PETERSON, KLAWE, and SHARP: MERCURY IN TUNAS 



irreversible damage is done before the cause 

 of the symptoms is diagnosed. Other manifesta- 

 tions of methylmercury poisoning are concentric 

 restriction of the visual field or even blindness, 

 inability to coordinate voluntary muscular move- 

 ments, and paralysis. As methylmercury readily 

 crosses the blood-placenta barrier, even an 

 unborn child can be poisoned if its mother is 

 exposed to methylmercury poisoning. Very little 

 is known about the subclinical effects of methyl- 

 mercury. 



It is interesting to note that Ganther et al. 

 (1972) found that the increase in mercury con- 

 tent between two lots of canned tuna examined, 

 one of low mercury content (0.32 ppm average) 

 and the other of high mercury content (2.87 

 ppm), was in an approximate 1:1 molar ratio 

 with the increase in selenium. Furthermore they 

 found that selenium added to the diet of rats 

 in quantities comparable to that found in tuna, 

 decreased methylmercury toxicity in the rats. 

 These authors suggest that selenium in tuna 

 may actually lessen the danger to man of 

 mercury in tuna. 



MERCURY STANDARDS FOR 

 FISH AND FISH PRODUCTS 



Currently, only about 13 countries have 

 established standards for the allowable amount 

 of mercury in fish and fishery products for 

 human consumption. These standards, ranging 

 from 0.5 to 1.0 ppm, are expressed in parts 

 per million by wet weight and refer to total 

 metallic mercury (the organic and inorganic 

 compounds of mercury are reduced to metallic 

 mercury during the analysis). 



The acceptable limits of mercury in fishes 

 and other aquatic organisms are based on 

 investigations (Berglund et al., 1971) of clini- 

 cally detectable poisoning of adults sensitive to 

 methylmercury which indicate that manifesta- 

 tions appear at a blood level of 0.2 ji gig (ex- 

 pressed as metallic mercury per gram of whole 

 blood). This level is attained by exposure to 0.3 

 mg of mercury (as methylmercury) per day 

 taking into account the fact that the human 

 body excretes methylmercury at a rate which 

 eliminates half of the amount present in 70-90 

 days (Aberg et al., 1969; Berglund et al., 1971). 



A prestigious Expert Panel appointed by the 

 Swedish Board of the National Institute of 

 Health, in consultation with the Swedish Na- 

 tional Board of Health and Welfare and the 

 Swedish National Veterinary Board, applied 

 a safety factor of 10 to arrive at 0.02 /ig/g as 

 an acceptable level of mercury (as methyl- 

 mercury) in whole human blood and 0.03 mg 

 as an acceptable daily intake of methylmercury 

 (Lambou, 1972). 



It is generally accepted by researchers and 

 health authorities that with the exception of 

 contaminated wildlife, grain, etc., food of ter- 

 restrial origin is relatively free of mercury in 

 general and of methylmercury specifically, and 

 that the only significant source of methyl- 

 mercury in the human diet is fish and other 

 aquatic organisms (Nelson et al., 1971). In 

 calculations of dietary intake of methylmercury 

 and in the formulation of mercury standards, 

 generally only this class of food is taken into 

 consideration. Therefore, to evaluate the risk 

 of mercury to the general population it is 

 necessary to know the daily or weekly con- 

 sumption of fish and other aquatic animals. 



The Swedish Commission on Evaluating the 

 Toxicity of Mercury in Fish recommended an 

 allowable weekly intake of mercury equivalent 

 to 210 g of fish containing 1.0 ppm of mercury. 

 However, some experts are cautioning that a 

 level of 1.0 ppm in fish might result in a high 

 mercury intake in some individuals eating more 

 fish than the average for the Swedish popula- 

 tion, thus attaining the lowest levels shown 

 clinically to be present in persons sensitive to 

 methylmercury poisoning. 



The Swedish findings on mercury contamina- 

 tion of fish from some lakes and rivers caused 

 the Food and Drug Administration (FDA) of 

 the U.S. Government to begin its own evalua- 

 tion, and an "in-house" standard of 0.5 ppm 

 was adopted in May of 1969. If all fish and 

 shellfish contained 0.5 ppm mercury, the daily 

 limit of 0.03 mg of mercury could be reached 

 by eating 420 g of fish and shellfish per week. 

 A. C. Kolbye of FDA, during a hearing before 

 a Congressional Subcommittee, stated that the 

 average weekly intake of fish in the United 

 States is 280 g. However, a survey of the U.S. 

 Department of Agriculture states that the 



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