The Minamata outbreaks point to the fact that it is possible for marine flora and fauna to pick up a toxic substance, and—in most instances-without killing the marine organism, pass this substance on to man with lethal effects.

The exact mechanism by which the process takes place and the metabolic effects of the transvector upon the primary toxic substance, or its precursor, is not understood, and constitutes an unexplored area of marine biotoxicology.

There is considerable evidence which points to the possibility that in certain types of marine bio-intoxications, certain marine bacteria may play a significant role in a toxin producing symbiotic relationship with marine algae."

MARINE WASTE-DISPOSAL AND POLLUTION IN THE MINAMATA BAY

The marine pollution in and outside of Minamata Bay was investigated by the author, as well as others and the results showed that the sea water was not appreciably contaminated by the factory disposal, no more than in other parts of Japan.

Marine waste disposal

The average discharge into the lagoon (precipitation basin) from the factory was 3700 m3/hr and the discharge from the municipal (urban) foul waste from Tazan river was about 600 m3/hr.

The fact that the dissolved oxygen control (DO) increases at the exit of the lagoon shows that the oxygen transfer in both the lagoon and the canal is effective (see Table 1).

TABLE 1.-WASTE DISPOSAL FROM THE FACTORY AND URBAN AREA TO MINAMATA BAY

Final discharge into the harbour, Hiyakken, of Minamata Bay was about 4300 m3/hr or more, but in the rainy season the disposal is diluted to a greater extent. A few typical values of DO, B.O.D., I, consumption and other chemical components are given in the following TABLES 1-2 and FIGS. 1-3.

TABLE 2. CHEMICAL ANALYSIS OF WASTE WATER AT THE EXIT OF THE "LAGOON"

Mercury contents in the factory disposal water and in sea water

Some people suspect that mercury is the cause of the Minamata disease. The author, however, has done extensive research in the effluent from the factory in and outside of Minamata Bay and also in other parts of Kyushu and Honshu (main island of Japan) and Hokkaido. Results are shown in the following TABLES 3-4 and FIGS. 4-6.

63-471 0-71—16

Note: The mercury contents in the sea water of southern parts of Kyushu, Honshu, and Kokkaido are shown in the table 4 and figs. 4-6 (map).

Deductions from our investigations showed that the mercury content at the exit of the factory lagoon was comparatively lower than that of disposal water of other factories where mercury was used as catalyst.

The results so far obtained can be summarized as follows:

(1) The sea water in and out of Minamata Bay has a sufficiently high value of dissolved oxygen (DO) and a small value of Biochemical Oxygen Demand (B.O.D.) and Chemical Oxygen Demand (C.O.D.) and, generally speaking, the degree of pollution here is nearly the same as on other bays of our country where an urban community or chemical plants are situated nearby.

The effluent from the Minamata chemical factory of Shin Nippon Chisso Hiryo Co. does not cause a remarkable effect on the pollution of the bay, compared with other similar cases in Japan.

(2) The concentration of mercury in sea water in this area is of the same order as in each of other bays of southern Kyushu. The concentration of mercury in the effluent from this factory is rather low compared with those from other factories manufacturing similar products.