Phytoextraction of heavy metals in semi-aquatic environments using selected colocasia sp. and wedelia sp.

Abstract

This particular study focuses on remediation of heavy metal (Cd2+ and Pb2+) contaminated semi-aquatic environments using two plant species, a Colocasia sp. and a Wedelia sp. which are two common local plants growing under semiaquatic conditions. The main research work involved two experimental setups; the pot experimental setup and the hydroponic solution experimental setup (only for Colocasia sp.). In pot experimental setup a series of plants were allowed to grow for a certain period of time in pots containing varying concentrations of the analyte in soil. Then the plant materials (aerial parts and below ground parts separately) and the corresponding soil samples were digested and analyzed using flame atomic absorption spectrometer (FAAS). In hydroponic solution experimental setup, plants of similar nature were placed in conical flasks containing varying concentrations of the analyte in a hydroponic solution and observed for two weeks. Then the plant materials and the solutions were digested and analyzed using FAAS. The two experimental plants Wedelia sp. and Colocasia sp. have not proven to be suitable candidates for Cd2+ phytoextraction. The maximum tolerable Cd2+ concentration for Wedelia sp. was 450 mg per 1kg of dry soil while that for Pb2+ was 1500 mg kg-1 (after 60 days in soil). This shows that the toxicity of Cd2+ on the Wedelia sp. is higher than the Pb2+ toxicity on the same plant. At 450 mg kg-1 concentration in soil, phytoextracted concentration of Cd2+ was 8.1(±0.4) mg kg-1 while that for Pb2+ was 128.9(±4.6) mg kg-1. The maximum Cd2+ concentration which was tolerated by the Colocasia sp. was less than 10ppm and survived less than a week in hydroponic solution.