Inorganic contaminants in food

The presence of elements known to have adverse health effects in humans such as lead and arsenic is obviously undesirable in food. Environmental sources are the main contributors to contamination of food with most metals and other elements. Some elements (e.g. arsenic) are present naturally but the major sources of other elements (e.g. lead) in the environment are from pollution from industrial and other human activities. The presence of metals and other elements in food can also be the result of contamination from certain agricultural practices (e.g. cadmium from phosphate fertilisers) or manufacturing processes (e.g. tin in canned foods). 

Statutory legislation to control the levels of such substances in food has been introduced in the UK and elsewhere. In more recent years, other potentially toxic elements have come into focus. Lead, cadmium and mercury have been the subject of much monitoring of the food chain and other metals, in particular aluminium, are continuing to attract attention. Nitrate and nitrite in food from food additive use is regulated across the European Union, but its presence in food crops has raised concerns. 

A comprehensive programme of work for the surveillance of the food supply has been established for a long time in the United Kingdom to ensure that contamination of the food supply by inorganic contaminants is kept to a minimum.1 The surveys under this programme have provided a considerable amount of data that are of value for use in estimating the dietary exposure to the various contaminants. 

In order to estimate dietary exposure, data on concentrations of heavy metals are combined with data on consumption of foodstuffs. Among the methods 

The UK Total Diet Study (TDS) relies on nationally representative information about the average food consumption by individual households researched in the UK National Food Survey (based on a survey of approximately 7000 households).2,3 Typical diets are constructed based on these data. Foodstuffs are purchased from retail outlets, then prepared and cooked in the normal manner. The individual foodstuffs are then usually combined into various groups of similar foods - for example cereals, green vegetables and fish - in the proportions eaten on average by consumers. Population dietary exposures can then be calculated using data from the TDS samples. 

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The efficient recovery of volatile nitrosamines from frankfurters, followed by gc with chemiluminescence detection, has been described (133). Recoveries ranged from 84.3 to 104.8% for samples spiked at the 20 ppb level. Methods for herbicide residues and other contaminants that may also relate to food have been discussed. Inorganic elements in food can be deterrnined by atomic absorption (AA) methods. These methods have been extensively reviewed. Table 8 Hsts methods for the analysis of elements in foods (134). 

Cells R, Cox L, Hermosin MC, Cornejo J (1996) Retention of metamitron by model and natural particulate matter. Intern J Environ Anal Chem 65 245-260 Chaney RL (1989) Toxic element accumulation in soils and crops protecting soil fertility and agricultural food chains. In Bar Yosef B, Barrow NJ, Goldschmid J (eds) Inorganic contaminants in the vadose zone Springer, Heidelberg, pp 140-159 Charlatchka R, Cambier P (2000) Influence of reducing conditions on solubility of trace metals in contaminated soils. Water, Air Soil PoUut 118 143-167 Chien SH, Clyton WR (1980) Application of Elovich equation to the kinetics of phosphate release and sorption in soils. Soil Sci Am J 44 265-268... 

Brines maybe, as the name suggests, solutions of inorganic salts in water, and the two in general use are sodium chloride and calcium chloride. Of these, the former is compatible with most foodstuffs and can be used in direct contact or in circumstances where the brine may come into contact with the product. Calcium chloride has an unpleasant taste and cannot be permitted to contaminate foods. 

These are estimates of dietary exposure to inorganic contaminants for individuals who eat average amounts of food (i.e. mean consumers) and those who eat more than average (i.e. upper range (97.5th percentile) consumers) and are based on consumption data from the UK National Adult Dietary Survey (NADS).4 They are calculated using the mean upper bound concentrations of specific contaminants in each food group and the consumption data from the NADS. Consumer exposure estimates are less suitable for following trends in exposure than population estimates as they are based on consumption data from the NADS which was carried out only once in 1986 and 1987 and is not updated... 

Like many other inorganic contaminants, lead is ubiquitous and can be found naturally occurring in many different foods as metallic lead, inorganic ions and salts. Lead has no essential function in man, but has a number of adverse effects and young children and the developing foetus are considered to be at most risk from its toxic effects.5... 

Chemical contamination does not respect international borders. The contaminants are spread worldwide by air and water. Environmental organic contaminants and inorganic contaminants such as metals and metal compounds, nitrate and nitrite will be present in all foods, though sometimes in quantities below the limit of detection of the analytical methods of today. Moreover, foods as well as raw materials and ingredients for food production are to an increasing extent traded across borders. 

A. A. Abdelghani, Y. V. Pramar, T. K. Mandal, P. B. Tchouwou, L. Heyer, Levels and toxicides of selected inorganic and organic contaminants in a swamp environment, J. Environ. Sci. Health, Part B Pesticides, Food Contam. Agric. Wastes, B30 (1995), 717-731. ... 

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