Thesis (M.Sc.)--Chulalongkorn University, 2011

Amphibians have declined dramatically in many areas around the world. Agrochemicals and chemicals contamination to the environment are also considered as a disastrous causes of amphibian declines. Atrazine, a triazine-herbicide is the most commonly used herbicide in the world and probably in Thailand. Atrazine is generally applied in rainy season when amphibians are congregating and preparing for the breeding. Therefore, frogs either in the agricultural fields or the adjacent wetlands could be exposed to atrazine. This study designed to determine the effects of atrazine on the embryonic and larval development in the rice field frog Hoplobatrachus rugulosus (Wiegmann, 1834), a common frog species in Thailand. The study was divided into 3 parts. The first part was to determine the normal embryonic and larval developmental of H. rugulosus to find out each time of developmental stage for the following experiments. The second part was to determine the effects of atrazine on early development of H. rugulosus. The early embryos at mid-blastula were treated with the ecologically relevant nominal concentrations i.e. 0.001, 0.01, 0.1, 10, 100, and 1,000 ppb using FETAX protocol for 96 hours. The result shown that the nominal concentrations of atrazine used in this experiment did not cause significant statistical effects (p<0.05) such as mortality rate, snout-vent length and developmental abnormalities, even though certain abnormalities i.e. tail flexure and abdominal edema were found in all treatment groups (except 0.01 ppb). The last part was to determine the effects of atrazine on gonad development and later developmental stages. The early embryos were treated with the nominal concentrations of atrazine i.e. 0.001, 0.01, 0.1, 10, 25, 100, and 1,000 ppb, respectively. The embryos were treated with atrazine until the animal completed metamorphosis. The results showed that the nominal concentrations of atrazine did not cause any effects to the metamorphosis and gonad development of H. rugulosus (p<0.05). In conclusion, it is suggested that pure atrazine at the ecologically relevant concentrations were not capable of causing direct effects to H. rugulosus development in laboratory condition.