The effect of major cations on the toxicity of cadmium to Folsomia candida in a sand-solution medium analyzed by biotic ligand modeling.

The aim of this study was to assess the effect of major cations (Ca, Mg, Na, K, and H) on cadmium toxicity to the springtail Folsomia candida. Survival of the animals was determined after seven days exposure to different cadmium concentrations in an inert sand-solution medium, in different experimental setups with modification of the cation concentrations. Among the cations tested, Ca and Mg had protective effects on the toxicity of cadmium to the springtails while Na, K, and H showed less competition with free cadmium ions for binding to the uptake sites of the collembolans. Toxicity predicted with a biotic ligand model agreed well with the observed values. Calculated conditional binding constants and the fraction of biotic ligands occupied by cadmium to show 50% effects were similar to values reported in the literature. The results emphasize the important role of solution chemistry in determining metal toxicity to soil invertebrates.