Heavy metal scavenging capacity of Mentha spicata and Allium cepa

The use of specially selected and engineered metal accumulating plants for environmental cleanup is an emerging frontline technology called ‘phytoremediation’ which describes a system wherein plants in association with soil organisms can remove or transform contaminants into harmless and often valuable form. During the present study the solid sludge and plants were collected from seven Sewage Treatment Plants (STPs) viz. Howrah, Garulia, Bhatpara, Nabadwip, Srirampur, Kona, Chandannager, and from the Periurban areas viz. Nadia/Chakdaha/Ektapur (N/C/E), Pumlia (N/C/P), Sikarpur (N/C/S), Tatla (N/C/T). Around 6–10 individual samples were mixed together and one average sample was compiled for analysis. Comparative study of heavy metals concentration in the roots and shoots of Pudina (Mentha spicata) and Onion (Allium cepa) showed their high heavy metals scavenging capacity. The concentration of Cd, Pb, Cr, and Ni in the roots of pudina (Mentha spicata) and Allium cepa (onion), at STP ranged from 0.833 to 1.88, 6.84 to 7.96, 25.3 to 21.56, and <0.05 mg kg⁻¹, respectively. The concentration of Cd, Pb, Cr, and Ni in the shoots of plants at STPs ranged from 0.43 to 1.96, 6.20 to 32.6, 26.7 to 24.43, and <0.05 mg kg⁻¹, respectively. Therefore, above-mentioned plant species may be selected according to their scavenging capacity for heavy metals from soils and sludges.