Biological monitoring to detect both water pollution and water quality recovery based on valve movements of freshwater bivalves (Corbicula japonica)

The valve movement pattern of the freshwater bivalve Corbicula japonica (C. japonica) following exposure to test chemicals was monitored. We conducted the exposure test with two heavy metal compounds, cadmium chloride (CdCl ₂; 0, 0.1, 1, or 10 mg/L) and copper (II) chloride (CuCl₂; 0, 0.1, 1, or 10 mg/L) in a continuous flow system. After a pre-exposure period in a test chamber, which was filled with dechlorinated tap water for 1 h, the bivalves were exposed to the test chemicals for 3 h. After that, only dechlorinated tap water was released again into the test chamber for 2 h. Thus, the valve movements were continuously recorded for a total of 6 h. On exposure to CdCl₂ (1 and 10 mg/L), the valve movement of C. japonica closed. However, the valve movements of C. japonica in all CdCl₂ groups recovered after termination of the exposure. C. japonica showed decreased distance between the valves on exposure to CuC₂ (0.1,1, and 10 mg/L). However, C. japonica restarted their valve movements only in the recovery period at 0.1 mg/L CuCl₂. Therefore, we conclude that real-time monitoring of the valve movement of C. japonica is a useful method to detect both the contamination with a toxicant and recovery of the water quality in an aquatic ecosystem. In addition, it can be used for the assurance of the water quality.