1 mg/kg 7 is the maximum mercury concentration allowed in edible fish in Sweden,
Japan, Switzerland, and, according to the Regulation on Maximum Amounts of Mercury in Fish, Crustacea and Molluscs from 1975, in the Federal Republic of Germany.
In Italy the rule is 0.7 mg/kg, in the USA and Canada 0.5 mg/kg, but in Norway
1.5 mg/kg. The variety of limits is a mirror of the difficulties which governments
encounter in setting reasonable standards.
Governments want to be sure that mercury from industrial and other marine pollution does not find its way to the dinner of the citizen. In fact the regulations of all
countries mentioned, from 0.5 to 1.5 mg/kg, safeguard against a drastic pollution
catastrophe like Minamata, if properly monitored. The question, however, remains to
be discussed what level of mercury concentration can be achieved and can be tolerated
in such fish which live in nearshore and estuarine regions polluted by rivers and other
diffuse sources, and what to do with high natural mercury concentrations in some
fish. The question becomes more complex, too, by the fact that one has to consider
the risks of people who eat considerable quantities of fish.
In the U.S.A. the statistical average citizen eats 14 g of fish per day, but 1 % of the
population eat 77 g/day, and 0.1% of the population eat as much as 165 g/day, or
1155 g of fish per week (Finch 1973). Eating fish with 1 mg/kg mercury, such a
person would take in 1.3 mg mercury per week, 1.1 mg from fish and 0.2 mg from
other food. This exceeds about four times the quantity tolerated for the average
person; when fish with 0.5 mg/kg of mercury is eaten, the mercury quantity taken
up is double the tolerance set for an average citizen. 0.5 mg/kg of mercury quite
regularly occur in fish from such estuaries and coastal seas which are generally polluted, like the Irish Sea, the mouth of Thames and Rhine, of Weser and Elbe (see
Chap. 3.2 and 4.2). In negotiations about the Paris Convention (see Chap. 10) regarding marine pollution from land, efforts are under consideration to fight mercury pollution with the aim that marine fish should not have more than 0.3 mg/kg of mercury in their meat. But at present this goal has not been achieved. If one sets the tolerance limit for mercury in fish at 0.3 mg/kg, some fish could not be sold any longer,
if one sets the limit at 1 mg/kg, there might be a risk for extraordinary fish eaters.
It is good to know that all the species of edible sea fish which are landed in great
quantities in the German fishery ports have only small concentrations of mercury in
their meat (Meyer 1972; Priebe 1976). Concentrations in cod (Gadus morhua), coalfish (Pollachius virens), haddock (Melanogrammus aeglefinus), herring (Qupea harengus), and mackerel (Scomber scrombrus) are generally 0.05-0.1 mg/kg, very rarely up
to 0.4 mg/kg, and only very exceptionally, in very old larger fishes, up to 1 mg/kg.
This fish reach catchable size in 5-8 years. Flatfish (Pleuronectidae) have somewhat
higher concentrations of 0.1-0.2 mg/kg, perhaps because they come into contact
with the sediment of the sea bottom.
Again somewhat higher, up to 0.25 mg/kg are mercury concentrations in catfish
(Anarhichas) and redfish (Sebastes), both of which grow slowly. A wide-ranging analysis of North Sea fish has shown that mercury concentrations are, in general, not
higher than in fish from the open Atlantic: cod 0.13 mg/kg (variation 0.03-0.26),
7 If not stated otherwise, all data on concentrations of mercury in organic tissues, given in this
chapter, are per wet weight
148
Japan, Switzerland, and, according to the Regulation on Maximum Amounts of Mercury in Fish, Crustacea and Molluscs from 1975, in the Federal Republic of Germany.
In Italy the rule is 0.7 mg/kg, in the USA and Canada 0.5 mg/kg, but in Norway
1.5 mg/kg. The variety of limits is a mirror of the difficulties which governments
encounter in setting reasonable standards.
Governments want to be sure that mercury from industrial and other marine pollution does not find its way to the dinner of the citizen. In fact the regulations of all
countries mentioned, from 0.5 to 1.5 mg/kg, safeguard against a drastic pollution
catastrophe like Minamata, if properly monitored. The question, however, remains to
be discussed what level of mercury concentration can be achieved and can be tolerated
in such fish which live in nearshore and estuarine regions polluted by rivers and other
diffuse sources, and what to do with high natural mercury concentrations in some
fish. The question becomes more complex, too, by the fact that one has to consider
the risks of people who eat considerable quantities of fish.
In the U.S.A. the statistical average citizen eats 14 g of fish per day, but 1 % of the
population eat 77 g/day, and 0.1% of the population eat as much as 165 g/day, or
1155 g of fish per week (Finch 1973). Eating fish with 1 mg/kg mercury, such a
person would take in 1.3 mg mercury per week, 1.1 mg from fish and 0.2 mg from
other food. This exceeds about four times the quantity tolerated for the average
person; when fish with 0.5 mg/kg of mercury is eaten, the mercury quantity taken
up is double the tolerance set for an average citizen. 0.5 mg/kg of mercury quite
regularly occur in fish from such estuaries and coastal seas which are generally polluted, like the Irish Sea, the mouth of Thames and Rhine, of Weser and Elbe (see
Chap. 3.2 and 4.2). In negotiations about the Paris Convention (see Chap. 10) regarding marine pollution from land, efforts are under consideration to fight mercury pollution with the aim that marine fish should not have more than 0.3 mg/kg of mercury in their meat. But at present this goal has not been achieved. If one sets the tolerance limit for mercury in fish at 0.3 mg/kg, some fish could not be sold any longer,
if one sets the limit at 1 mg/kg, there might be a risk for extraordinary fish eaters.
It is good to know that all the species of edible sea fish which are landed in great
quantities in the German fishery ports have only small concentrations of mercury in
their meat (Meyer 1972; Priebe 1976). Concentrations in cod (Gadus morhua), coalfish (Pollachius virens), haddock (Melanogrammus aeglefinus), herring (Qupea harengus), and mackerel (Scomber scrombrus) are generally 0.05-0.1 mg/kg, very rarely up
to 0.4 mg/kg, and only very exceptionally, in very old larger fishes, up to 1 mg/kg.
This fish reach catchable size in 5-8 years. Flatfish (Pleuronectidae) have somewhat
higher concentrations of 0.1-0.2 mg/kg, perhaps because they come into contact
with the sediment of the sea bottom.
Again somewhat higher, up to 0.25 mg/kg are mercury concentrations in catfish
(Anarhichas) and redfish (Sebastes), both of which grow slowly. A wide-ranging analysis of North Sea fish has shown that mercury concentrations are, in general, not
higher than in fish from the open Atlantic: cod 0.13 mg/kg (variation 0.03-0.26),
7 If not stated otherwise, all data on concentrations of mercury in organic tissues, given in this
chapter, are per wet weight
148