Aluminium and fluoride in hospital daily diets and in teas.

The levels of aluminium and fluoride have been determined in hospital daily diets including breakfast, dinner and supper, as well as in black teas and herbal teas purchased from the local market. In tea, aluminium was determined directly in a sample solution by atomic absorption spectroscopy using nitrous oxide and an acetylene flame. For analysis of the hospital diet, samples containing lower levels of aluminium were analysed using a spectrophotometric method which measured aluminium in the form of a 8-hydroxyquinoline complex. Decomposition of the samples was achieved using a mixture of concentrated acids [nitric (HNO3), perchloric (HClO4) and sulphuric (H2SO4)] in platinum dishes. Fluoride was assayed by spectrophotometry using a microdiffusion procedure with a mixture of concentrated HClO4 and silver sulphate, trace amounts of the released fluoride [as hydrogen fluoride (HF)] were trapped on the alkaline surface of a Petri dish and then determined in the form of an alizarin-fluoride complex. The mean level of aluminium found in hospital daily diets amounted to 21.3 +/- 12.3 mg and the mean level of fluoride was 1.38 +/- 1.12 mg per adult person. In the 16 samples of commerically available brands of black teas, the levels of aluminium and fluoride ranged from 445 to 1552 ppm (mean = 897 +/- 264 ppm) and from 30 to 340 ppm (mean 141 +/- 85 ppm), respectively. In six herbal teas, the mean levels of aluminium and fluoride were lower, and amounted to 218.9 +/- 150.7 ppm and 6.0 +/- 6.9 ppm, respectively. This study has shown that concern about a high intake of aluminium and fluoride from these foods is unfounded.