Mortality and antioxidant responses in the planarian (Dugesia japonica) after exposure to copper.

The planarians (Dugesia japonica) are distributed widely in China, Japan, Korea, and southern Siberia. In this study, the acute toxicity of copper on D. japonica was evaluated using mortality and the activity of the enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), and reactive oxygen species (ROS) as endpoints. Acute toxicity tests were conducted according to the American Society for Testing and Materials guidelines. The 24-, 48-, 72-, and 96-h median lethal concentration that killed 50% of individuals (LC50) were calculated as 8.70, 6.31, 4.48, and 4.23 mg Cu²⁺/L, respectively, based on measured copper concentrations. When compared with different phyla or classes of freshwater animals, the rank of D. japonica in species sensitivity was in the range of 25-26 for 96-h LC₅₀. The antioxidant enzymes SOD and CAT were determined in D. japonica exposed to two copper concentrations (50 and 100 μg Cu²⁺/L) with a short-term exposure (15 days). They all attained peak value and then reduced during the experimental period. The GPx activities were activated only for 100 μg/L treatments at days 3 and 6 and then renewed to the original level. Meanwhile, copper significantly increased the levels of ROS in D. japonica. Our study suggests that the adult D. japonica was less sensitive to copper than most other aquatic species. Copper may induce oxidative stress and interfere with the antioxidant defense system of the D. japonica, including SOD and CAT. GPx might be an insusceptible antioxidant enzyme in the metabolic detoxification processes in adult D. japonica.