日本ウナギに対するアンモニアの急性および漫性毒性

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The lethal effect and growth suppressing effect of ammonia on eel Anguilla japonica were examined. The 24h-LC50 of total ammonia nitrogen at 25°C was estimated to be 2844mg/l at pH5, 820mg/l at pH7 and 16.8mg/l at pH9. Estimated concentrations of unionized ammonia nitrogen in the culture media containing total ammonia nitrogen at the level of 24h-LC50 are almost constant (4.6-6.0mg/l) in the pH range from 7 to 9. This fact suggests that an unionized ammonia alone is responsible for the toxicity of ammonia in this pH range, however, in the range of pH from 5 to 7, estimated concentration of unionized ammonia decreased with decreasing pH. Thus, at the pH lower than 7, ionized ammonia must have shown toxicity for the eel together with unionized ammonia. In the chronic toxicity study at pH 6.8 for 9 weeks at 25°C, concentration of more than 0.067mg/l of unionized ammonia nitrogen suppressed the growth of eel significantly (P<0.05). The limit of safe concentration of unionized ammonia nitrogen for the growth of eel was estimated to be 0.034mg/l. Exposure of fish to unionized ammonia nitrogen for 9 weeks resulted in the increase of ery-throcyte number at the concentration of more than 0.067mg/l, and histological as well as pathological changes were observed in the gill tissue at the concentration of 0.121 and 0.228mg/l.
日本水産學會の論文