Abstract

Within the framework of the project "Evaluation of decontaminated soil", the applicability of bioassays with earthworms and plants for the quality assessment of decontaminated soil is investigated. In the final phase of this project, bioassays with earthworms and plants (radish, lettuce) developed earlier, were applied to a number of polluted and decontaminated soils. As earlier studies demonstrated that bioavailability of metals increased due to clean-up operations, the decontaminated soils were inriched with some organic matter (compost) and incubated for some months. Finally, the Microtox-test was applied to all soils. The results show, that concentrations of the metals As, Cd, Cu, Pb and Zn in the test organisms were lower on decontaminated soil compared to polluted soil. Also the results of the Microtox-test showed a reduction of the toxicity for most decontaminated soils. Addition of compost to the soils led to a further quality improvement, as was demonstrated both by lower metal concentrations in the tests organisms and by the results of the Microtox-test. On these enriched soils, however, growth of lettuce appeared to be severely inhibited; this cannot be explained. In most cases the metal concentrations in earthworms and plants cultured on polluted soils exceeded the "normal" values, which were established on the basis of bioassays in relatively unpolluted soils. Sometimes, this was also the case on decontamintated soil; not the enriched soils. Bioavailability of metals, expressed as the concentration factor, appeared to increase due to soil clean-up, but decreased again in the enriched decontaminated soils. This confirms results of earlier studies.