8 Global Contamination of the Oceans by Heavy Metals
8.1 How Much Mercury May Be Tolerated in Fish for Human
Consumption?
Mercury is dangerous for man, as was demonstrated with the casualties of Minamata
(see Chap. 3.2). The United Nations World Health Organization (WHO 1976a) summarized what was known about mercury poisoning and concluded that toxic effects
of mercury can be expected to become manifest in the most sensitive groups of
human adults when over longer periods of time a weekly intake of 1.3-2.9 mg
methylmercury takes place, equivalent 0.02-0.05 mg/kg body weight. Such mercury
intake results in blood concentrations of 0.2-0.5 mg/l and in hair concentrations of
50-125 mg/kg. Victims of the "Minamata Disease" had consumed, with polluted fish,
about 14 mg of mercury per week, and analyses of their blood and hair showed
respectively high mercury concentrations (Table 7). Concentrations of less than
0.02 mg/l in blood and less than 6 mg/kg in hair, on the other hand, have to be considered as normal for human beings (Fig. 78).
As early as 1972 a joint committee of experts from WHO and from the United
Nations Food and Agriculture Organization (F AO) determined the quantity of mercury which may be tolerated in human food: 0.2 mg of methylmercury or 0.3 mg of
total mercury per week for a person, or 0.005 mg total mercury per kg body weight.
This limit is only about ten times lower than the threshold of methylmercury intake
which may result in symptoms of mercury poisoning. But to issue a lower intake
figure than 0.3 mg per person and week would be wishful thinking because mercury
is not only present in contaminated food stuff but occurs in traces everywhere in our
environment, in water, rock, sediment, earth, and in all organisms.
An average citizen in the Federal Republic of Germany has a weekly intake of 0.2 mg
of mercury, that is two thirds the amount health organizations tolerate at all. The
0.2 mg are composed of 0.04 mg from grain, 0.03 mg from alcoholic beverages,
0.02 mg from milk and butter, and among other food stuff, 0.016 mg from the 200 g
(wet weight) fish which the statistical average citizen consumes weekly. The average
mercury concentration in this statistical edible fish is 0.08 mg/kg, mostly present as
methylmercury (Ernahrungsbericht 1976). In the U.S.A., the figures are similar. On
the average, only 14 g fish are eaten per day, about 100 g per week. Concentrated in
this fish, the statistical U.s. citizen takes up 0.014 mg of mercury. This quantity, as
in the Federal Republic of Germany, is only a small fraction of the total mercury
intake with food, which in the U.S.A., too, is not above 0.2 mg per person and week
except for families eating very much fish (Finch 1973).
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8.1 How Much Mercury May Be Tolerated in Fish for Human
Consumption?
Mercury is dangerous for man, as was demonstrated with the casualties of Minamata
(see Chap. 3.2). The United Nations World Health Organization (WHO 1976a) summarized what was known about mercury poisoning and concluded that toxic effects
of mercury can be expected to become manifest in the most sensitive groups of
human adults when over longer periods of time a weekly intake of 1.3-2.9 mg
methylmercury takes place, equivalent 0.02-0.05 mg/kg body weight. Such mercury
intake results in blood concentrations of 0.2-0.5 mg/l and in hair concentrations of
50-125 mg/kg. Victims of the "Minamata Disease" had consumed, with polluted fish,
about 14 mg of mercury per week, and analyses of their blood and hair showed
respectively high mercury concentrations (Table 7). Concentrations of less than
0.02 mg/l in blood and less than 6 mg/kg in hair, on the other hand, have to be considered as normal for human beings (Fig. 78).
As early as 1972 a joint committee of experts from WHO and from the United
Nations Food and Agriculture Organization (F AO) determined the quantity of mercury which may be tolerated in human food: 0.2 mg of methylmercury or 0.3 mg of
total mercury per week for a person, or 0.005 mg total mercury per kg body weight.
This limit is only about ten times lower than the threshold of methylmercury intake
which may result in symptoms of mercury poisoning. But to issue a lower intake
figure than 0.3 mg per person and week would be wishful thinking because mercury
is not only present in contaminated food stuff but occurs in traces everywhere in our
environment, in water, rock, sediment, earth, and in all organisms.
An average citizen in the Federal Republic of Germany has a weekly intake of 0.2 mg
of mercury, that is two thirds the amount health organizations tolerate at all. The
0.2 mg are composed of 0.04 mg from grain, 0.03 mg from alcoholic beverages,
0.02 mg from milk and butter, and among other food stuff, 0.016 mg from the 200 g
(wet weight) fish which the statistical average citizen consumes weekly. The average
mercury concentration in this statistical edible fish is 0.08 mg/kg, mostly present as
methylmercury (Ernahrungsbericht 1976). In the U.S.A., the figures are similar. On
the average, only 14 g fish are eaten per day, about 100 g per week. Concentrated in
this fish, the statistical U.s. citizen takes up 0.014 mg of mercury. This quantity, as
in the Federal Republic of Germany, is only a small fraction of the total mercury
intake with food, which in the U.S.A., too, is not above 0.2 mg per person and week
except for families eating very much fish (Finch 1973).
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