Arsenic compounds in food

For reasons of safeguarding human health, government bodies set guidelines for acceptable maximum concentrations of chemicals in foods. For arsenic, the concentration is generally set at 1 mg/kg (wet mass), and is based on arsenic being present as the inorganic compound arsenous acid. Arsenous acid is a toxic form of arsenic; it is a common trace constituent of our environment and consequently is found in water and foods, generally at low levels. Arsenic can also form organoarsenic compounds, and these compounds also occur in our environment and in foods. Indeed, the organoarsenicals are the major arsenic forms in biological material, and as a result, many foods contain arsenic at high concentrations - well in excess of the maximum acceptable level. Despite their high arsenic content, such foods are considered safe for consumers because the organoarsenic compounds that they contain have no known toxicity. Modern analytical methods are able to determine the various chemical forms of arsenic present in, for example, food items. These techniques, however, can only be applied to aqueous extracts of samples, and consequently, they only provide information about the water-soluble arsenic compounds in foods. A large part (up to 50%) of the arsenic in foods is not water-soluble, and has so far escaped analysis and identification. The chemical and toxicological properties of these unidentified forms of arsenic remain unknown. The proposed project will address this issue by investigating the water-insoluble arsenic constituents in organisms with a focus on those contributing to the human diet. The approach will be to identify those organisms with high concentations of water-insoluble arsenic, and use one or more of such type of organisms as a source of the arsenic compounds. Some of this arsenic will consist of lipid- soluble compounds, and these will be purified and identified by spectrosopic means. The presence, significance and properties of other water-insoluble compounds will also be determined. After these previously unreported forms of arsenic have been characterised, their presence and concentrations will be determined in a range of common foodstuffs. The project will produce the first complete analysis of all arsenic forms present in foods. These data will form a sound basis for scientific assessment of the significance to human health of arsenic in foods.

Arsenic, present in drinking water as inorganic arsenic forms, is a known human carcinogen, and there are regulations controlling the maximum arsenic concentration permitted in drinking water supplies. Some foods also contain large amounts of arsenic, in a variety of forms, but there are currently no regulations in Europe controlling this source of arsenic. The project had the overall goal of providing information on the forms of arsenic found in foodstuffs to enable scientists in the areas of food, health and safety to assess possible detrimental effects of arsenic in food and frame appropriate regulations. Three significant advances were made. First, a method was developed for the measurement of lipid-soluble arsenicals (arsenolipids) which are present in fatty foods, in particular fish oils. The technique enables the separation of the major arsenolipids, and their quantification in terms of their arsenic concentration, although their identity remains unknown. The methods were applied to investigate the arsenolipids in fish oil supplements which are commonly taken as a rich source of omega-3 fatty acids. Further, human metabolic studies were undertaken with arsenolipids naturally contained in cod liver and cod liver oil. These studies demonstrated that the arsenolipids were readily taken-up from the gut and were bioavailable to humans; they were biotransformed to dimethylarsinate and several novel human arsenic metabolites which together accounted to >90% of the ingested arsenic. The major metabolite from arsenolipids, dimethylarsinate, is also the major metabolite after ingestion of inorganic arsenic present in drinking water. These data provide a strong case for consideration of food-arsenic when assessing the risk factors associated with humans exposed to arsenic. Second, a new type of arsenic compounds, thio-arsenicals, were identified for the first time as natural constituents of canned mussels, and subsequently shown by our group and other research groups to be present in a range of seafood products. Specific analytical methods for the determination of thio-arsenicals were developed and are now widely used by researchers in this field. Several of these compounds were synthesised in the laboratory ahead of toxicity testing with human cell cultures. Third, a method involving derivatisation of arsenicals (commonly termed "hydride generation") was developed for investigating arsenic species in biological extracts. The work showed that accepted dogma concerning the selectivity of the "hydride generation" methods was wrong and could lead to a vast over- estimation of toxic arsenic species.