Developmental toxicity, uptake and distribution of sodium chromate assayed by frog embryo teratogenesis assay-Xenopus(FETAX)

The embryotoxicity and teratogenicity of Cr(VI) on the survival and morphology of the anuran Xenopus laevis have been assessed by frog embryo teratogenesis assay-Xenopus (FETAX). The lethal median (LC(50)) and teratogenic median (TC(50)) concentration values of Cr(VI) were 890 microM and 260 microM, respectively. The calculated teratogenic index (TI) value was 3.42, suggesting that hexavalent chromium has a teratogenic potential. Malformations of embryos included lifting of the body, coiling of the tail and body oedema. Furthermore, the chromium salt caused significant growth retardation at 25 microM exposure concentrations. The use of radiolabelled (51)Cr(VI) allowed the determination of the time course uptake of Cr in Xenopus exposed to concentrations ranging from 0.025 to 500 microM. The evaluation of its distribution into the body (head-abdomen-tail) was evaluated at different exposure times. Chromium is taken up at 24 h by Xenopus embryos for all concentrations tested. At 48 h post fertilization (stage of larva) the amount of Cr accumulated by the two-day-old larva ranged from 0.42 to 580 pg mg(-1) wet weight at 0.025 and 500 microM respectively. These amounts were lower than those at 24 h (2.77 to 11016 pg mg(-1) wet weight embryo) reaching values of the same order of magnitude at 120 h (five-days-old larva). Since at 48 h Xenopus development leads to a swimming embryo, the observed uptake at 24 h could be the result of the binding of Cr to jelly coat compounds surrounding the embryo body as confirmed by gel filtration experiments on (51)Cr-jelly coat. The interaction of Cr with jelly coat is in agreement with the role of jelly coat in protecting the embryo against pathogen and chemical toxins to ensure fertilization. This work further supports the hypothesis that Cr contamination of surface waters could contribute to explain the reported worldwide depletion of frog population