Report II Comparison of the mercury compound in the shellfish from Minamata Bay with various mercury compounds experimentally accumulated in the control shellfish

Abstract

In order to investigate the genesis of the poison in the fish and shellfish from Minamata Bay biological and chemical properties were compared with mercury compounds experimentally accumulated in the control shellfish.1) The mercury content in the shellfish Hormomya mutabilis (Gould) showed ca 100 ppm of dry weight at the end of 1959, but afterwards it decreased gradually and showed 30 ppm in August of 1960, probably on account of the completion of the waste treatment equipment of Minamata Factory. But in January of 1961, it increased again and showed 50 ppm, perhaps owing to the transitory suspension of the operation of the waste treatment.2) Toxicity of mercury compounds to the short necked clam-Venus japonica (Deshayes) was observed. Venus could survive for about 1 week in the sea water containing mercury compounds at the rate of 0.3 ppm as Hg, and the mercury content in Venus showed ca 40-50 ppm of dry weight. Na2S2O3 suppressed the toxicity of mercury compounds, but Ca-EDTA had no effect on it. The mercury content in Venus depended generally on the surviving period and not on the toxicity, but the accumulation of mercury in Venus cultured in the sea water containing alkyl mercury compounds had a tendency to be greater than that of other mercury compounds.3) The mercury content in organs of the shellfish from Minamata Bay was higher in the nervous nodules than in other organs. But the mercury content in organs of the shellfish cultured in the sea water containing HgCl2 was higher in the gills than in other organs.4) The shellfish Venus cultured in the sea water containing HgCl2 was administered to rats and mice. The distribution of mercury in organs of these animals had the higher content in the kidney and the liver.5) The shellfish cultured in the sea water containing inorganic and organic mercury compounds were digested with pepsin at pH 1.6 and the digests were distilled with steam and the mercury in the digested fluids and that transferred into distillates were observed. Mercury was found in digested fluids and distillates of the shellfish which was accumulated with alkyl mercury compounds, especially with methyl mercury and ethyl mercury, but not with other organic and inorganic mercury compounds.6) These results suggest that organic mercury compound accumulated in the shellfish has come directly from the sea water, and has not been synthesized from inorganic mercury compounds in the shellfish. And from results of the digestion and the steam distillation of the control shellfish cultured in the sea water containing many inorganic and organic mercury compounds, the organic mercury in the shellfish from Minamata Bay was supposed to be an alkylmercury compound, probably methyl or ethyl mercury compound.