III. Effects of particular pollutants - Mercury pollution in Sweden with special reference to conditions in the water habitat

Abstract

The occurrence of mercury in water, air, etc., was observed 30 years ago by a German scientist. During the 1950s and 1960s, great attention was paid to the Hg problem in Japan and Sweden. In Sweden the whole environment was contaminated due to the widespread use of Hg in agriculture and industry. The organic Hg compounds of alkyl-type and aryl-type, which were used for 10 to 20 years as fungicides in agriculture and in the pulp industry, have had serious effects on animals in both terrestrial and aquatic environments. These two types of Hg compounds are now forbidden in Sweden. However, a new type of compound, alkoxyalkyl-type, may now be used as a fungicide in agriculture. Much Hg is discharged into the air and water due to industrial activities, e. g. the chlorine-alkali industry and many other activities such as the burning of waste products containing small amounts of Hg. Although most Hg is inorganic Hg or organic Hg in the form of phenyl-Hg (aryl-type) (discharged as industrial wastes), most of the Hg in fish from lakes and the Baltic in Sweden is present as methyl-Hg (alkyl-type). It has been demonstrated that methylation of Hg takes place due to bacterial and enzymic activity. High Hg contents in the wild fauna, grain-eating birds and their predators, gave the first scientific evidence that the terrestrial environment was contaminated. Since the ban on alkyl-Hg in agriculture was introduced the Hg concentrations in birds living in the terrestrial environment and of food such as eggs, pork, etc., produced on land, have dropped. Unfortunately this is not the case in the aquatic habitat. Although the discharge of Hg to water and air have been restricted in Sweden, the whole environment is so heavily contaminated that it will take a long time for the Hg concentrations to decrease. The most serious Hg problem in Sweden today is the high Hg concentration in fish. Fish from a certain number of lakes and from extensive coastal areas on the Swedish east and west coast are now forbidden for sale in Sweden. In general, water organisms or birds feeding in the water habitat have higher ‘natural’ contents of Hg than terrestrial wildlife. Pike has been chosen as an indicator organism of Hg contamination. Levels higher than 200 ng Hg/g are considered abnormal. Most of the investigated fishes from freshwater and coastal areas have concentrations in the range of 200 to 1000 ng Hg/g. Fish with more than 1000 ng Hg/g exceed the temporary limit of 1 mg Hg/kg (1000ng/g) now valid in Sweden. Earlier, FAO/WHO proposed a practical residue limit up to 0.05 mg Hg/kg (50 ng/g) for terrestrial food. The effects of Hg intake in man were first observed in Japan. During the years 1953 to 1960, 111 persons living around Minimata Bay, were killed or seriously disabled. They were poisoned by fish and shellfish with elevated Hg concentrations. In Sweden elevated Hg concentrations have been observed in blood corpuscles, blood plasma and hair of people eating very much freshwater fish, but also the people eating saltwater fish.