Mercury tolerable weekly intake

The guideline value for mercury is conservative because it is based on the provisional tolerable weekly intake (PTWI) for methylmercury, which is more toxic than mercury. Monitoring would normally only be justified if mercury were known to be present due to unusual circumstances, such as an industrial or mining discharge. 

The tolerable weekly intake (TWI) levels set by World Health Organization for methyl mercury is 1.6 pg/kg body weight. The reference dose (RfD) set by the U.S. EPA is... 

In 2004 the Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives set a provisional tolerable weekly intake of mercury to be 1.6 pg/kg body weight [19]. Also in 2004 the WHO set the following standard for mercury in drinking water 0.001 mg/L [19]. 

In contrast, fish and fish products can be highly burdened with mercury, especially methylmercury. The highest concentrations are found both in marine and freshwater fish at the highest trophic levels of the aquatic food chain, caused by bioaccumulation [4-6] (see Sec. 2.1). The mean mercury concentration in the edible parts of these problem fishes is approximately 1 mg/kg, but peak values even of 10 mg/kg have been reported [16,17]. Shellfish also accumulate methylmercury to a high extent. For instance, the weekly consumption of 200 g of fish containing only 0.5 mg mercury/kg results in the intake of 100 p,g mercury per week [2]. This amounts to one-half of the PTWI (provisional tolerable weekly intake), as recommended by the World Health Organization (WHO) [4,18]. The feeding of animals like chickens with fish meal may raise the mercury burden of terrestrial animal foodstuffs too. 

In contrast, the tolerable weekly intakes of methyl mercury proposed by the WHO amount to 0.2 mg, corresponding to 30 yg daily. However, one should consider recent observations by Bornhausen et al. (1980), and Miisch et al. (1978), who prenatally exposed rats. After a daily exposure of 0.01 mg/kg, that is equivalent to 0.7 mg in adults, between the 6th and 9th days of gestation the animals of the next generation still showed a marked impairment of their learning ability at the age of 4 months. Notably, just as is the case in humans, the mother rats did not show any symptoms. On the basis of this we can assume that prenatally exposed individuals are more sensitive than those subjected to a post natal burden. 

A prolonged intake of cadmium results in its accumulation in the human organism, primarily in fiver and kidney. A level of 0.2-0.3 mg Cd/g kidney cortex causes damage of the tubuli. The tolerable weekly dose for an adult (70 kg) is considered to be 0.49 mg of cadmium. On the whole, the concentrations of the toxic trace elements lead, mercury and cadmium in food show a clearly decreasing tendency, especially in recent studies. This is partly due to inprovements... 

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