Effects of multiple routes of cadmium exposure on the hibernation success of the American toad (Bufo americanus)

The effects of multiple routes of cadmium exposure on juvenile American toads (Bufo americanus) were evaluated using environmentally relevant concentrations. During or after exposure, toads were individually hibernated for 172 days at approximately 4 degreesC. The following experiments were conducted: 1) dermal exposure (hibernation in soil contaminated with up to 120 mug Cd/g (dry weight)); (2) injection exposure (single injection with cadmium to achieve a maximum whole-body nominal concentration of 3 mug Cd/g (wet weight) 12 days before hibernation in uncontaminated soil); and, (3) oral exposure (feeding with mealworms containing less than or equal to16 mug Cd/g (dry weight) for 50 days before hibernation in uncontaminated soil). We hypothesized that sublethal levels of cadmium would become lethal during hibernation because of combined chemical and cold stress. No prehibernation mortality occurred in the injection and oral exposure studies. There was a significant treatment effect on whole-body cadmium concentration in toads orally or dermally exposed and on percent of cadmium retention in toads orally exposed. There was also a trend of increased time-to-burrowing and more toads partially buried with greater cadmium concentration in the dermal study, which indicated avoidance. In all 3 experiments, no significant differences were found among cadmium treatments in hibernation survival, percent of mass loss, or locomotor performance. However, toads fed mealworms averaging 4.7 mug Cd/g (dry weight) had only 56% survival compared with 100% survival for controls. Although our results suggest that environmentally relevant levels of cadmium do not pose a great risk to American toads, factors such as soil type or prey species may increase cadmium bioavailability, and other amphibian species may be more sensitive to cadmium than B. americanus.