The effect of extreme waterborne cadmium exposure on the internal concentrations of cadmium, calcium, and sodium in Chironomus riparius larvae.

Chironomus riparius larvae (3rd-4th instar) were extremely resistant to waterborne Cd with 48h LC50s of 331 mg Cd/L in soft water (10 mg/L Ca CO(3)) and 1106 mg Cd/L in moderately hard (140 mg CaCO(3)/L) water. Unexposed larvae had whole body Ca and Na concentrations of 11.2(0.3) and 84.5(3.0) micromol/g, respectively. The larvae exposed through acute toxicity tests accumulated massive amounts of Cd, reaching >50 micromol/g in larvae exposed to 437 mg Cd/L, though burdens were lower at higher exposure concentrations. These Cd burdens were approximately fivefold greater than whole-body Ca concentrations. Cd exposure also had a significant negative effect on internal Ca: whole-body Ca declined by over 70% in larvae exposed to Cd above the LC50 concentration. The effect of Cd exposure on whole-body Na was much less dramatic as levels dropped by 10-28% in the acutely exposed larvae. Time series exposures (up to 72h) across a range of Cd concentrations (0.1-865 mg/L) revealed that internal Ca dropped within the first hour of exposure regardless of the concentration of Cd. In all but the highest (865 mg Cd/L) exposure, internal Ca eventually recovered to the control level. Cd resistance in C. riparius may lie in its ability to maintain internal Ca balance even when exposed to extreme (>100 mg/L) levels of Cd, coupled with remarkable capacities for storage-detoxification and excretion of Cd.