Abstract:
Rapidly increasing urban population is influencing the land use pattern causing enormous degradation to the surrounding environment. Land filling operations are being conducted in Dhaka city and many other urban areas by using dredged riverbed sediments for developing newly built urban zones. Being placed on the bank of Buriganga River, numerous development projects have been advanced using the Buriganga riverbed sediments. Huge volume of toxic waste is being discharged into Buriganga River from riverside industries without any treatment. Of all these chemical pollutants, heavy metals reaching soil maintain their presence in the pedosphere for many years, even after the removal of pollution sources. The newly developed areas containing heavy metal contaminated sediments may cause severe health hazards resulting from wind-blown dusts entering the respiratory system.
In this study heavy metal uptakes from contaminated Buriganga riverbed sediments by Indian mustard and Marigold plants, two locally available hyperaccumulators, were assessed. Initial characterization showed concentrations of chromium, lead, copper and zinc in the Buriganga sediments higher when compared to the toxicity reference values given for these heavy metals in soil for terrestrial plants, and soil invertebrate. The average background concentration of chromium, lead, copper, and zinc in the Buriganga riverbed sediments were found to be 141.5 mg/kg, 34.9 mg/kg, 38.7 mg/kg, and 287.5 mg/kg, respectively. It was observed that both Indian mustard and Marigold plants accumulated these heavy metals in different parts of the plant from the contaminated sediments and were able to maintain a growth rate of more than 90% compared to that in non-contaminated soil. The results indicated rapid phytoextraction of the heavy metals by the Indian mustard during its final growth phase, whereas rapid phytoextraction of the heavy metals was observed in case of Marigold in its initial growth phase. Total chromium, lead, copper, and zinc uptakes (in mg/kg of plant dry weight) by Indian mustard plant in 12 weeks were 102.6, 28.9, 53, and 1861.5, respectively. The uptakes (in mg/kg of plant dry weight) of the same heavy metals by Marigold plant in 12 weeks were found to be 112.3, 104.25, 82.5, and 716.75, respectively. Marigold showed higher uptake efficiency for chromium, lead, and copper; while Indian mustard was found to be more efficient in zinc uptake. Hence both of these plants can be used in an environment-friendly approach for treating heavy metal contaminated landfills developed using heavy metal contaminated riverbed sediments.
