RP8 Ecotoxicology of Agrochemicals and Pharmaceuticals
Thursday, 17 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall
(HOW-1117-745086) Chronic effects of atrazine on the development of Northern Leopard Frog (Rana pipiens) tadpoles.
Fridgen, C1, Pauli, B2, Berrill, M1, Doe, K3, Jackman, P3, 1 Department of Biology, Trent University, Peterborough, Ontario, Canada2 Canadian Wildlife Service, Ottawa, Ontario, Canada3 Environment Canada, Moncton, New Brunswick, Canada
ABSTRACT- Amphibians are an excellent model organism in which to observe chronic effects of contaminants, in particular effects on the thyroid and gonadal axes, because of their endocrine-mediated differentiation processes including metamorphosis and gonadal development. Atrazine exposure has been associated with abnormal development of exposed frogs, particularly demasculinization and feminization, through a possible mechanism of induced aromatase activity levels increasing conversion of androgens to estrogens. We conducted a blinded study examining the effects of chronic atrazine exposure (0.1 and 1.8 
g a.i./L as Aatrex Liquid 480) on the development of Northern Leopard Frog (Rana pipiens) tadpoles. Animals were exposed from the egg stage to metamorphosis. Our main objectives were to compare our results with existing data, provide information concerning sensitive stages and endpoints in Ranid amphibians, and investigate new histological methods to quantify and stage early gonad differentiation in R. pipiens. Atrazine exposure caused significant chronic effects on both the growth and development of tadpoles and their gonads at concentrations as low as 0.1 g/L. Preliminary statistical analyses indicate that Gosner Stage 25 to 40 tadpoles exposed to the lowest concentration tested have significantly increased body length and mass, as well as an increased average stage of development over time, yet significantly fewer tadpoles being reared in both test concentrations reached metamorphic climax at test termination. Both atrazine treatments induced significantly larger female gonads, increasing both the ovary length and area. In addition, preliminary histology has revealed signs of intersex, testes with large primary oocytes, and ovaries with areas of abnormal somatic tissue. Further in-depth histological analysis of gonads to examine the influence of atrazine exposure on oocyte size, gonadal differentiation rate and stages, as well as intersex incidence is being conducted.
Key words: amphibians, atrazine, gonads, pesticides