BIOAVAILABILITY AND ECOLOGICAL EFFECTS OF CADMIUM ON FOLSOMIA-CANDIDA(WILLEM) IN AN ARTIFICIAL SOIL SUBSTRATE AS INFLUENCED BY PH AND ORGANIC-MATTER

The validity of the pore-water hypothesis was studied by determining t he bioavailability and toxicity of cadmium to the collembolan species Folsomia candida, in artificial soils with different pH and different organic matter content. Cadmium solubility, cadmium accumulation by in dividuals and effects on survival, growth and population-increase were determined. Water soluble cadmium concentrations, at comparable total soil concentrations, increased with decreasing pH and decreasing orga nic matter content of the soil. No consistent pattern in accumulation of cadmium by Collembola was found for the different treatments. The v ariation in LC50 values and EC50 values for growth and population incr ease, increased when effects were expressed as soluble concentrations instead of total concentrations in the soil. When expressed as interna l concentrations the variation decreased except for population increas e at different pHs. It may, therefore, be concluded that the bioavaila bility of cadmium to F. candida is not predicted by the water soluble concentration and that collembolan sensitivity is not only determined by the internal cadmium concentration but also by differences in soil characteristics. This hampers a straight-forward prediction of metal t oxicity using the pore-water hypothesis.