Effect of temperature on cadmium and zinc uptake by the midge larvae Chironomus riparius

The effect of temperature (5 to 25 degrees C) was studied on the uptake of cadmium and zinc by larvae of the midge Chironomus riparius, using artificial chemically defined solutions. The influence of prior acclimation of midge larvae at five temperatures on metal uptake was examined. At all acclimation temperatures metal uptake in organisms increased with increasing exposure temperature. Among the different temperature exposure groups the effect of temperature acclimation on metal uptake is rather variable and a general pattern can not be distinguished. The integration of the different temperature effects explains 69% of the total variation in cadmium uptake and 68% of the total variation in zinc uptake by midge larvae. The factor that accounts for respiration explained 59% of the cadmium uptake and 60% of the zinc uptake by midge larvae. The apparent activation energies for larval metal uptake are much higher than the activation energy for the free diffusion of the cadmium or zinc ion but close to the activation energy for respiration, showing that metal uptake by midge larvae is largely controlled by active physiological rather than by passive diffusional processes.