水質汚濁斃死魚の死因判定法について-XII

Abstract

An attempt was made to detect mercury in the body of fish killed by inorganic mercury in solution (HgCl2). The total mercury was determined by the Dithizone-Carbontetrachloride method. The 48 hour median tolerance limit of HgCl2 for gold-fish (Carassius auratus) lay between 1-0.5 ppm Hg and 5 ppm Hg was found to be fatal to gold-fish in about 10 hours (Table 1). Mercury content of control fish ranged 0.14-0.36γ/g Hg. The bodies of fish killed by various concentrations of HgC12 showed values higher than 2.3γ/g Hg, while those living in 0.5 ppm Hg solution for 48 hours showed 1.2-1.8γ/g Hg. Gold-fish died in 0.5 ppm Hg solution within 6 or 7 days, and 2.3-4.6γ/g Hg was detected from the dead fish. When the body of fish killed by mercury poisoning was washed with running tap water for 24 hours after death, the mercury content of the body decreased to about 18.2-50.7% (Table 2). The distribution of mercury in seven parts of fish body was examined in two cases. In the 1st case, fish was killed by Hg in solution, and in the 2nd case, fish was soaked in Hg solution after death from suffocation. In the former, gill always showed the highest value and kidney came next (Table 3). In the latter, however, mercury content showed low values in every part examined. It is interesting to note that mercury was scarcely detected in spleen and kidney in the latter case. Some species of aquatic animals in the Abukuma and the Hirose-Natori Rivers were tested for mercury content to find the distribution of mercury in the natural aquatic environment (Table 6). The maximum value of mercury content was 3.72γ/g Hg in Zacco platypus. Almost all species, however, showed values lower than 1γ/g Hg. This means that there was no possibility of mercury pollution in both rivers.