1. Laboratory of Toxicology, Graduate School of Veterinary Medicine, Hokkaido University, Kita18, Nishi9, Kita-ku, Sapporo, Hokkaido 060-0818, Japan
2. Water Research Group, Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom, 2520, South Africa
3. Graduate School of Veterinary Medicine, Hokkaido University, Kita18, Nishi9, Kita-ku, Sapporo, Hokkaido 060-0818, Japan