Ecotoxicity assessment of Zn, Cu and Ni in contrasting soils using test organisms of different ecological niches
It was illustrated that Zn and Cu at or above 1000 and 800 mg kg-1 respectively were highly toxic to the earthworm studied. Cu was found to be more toxic to the earthworm than Zn in respect to mortality, growth and reproduction parameters in all three different types of soils. The body burdens of earthworms exposed to metal amended soils increased corresponding to the increased concentrations of amended metals irrespective of soils used. It was found that the BCFs in earthworms decreased with the increased concentrations of metals in soils. The higher BCFs is the indication of uptake of higher proportion metals from soil by earthworms. The highest BCFs was found for Ni followed by Zn and Cu indicated their bioavailability to earthworms. The growth (weight) of the earthworms was most affected by Cu. The combined toxicity of Zn:Ni, Zn:Cu and Cu:Ni to reproduction (cocoon production) of earthworms was mainly antagonistic and to some extent additive in both the Insch and Boyndie soils. Zn was more toxic than Cu to the nematodes as the number of nematodes decreased with the increase of metal amendments to soil. It was also found that the number of nematodes increased at the exposure to some lower doses of Cu and Ni. The joint toxicity of Zn:Ni, Zn:Cu and Cu:Ni on the number of nematodes was mainly antagonistic in both the Insch and Boyndie soils. In some cases the combined toxicity of metals to nematodes was not possible to assess because the threshold level was not reached and also due to irregular and inconsistent data. Cruden Bay soil was more vulnerable than Insch and Boyndie soils in evaluating the toxicity of metals to nematodes. Zn was found to be toxic for the lux-marked bacterial biosensor Escherichia coil HB101 pUCD607 and Pseudomonas fluorescens 10586r pUCD607 in different soils.