Effect of water hardness on the toxicity of cadmium to the green alga Pseudokirchneriella subcapitata in an artificial growth medium and nutrient-spiked natural lake waters.

The effect of cadmium (Cd) on the growth rate of the green alga Pseudokirchneriella subcapitata was investigated at three different levels of water hardness in an artificial growth medium and in three nutrient spiked, Norwegian natural soft lake waters. The lake water with the lowest levels of hardness and dissolved organic carbon (DOC) (Lake Byglandsfjorden) showed the highest toxicity attributed to Cd. In water from this lake without addition of calcium and artificial chelators, the EC50 for inhibition of growth rate was 9.4 microg Cd/L and EC10 was 2.8 microg Cd/L. When the hardness of the waters was increased by addition of calcium the adverse effects of Cd were in general reduced. In all tested media, the concentration/effect slope was reduced with increasing hardness. This led to a higher effect of hardness on EC50 than EC10.