The combined use of electrokinetic remediation and phytoremediation to decontaminate metal-polluted soils: a laboratory-scale feasibility study.

The use of a combination of electrokinetic remediation and phytoremediation to decontaminate two metal-polluted soils has been demonstrated in laboratory-scale reactors. One soil was heavily contaminated with copper, the other with cadmium and arsenic (2500 microg g(-1) Cu; 300-400 microg g(-1) Cd and 230 microg g(-1) As, respectively). Test reactors with two separated chambers, each with a capacity of 5.25 kg soil, were constructed, then the respective chambers were filled with either a mixture of the polluted soil and a control topsoil (75:25) or topsoil alone. Reactors were sown with perennial ryegrass (Lolium perenne cv Elka) and a constant voltage of 30 V was applied continually across the soils in each reactor. Soil sampling took place at the start and the end of the test run, whilst plant foliage was sampled after approximately 3 weeks (both reactors) 6 weeks (Cd soil reactor only) and at the conclusion of each test run (98 days Cu soil, 80 days Cd soil). Soil and plant metal concentrations were measured, together with soil pH. Results showed that in both soils there was a significant re-distribution of metals from anode to cathode in the test reactors, coupled with an enhancement of plant Cu uptake in the cathode region for the Cu soil. Patterns of plant Cd uptake were less clear cut and were not as clearly related to the redistribution of Cd measured in the soil. There was significant acidification of soil at the anode in each test reactor, but soil pH in other parts of the reactor changed little during the course of the experiment. Plant growth was affected at the anode, but was not affected in other parts of the reactor. There was no visual evidence of metal toxicity in the ryegrass in either polluted soil. Some effects on soil fungi were apparent, with a stimulation of Fusarium infection of ryegrass in the cathode region of all reactors and the appearance of sporophores of Coprinus in the same location. It is concluded that the combination of the two techniques represents a very promising approach to the decontamination of metal polluted soils that now requires validation in field conditions.