The use of Chromolaena odorata (L) King H.E. Robins for the treatment of soil contaminated with metals and crude oil under green house conditions

摘要

Pot experiments were used to investigate the capability of Chromolaena odorata (L) to grow in different concentrations of three heavy metals in crude oil-contaminated soil and to estimate its capability to remediate the contaminated soil. Chromolaena odorata propagated from stem cuttings were transplanted into contaminated soil containing 50000 mg kg~(-1) crude oil and between 100 and 2000 mg kg~(-1) of cadmium, nickel and zinc. The plants were watered weekly with water containing 5% NPK fertilizer for 180 days. Chromolaena odorata did not show any growth inhibition in 50000 mg kg~(-1) crude oil, as was shown in the control experiment, and in all concentrations of zinc. Plants in experiments containing 2000 mg kg~(-1) cadmium showed little adverse effect with smaller and paler leaves compared to those in zinc treated soil. Nickel showed more visible effects, with plants in 1000 and 2000 mg kg~(-1) experiments having much smaller and paler leaves, and less profuse branching. After 180 days reduction in heavy metals were: 100 mg kg~(-1) experiments, Zn (35%), Cd (33%) and Ni (23%); 500 mg kg~(-1) , Zn (37%), Cd (41%) and Ni (25%); 1000 mg kg~(-1) , Zn (65%), Cd (55%) Ni (44%); 2000 mg kg~(-1) , Zn (63%), Cd (62%) and Ni (47%). The concentrations of the heavy metals present in the plant tissues showed that the plant accumulated more of the Zn than Cd and Ni. The accumulation of Zn and Cd was highest in the 2000 mg kg~(-1) experiments and Ni in the 500 mg kg~(-1) experiments. Crude oil was reduce by 82% in the experiments that did not contain heavy metals and by between 74 and 80% in the heavy metal treated soil. The control experiments without Chromolaena showed a reduction of between 38 and 47% in crude oil concentration. This portion of the reduction was attributed to microbial action and natural attenuation. These results show that Chromolaena odorata (L) has the capability of thriving and phytoaccumulating heavy metals in contaminated soils while degrading the contaminant crude oil. It also shows that the plants capability to degrade crude oil in contaminated soil is not significantly affected by the concentrations of metals in the soil.