¹ Hazardous Substance Division, National Institute of Agricultural Science and Technology, Suwon 441–707, Republic of Korea
²Plant pathology Division, National Institute of Agricultural Science and Technology, Suwon 441–707, Republic of Korea
³Department of Agricultural Chemistry, Chungbuk National University, Cheongju 361–763, Republic of Korea
⁴Department of Agricultural Biotechnology, Seoul National University, Seoul 151–921, Republic of Korea

*Corresponding author: yjahn@snu.ac.kr

Abstract

   This study was conducted to examine the toxic effects of paraquat on Daphnia magna and its behavior of paraquat in Korean agricultural conditions. Acute immobilization toxicity test on D. magna was performed for 48h at three different exposure systems such as water-alone (System A), water-sediment system (System B), and an equilibrated water-sediment system (System C). The concentration of paraquat in the System A was very stable over 48 h and the EC₅₀ was 6.39 ppm. In contrast, the concentration of paraquat in water phase of the System B was drastically decreased. The dissipation time in water (DT50) in the System B was ranged from 5.45 h to 13.05 h, while the EC₅₀ increased 3 times to 20.8 ppm. The concentration of paraquat in the water phase of the System C decreased over 90%, and no adverse effect was observed at 80 ppm. Considering that the toxicity of paraquat greatly decreased in the System B, there was large margin between predicted environmental concentration (PEC) and the concentration that would cause adverse effect on D. magna in environmentally relevant conditions. This study clearly indicated that paraquat equilibrated in the water sediment system practically did not acutely affect D. magna dwelling in the aquatic ecosystems, including rice paddy of Korea.