Enhancement of phytoremediation efficiency of Acacia mangium using earthworms in metal-contaminated soil in Bonoua, Ivory Coast

In this paper, the impact of Pontoscolex corethrurus on Acacia mangium growth and its phytoremediation efficiency in metal-contaminated soils were studied in a greenhouse pot culture under four treatments: non contaminated soil-non inoculated, control (C); non contaminated soil-inoculated (NcI); contaminated soil-non inoculated (CNi); contaminated soil-inoculated (CI). The results showed that A. mangium growth performance and its Pb, Ni and Cr uptake were significantly (P<0.05) increased under CI treatment. Under CNi treatment, A. mangium uptake more Ni and Cr content in root tissue than in shoot tissue. But for Pb, the greater content was noted in shoot tissue. A. mangium non-inoculated preferentially promoted the phytoimmobilization process for Cr and Ni and the phytoextraction process for Pb. However, under CI treatment, the greater content of potential toxic elements (Cr, Ni and Pb) was observed in roots tissue and A. mangium inoculated promoted the phytoimmobilization process for Cr, Ni and Pb. In addition, the phytoextraction efficiency (PEE) of A. mangium increase (ranged 0.1% under CNi to 14% under CI treatment. This study indicates that earthworms can be used to enhance the phytoremediation efficiency of metal-tolerant plant species in contaminated soil.   Key words : Acacia, heavy metal, phytoextraction, potential toxic element, Pontoscolex corethrurus, inoculation.