1. Laboratory of Toxicology, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, 18 W9, Kita-ku, Sapporo 060–0818, Japan
2. Diagnostic Center for Animal Health and Food Safety, Obihiro University of Agriculture and Veterinary Medicine, Obihiro 080–8555, Japan
3. Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa