An outbreak of copper poisoning in Mute swans (Cygnus olor)

Eight of 9 Mute swans (Cygnus olor) untied in the river acrossing the central part of Tottori-city died within the period of 40 days of summer in 1989. Seven of 8 Mute swans were pathologically examined. In all swans many yellowish-brown to greenish-brown granules were found in the cytoplasm of hepatocytes. The granules were intensely stained with rhodanine copper stain, schmorl method, and Berlin blue stain. Ultrastructurally, many lysosomes increased in size and density in the cytoplasm of hepatocytes. Other three swans, that died at other places, were served as controls. In control swans, many brown granules intensely stained with schmorl method and Berlin blue stain were also found in hepatocytes, but the number of rhodanine-positive granules were fewer than those of the affected cases. X-ray qualitative analysis showed three peaks corresponding to copper, zinc and sodium in the liver of the affected and control swans. Quantitative analysis demonstrated that mean hepatic copper concentration of the affected group was significantly higher than that of control group (P less than 0.01). From these findings, we concluded that all of 7 Mute swans died of copper poisoning.