Survey of cadmium in food

Fd Cosmet. Toxicol. Vol. 12, pp. 139-142. Pergamon Press 1974. Printed in Great Britain

Review Section REVIEWS

OF RECENT

PUBLICATIONS

Survey of Mercury in Food: A supplementary Report. Working Party on the.Monitoring of Foodstuffs for Heavy Metals: Third Report. Ministry of Agriculture, Fisheries and Food. HMSO, London, 1973. pp. 23. £0.16. Survey of Cadmium in Food. Working Party on the Monitoring of Foodstuffs for Heavy Metals: Fourth Report. Ministry of Agriculture, Fisheries and Food. HMSO, London, 1973. pp. 31.£0.24. When the Working Party named above published its first report in 1971 (Cited in F.C.T. 1972, 10, 399), it recommended that monitoring of food for mercury should continue on a reduced scale, that attention should be paid to possible new sources of mercury contamination, and that the situation should be reviewed after 1 year. As a result, some 2400 additional analyses have now been conducted, and the results are presented in the first of the two reports cited above. It is reassuring that no evidence of any increase in mercury contamination of food has been found. As before, most levels fell below the limit of determination, except in the case of pig kidney and liver, fish and shellfish, and for these commodities results were very similar to those previously obtained. Analyses for methylmercury, carried out on all samples in which total mercury concentrations exceeded 0.1 ppm, revealed that the proportion present as methylmercury ranged from 50-100~ with a mean of about 80~. In the case of canned tuna about 90~ of the 0.2 ppm total mercury content existed in the methyl form, although in fish as a whole the average proportion of methylmercury was lower, at 80~. Some freshwater fish accidentally contaminated with up to 20 ppm mercury from the use of an organomercury dip for seed potatoes contained only a small percentage in the methyl form, and total mercury concentrations dropped rapidly as the distance from the source of contamination increased. Altogether the average diet was estimated to contain only about 0.005 ppm mercury, which in a normal daily intake of 1.5 kg food would lead to a daily consumption of mercury in the range of 5-10 #g, a figure comparing well with the previous estimate of 7-8 #g (ibid 1972, 10, 399). It is also well within the provisional tolerable weekly intake of 0"3 mg total mercury, with a maximum of 0.2 mg methylmercury, proposed by the Joint FAO/ WHO Expert Committee on Food Additives (ibid 1973, 11,655). Appendices to the report contain the recommendations of the Toxicity Sub-Committee (TSC; formerly the Pharmacology Sub-Committee) and of the Food Additives and Contaminants Committee (FACC). The TSC's opinion was that monitoring for mercury could now be confined to total-diet studies carried out periodically during the next 5 years, at the end of which there should be a larger survey covering the same food items. The search for new areas of mercury contamination should continue, with particular reference to discharges into water where fish might be affected, and the attention of everyone working 139

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with mercury compounds should be drawn tO the importance of using correct disposal methods. Results of further monitoring should be submitted to the TSC for scrutiny. The FACC recommended that, in view of the low levels of mercury found in most foods, statutory limits were not necessary at present, but the position should be kept under review. Enforcement authorities and public analysts should take steps to ensure that imports of food containing high mercury levels, particularly those unacceptable in their country of origin, do not find their way on to the UK market. The second report cited above is particularly welcome in view of the current paucity of information on contamination of the British diet with cadmium. Again, the levels in many of the samples were at or below the limit of determination (0.01 ppm), and the vast majority of foods, including fish, contained less than 0.04 ppm. Levels in baby foods were generally below the 0"01 ppm limit. Above-average concentrations were found in certain commodities that are normally of minor importance in the diet, such as kidney (range of means for different types 0.24--0.50 ppm) canned sardines (mean 0-18 ppm), dried herbs (mean 0"79 ppm) and wheat germ (0.10-0-13 ppm), and certain canned vegetables also fell into this category. Fresh potatoes and frozen spinach were also above normal at around 0.08 ppm. However, by far the highest concentrations were found in certain shellfish products, notably in the brown meat of crabs. For this commodity, mean values in the range of ff78-21 ppm were obtained in different coastal areas, with a maximum of 49 ppm in one sample. Shrimps also contained high levels, but more than 80% of the cadmium present was concentrated in the inedible portions. Other edible shellfish presented no general problem, although in the Bristol Channel values were somewhat greater than elsewhere. In this area limpets and dog whelks, neither of which are normally eaten, were particularly highly contaminated, as were winkles, which were fortunately too small and scattered to be consumed in large quantities. Proximity to certain industrial processes or to busy roads increased cadmium levels in leafy vegetables, but preliminary analyses indicated that most of the cadmium was concentrated in the outer leaves. Work is continuing on this aspect and on the effect of sewage sludge, used as a fertilizer, on the cadmium content of crops. On the basis of analyses of total-diet samples, it was calculated that the intake of cadmium in a normal daily diet of 1.5 kg is about 15-30 #g. Water was not analysed for the survey, reliance being placed on a 1961 report from the USA (Schroeder & Balassa, J. chron. Dis. 1961, 14, 236) that the daily intake from this source was not more than 1-2 pg. Since this estimate was later increased by the same team of workers to 15 pg (Schroeder et al. ibid 1967, 20, 179) it seems a little surprising that the UK situation was not investigated more fully. However, on the basis of the lower figure, it is estimated that the weekly UK intake of cadmium does not exceed 250 #g, and such an intake is well within the provisional tolerable weekly intake of 400-500/~g proposed by the Joint FAO/WHO Expert Committee on Food Additives (Cited in F.C.T. 1973, 11,655). The health implications of the ingestion of cadmium in foodstuffs are reviewed by the TSC in an appendix to the report_ It is considered that the kidney is the only organ likely to be affected, and that present ingestion levels should lead to a level of cadmium in the renal cortex well below that regarded as critical. In view of the low consumption of shellfish by most of the population, the high cadmium levels in certain species are not considered to present any general health hazard, but could conceivably constitute a risk for selected individual consumers. It is therefore recommended that epidemiological investigations should be undertaken on such consumers to determine whether their body burden of cadmium is excessive, and to this end appropriate methods applicable to living indivi-

