Foodstuffs, mercury levels

Usual flame techniques are often insufficiently detective to measure the low levels of As, Se and Hg present in foodstuffs. Mercury is commonly determined via the flameless cold-vapour technique, whereas there is much current activity in respect of the measurement of As and Se via their conversion to hydrides with subsequent decomposition in cool argon—hydrogen-entrained air flames or electrically-heated cells. Table 4 contains information on these techniques. 

The primary method used to analyse for mercury is CVAAS (cold vapour atomic absorption spectroscopy). This has a sensitivity of parts per trillion for urine while determination of mercury in fish, shellfish, pharmaceuticals and foodstuffs has a sensitivity in the low parts per billion range, as has the analysis of mercury in samples of tissues and hair. Mercury levels in newly formed hair reflect those in blood the concentration however is about 250 times greater in hair. Once the mercury has interacted with the sulphur-containing proteins in hair it is essentially "fixed" and so provides an accurate monitor of exposure and accumulation. Analysis of the hair length can therefore be used to estimate the dates of contamination by mercury and also the peak blood levels achieved. 

Specific recommendations on contaminants (e.g., maximum levels of lead, cadmium or mercury) in foodstuffs are summarized in the European Union Regulations.9 The specifications concerning trace elements in foods and food additives are As < 3mgkg 1, Pb < lOmgkg-1, and Hg and Cd < lmgkg-1. 

EC, Commission Directive 2001/22/EC of 8 March 2001 laying down the sampling methods and the methods of analysis for the official control of the levels of lead, cadmium, mercury and 3-MCPD in foodstuffs, Off. J. Eur. Commun., 1,77 (16 March 2001), 14-21. 

The Commission Regulation No 466/2001 (2001) on maximum levels for certain contaminants in foodstuff contains maximum levels of lead, cadmium and mercury in different kinds of foodstuffs (Table 1.15). This regulation is a legal requirement in all Member States of the European Community since 2002. 

The European Union has implemented Regnlation 466/2001 of the Commission, according to which the maximum permitted tolerance valnes in total mercury in foodstuffs amounts to 0.5 mg/ kg fresh weight product in fishery products, except for certain fishes where the maximum level is 1 mg/kg fresh weight product. 

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. 

Of the metals considered, cadmium and mercury are the most toxic to humans and are also bioaccumulative historically, poisoning incidents by these metals has been via the contaminated foodstuffs pathway. Arsenic is less toxic than cadmium or mercury, as it is more easily eliminated from organisms, but is a more common contaminant and is often present at relatively high levels. In the developing world the most common pathway to humans is via drinking water, but in the UK soil ingestion is of more concern. Chromium is extremely mobile... 

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