Effects of Zinc, a heavy metal, and Diazinon, a common pesticide, on the Embryonic Development of the
African Clawed Frog Xenopus laevis

Brett C. De Poister Fleetwood, Pennsylvania

Abstract

A dramatic decrease of amphibian populations had occurred within the past few decades. Anurans have been classified as bio-indicators, therefore, the disappearance of frogs from any habitat signals ecological crisis and it is important to focus on their development in the environment. Since little research has been done on the effects of pollutants on the embryonic development of anuran embryos, this project was developed to study the effects of zinc and diazinon, a common organic pollutant, on Xenopus laevis embryos by using histological techniques.

Testing required the use of embryos from stage 9 to stage 33/34. No embryos were allowed to develop past stage 35/36 (two days after fertilization).

Embryos were divided into 5 groups: the control, two different concentrations of zinc, and two different concentrations of diazinon. The concentrations of zinc and diazinon were extremely low and are lower than the LD50 as evidence by the fact that not one of the embryos died prior to being preserved for histological analysis.

As the embryos developed, 10 embryos were removed from every fourth stage. These embryos were then fixed, dehydrated, infiltrated, embedded in JB-4, then sectioned, stained, and analyzed.

It was concluded that the pollutants, zinc and diazonin, caused problems during late gastrulation. These problems led into a domino effect of abnormalities occurring in embryos during neurulation and later into organogenesis. The abnormalities that occurred during gastrulation were poor organization of the ectoderm, mesoderm, and endoderm. In the embryos undergoing neurulation, the neural plate and axial structures were poorly formed. The embryos undergoing organogenesis had poorly organized anterior and posterior ends.

By recognizing the importance of saving frogs and acting to stop environmental contamination, we can save other species, including ourselves.

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