Developmental impact of atrazine on metamorphing Xenopus laevis as revealed by nuclear analysis and morphology

Atrazine is one of the major surface water contaminants in the midwestern United States. Speculations have arisen on the potential effects of atrazine contamination to anuran larvae developing in these surface waters. In this study, Xenopus laevis tadpoles were exposed to environmentally relevant concentrations of atrazine. Nuclear and morphological endpoints were used to assess the effects of atrazine on developing X. laevis. Atrazine significantly affected metamorphing X. laevis after three-weeks exposure compared to controls as revealed by flow cytometric nuclear DNA analysis. The flow cytometric analysis was reflective of developmental effects. The number of nuclei per organism also was analyzed. Nuclei number was found to be associated with X. laevis development. Nuclei counting showed significant effects of atrazine after five-weeks exposure. A third endpoint, Nieuwkoop and Faber (NF) morphological staging, also demonstrated that atrazine significantly affected development after four weeks. Atrazine was found to alter the timing of metamorphosis of X. laevis using both nuclear analysis and gross morphology. The NF staging was found to be a sensitive assay to measure effects of development, whereas flow cytometry provided an impartial quantitative measure.