Low level treatments of amphibian embryos with Cadmium: beneficial and adverse effects according to exposure conditions

LUIS ALFREDO CASTAÑAGA; CAROLINA DORA GONZÁLEZ EIRAS; CAROLINA MARIEL ARONZON; CRISTINA SILVIA PÉREZ-COLL; JORGE HERKOVITS

Mérida México

Congreso; Ecología en una era de globalización; 2006

Society of the Americas (ESA)

>Due to the high toxicity of cadmium it causes great concern for environment and human health protection purposes. Amphibians are considered endangered species and their embryos were used successfully for hazard and risk assessment for surface water quality as well as for acclimation studies. The main purpose of this contribution is to report the effects of a wide range of low-level Cadmium exposures, including pristine surface water conditions, on native amphibian embryos from South America, by means of challenge treatments of the experimental embryos to lethal concentrations of this heavy metal. Duplicate groups of 100 Bufo arenarum embryos at complete operculum stage (S25) were treated up till 11 days with Cd in a range of concentrations between 0.01 and 12.5 ug/l in AMPHITOX solution (in pristine surface water Cd concentrations range between 0.001-0.013 ug/L). Two protocols were conducted: i) constant exposure condition and ii) a gradual increase in Cd concentrations. 10 embryos by triplicate from each experimental group were challenged after 5 days of treatment to 0.12mgCd2+/L and 6 days later to 0.16mgCd2+/L (LC100/24hr obtained at 5 and 11 days respectively). Control conditions were conducted. Lethality was registered 6, 9, 12, 24 and 48hr post challenge resulting at 9 hr as an average of 20% more lethality compared with controls in all low level exposure except the two higher conditions in which a significant increase in the surviving embryos was registered (100%) while after 11 days of low level exposure the beneficial effect was expanded to all conditions. The results allow to conclude that amphibian embryos register Cd concentrations even in pristine conditions. It seems to be a balance between concentration and time of exposure versus adverse or beneficial effects. For short exposure periods a slight adverse effect could result in case of the lower concentrations of Cd while the beneficial effect is limited to the higher exposure condition. Conversely, by expanding the exposure time the beneficial effect is expanded to all conditions. It is noteworthy that amphibian embryos could respond even to Cd concentration found in pristine environmental conditions as well as to different sub toxic exposures to this heavy metal, a scenario that seems to be very frequent in present environmental conditions