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duals should be developed. These recommendations are endorsed in a further appendix by the FACC, which concludes that there is no need for statutory limits on cadmium in food at present. Monitoring on the present scale should be discontinued, but periodic analyses should be carried out on samples taken for the Total Diet Study, on baby foods and on shellfish. Enforcement authorities should ensure that the situation reflected in the report is not altered adversely, and every effort should continue to be made to reduce environmental contamination with cadmium. As always, the Working Party is to be commended for the thorough nature of its surveys. It is to be hoped that any small omissions, such as the lack of analysis for cadmium in water, will be rectified by the time the next report on this subject is published.

The Environmental and Financial Consequences of Oil Pollution from Ships. Main Report. Intergovernmental Maritime Consultative Organisation: Preparations for International Marine Pollution Conference 1973. Report of Study No. VI submitted by the United Kingdom. Programmes Analysis Unit, Didcot, Berks., 1973. pp. 80. With Appendices 1, 2, 3 and 4, pp. 77, 11,276 and 93, respectively. The object of the study described in this report was to evaluate the damage caused by oil pollution from ships in relation to other sources of oil pollution of the sea, as a basis on which the costs and benefits of preventative methods could be compared. The greater part of the task was carried out by only three people employed for 1 year, so that inevitably the result consists largely of a review of existing data and embodies little new information. Topics surveyed in the main report are the magnitude of oil discharges and their fate at sea, their biological effects and their economic consequences, and the detailed evidence and arguments on these subjects are presented in the separate appendices. The report concludes that the amount of hydrocarbons discharged from human operations is less than that released by natural processes such as the decay of animal and vegetable matter. Although the amount of oil released by tankers is likely to increase markedly by the end of the century, tighter controls will "probably" be brought to bear on non-marine discharges, with the result that the total quantities of oil in the sea might be lowered. No evidence has been discovered of biological damage as a result of low-level (0.05 ppm) chronic pollution, although in extremely localized areas both plants and animals have suffered in the littoral zone from refinery discharges or from large spillages of fuel oil. Bird mortality may involve 50~ or more of the population in certain areas. This is particularly likely in the case of ducks, but such populations are soon restored by rapid breeding. Other species that also tend to congregate in large numbers, such as auks and penguins, are less capable of making good the effects of large-scale destruction, but at present they are found mainly in localities where oil pollution is not a serious threat. The effects on the less common species of diving birds are difficult to assess. Damage to fish and shellfish is dismissed as economically insignificant, despite the fact that some may become so tainted as to be unacceptable. Biodegradation removes harmful oil constituents from the environment at such a rate that little prospect of their accumulation is envisaged; in the case of polycyclic aromatic hydrocarbons, bacterial degradation and metabolism by invertebrates and mammals make it unlikely that such contaminants are passed up the food chain unchanged, and biosynthesis and land run-offare much more important than petroleum as sources of such hydro-