The use of the integrated soil microcosms to assess accumulation of caesium (Cs) and lead (Pb) from contaminated soils by earthworms (Eisenia andrei) and the sunflower (Helianthus annuus)

Heavy metal and radionuclide contamination in soils is a serious problem and increasing. Lead is one of the most consistent pollutants in soil; while cesium is commonly released in radioactive wastes and has contaminated large land areas. Phytoremediation can be used to decontaminate soils by removing heavy metals (Cu, Ni, Pb, and Zn) and radionuclides (90Sr, 137Cs, 234U). In this study we used the earthworm Eisenia andrei and sunflower dwarf sensation (Helianthus annuus) as tools to assess the accumulation of stable Cs and Pb individually and in combination. The efficacy of this remediation was evaluated using integrated soil microcosms with soil contaminated with Cs alone at 25 and 250 ppm; Pb alone (1500 ppm) and Pb (1500 ppm) together with Cs (250 ppm) in the laboratory. Results revealed that the sunflower bioaccumulated Cs and Pb and accumulation was more in roots than in the shoots. The Cs bioaccumulated in plants and earthworms increased with higher Cs in soils. The presence of earthworms did not increase Cs and Pb accumulation or the transfer of the trace metals from roots to shoots. The presence of Cs+Pb as a mixture reduced the accumulation, transfer and the translocation of Cs and Pb. Earthworms had a high tolerance for Cs and Pb and accumulated Cs (250 ppm) and Pb (1500 ppm). It was also evident that Pb in earthworms in the top layer of the soil core was higher than in the lower core. The presence of Pb with Cs as a mixture reduced accumulation of Pb and Cs in earthworms. Lead removal from soil was only 0.9 to 5.5% while Cs was removed to a greater extent, i.e.27 to 49%. Lead and cesium were also detected in leachates at very low levels. The study also demonstrated that Pb in soil was less mobile and less bioavailable than Cs.