ABSTRACT
Cadmium is one of the most troublesome toxic heavy metals. It accumulates in the water reservoirs and agricultural soil as a result of intensive use of Cd contaminated phosphate fertilizers, e.g. in agriculture in the North Central Province (NCP) of Sri Lanka. The hyper-accumulator Thlaspi caerulescens, accumulates up to 1000 ppm Cd in shoots without exhibiting toxicity symptoms. The storage rhizomes of year old Nelumbo nucifera (lotus) natural vegetation in water reservoirs in NCP accumulated 253+/-12 mg Cd/kg. Seedlings of lotus grown in 5% Hoagland's solution at 0.75, 1.0 and 1.25 ppm cadmium sulphate showed a significant increase in Cd removal of 0.0334-0.121 ppm/week. However the removal rate of Cd from water failed to increase any further at higher concentrations of Cd in water. The slow growth rate and low rate of phytoextraction demands a more effective but an affordable method of remediation in order to combat the prevailing elevated cadmium levels in NCP that causes chronic renal failure (CRF). We have developed a large scale filtering device using rice husk. We have achieved successful results in sequestering Cd using raw rice husk as well as amorphous silica derived from rice husk.
