Combined effects of cadmium and ultraviolet radiation on mortality and mineral content in common frog {Rana temporaria) larvae

摘要

The combined effects of UV with Cd~(2+) exposure on the mortality and mineral content of common frog larvae was investigated. Tadpoles were raised in increasing concentrations of Cd~(2+) (0-2000 μg×L~(-1)). Additionally the larvae were exposed to biologically effective doses of UV-A (0.24 kJxm~(-2)) and UV-B (2.71 kJ×m~(-2)). Parallel groups were grown in the same ionic concentrations in the absence of UV. In the second experiment larvae were exposed to sublethal doses of Cd~(2+) (1000 μg×L~(-1)) for 3 days. Then the larvae were submitted to 4 weeks of recovery in clean water. Cd, Cu, Zn, Ca, Mg, Fe, Na, K contents and Na/K ratio were measured. In tadpoles exposed exclusively to Cd~(2+) the 96 h LC50 = 3155 μg×L~(-1). By contrast in tadpoles exposed to Cd~(2+) and UV for 96 hours the LC50 = 710 μg×L~(-1). More cadmium was accumulated in UV-exposed tadpoles. On the other hand tadpoles exposed to UV radiation removed cadmium more efficiently than non-irradiated larvae. Cu, Na, and K were positively correlated with Cd content while Mg was negatively correlated with Cd. Animals exposed to combined stressors had lower Mg, Fe, Ca, Na, Zn contents, lower Na/K ratio and higher Cu and K contents than animals exposed exclusively to cadmium. Our studies indicate that cadmium ions combined with UV significantly increase mortality of common frog tadpoles. This may be related to higher cadmium uptake, disturbances in the content of essential metals and ionic imbalance.