Evaluation of the effects of atrazine exposure on Xenopus laevis in South Africa

Abstract

It has been reported that exposure of Xenopus laevis to atrazine in laboratory studies increase the incidence of intersex gonads and induced changes in plasma testosterone concentrations. However, the response to atrazine observed in laboratory tests with X. laevis has yet to be observed in exposed field populations. The aim of this was to ascertain whether exposure to atrazine and related triazines has caused endocrine responses in X. laevis under field and semi-natural microcosm conditions in South Africa. Corn is grown intensively in the north western part of South Africa. Atrazine concentrations in the experimental sites ranged from 1.5 - 11 .6 μg/L and in reference sites from 0.05 - 0.69 μg/L during the field use season. Starting in November 2001, weekly and later bi-weekly samples of water were taken to characterize exposure of X. /aevis populations to atrazine and related triazines. Tissue samples were taken from frogs for hormonal, gonadal, and aromatase activity. No gonadal abnormalities were observed in females. In male frogs a few frogs with only one testis were observed but no correlation was found between abnormalities and atrazine exposure. No hermaphrodite specimens were observed. A microcosm study with three replicates of atrazine concentrations 0, 1, 10 and 25 μg/L was designed. X. laevis tadpoles were exposed until completion of metamorphosis. 150 specimens per concentration were dissected. Based on gross morphology, no hermaphrodite specimens were observed. Deformed testes were observed but showed no dose response to atrazine. In reference ponds 4.00% of males had deformed testes. 1.335, 0.67% and 3.33% of males showed deformities at 1, 10 and 25 μg/L atrazine respectively. No deformed ovaries were observed in females. 214 specimens were randomly selected for histological examination and serially sectioned. Results obtained supported the findings of the gross morphology that gonadal anomalies showed no dose

response to atrazine. Histological examination revealed the percentage of individuals with gonadal anomalies to be 56.5% in the reference group, compared to the 56.7% in the 1 μg/L group, 58.8% in the 10 μg/L group, and 38.7% in the 25 μg/L group.