoff appears to be responsible for reduced lead concentrations during the wet period. The lead concentration in the bottom sediment was found to vary from 10.7 to 44.7 mg/kg (dry weight), with sediment samples collected from locations in close proximity to major inlet points showing higher levels of contamination. The lead concentration in Dhanmondi Lake exceeds the values set for drinking, fishing, livestock, industrial and irrigation use in the environmental quality standards set out for Bangladesh. The determination of lead concentration in various parts of a fish of the Nilotica species revealed maximum bio-accumulation in the fins (4.90 mg/kg wet weight) and gills (4.78 mg/kg). Contaminated fish from the lake are becoming a local public health concern. Speciation calculations revealed that the major soluble lead species in Dhanmondi Lake are PbCO₃(aq), Pb²⁺ and PbOH⁺, with PbCO₃(aq) being the most dominant, while PbHCO₃⁺, PbCl⁺ and PbSO₄(aq) are minor species. Although the concentration of free ionic Pb²⁺, apparently the more toxic form, was found to be relatively low, any drop in pH would result in an increase in this species. With rapid industrialisation and an increasing number of motorised vehicles using leaded gasoline, lead pollution is likely to get worse unless appropriate remedial and regulatory measures are taken.