Environmental Contamination by Mercury (Hg Series No.13)

The author conducted the survey for mercury on the bottom mud and fish in the Oyabe River, as well as fish in other control and contaminated rivers in Japan.1. Total mercury content in the bottom mud of the Oyabe River was higher in the industrial area on the lower stream, than in the upper stream area.It may be attributed to previous contamination by waste water from factories.2. The results of three different surveys over a two year period (196869) revealed that the average level of total mercury in flesh of the Oyabe River's fish was 0.77ppm.The bottom-living Namazu (Catfish) showed the highest concentration among fish, i.e. 1.10ppm of total mercury and 0.66ppm of methylmercury.3. There was a considerable amount of mercury even in the fish of non-contaminated rivers, and the higher the total mercury concentration, the higher the level of organic mercury. Generally speaking the mercury level in river fish was higher than that of marine fish.4. Fish in the Hono River and the Shokotsu Rivers which are flowing in a mercury mine area showed particularly high levels of mercury.5. In fish of several rivers, ethyl mercury was also found, the Ugui (Dace) of the Jinzu River contained an extraordinary high level of ethyl-mercury.The cause of this contamination has as yet not been determined.