Influence of lead migration in tin coatings on trace metal pick-up from tinplate cans

Abstract

A minor source of lead in food cans exists in the form of small impurity levels in the tin of the coating. The level of this impurity in tinplate currently made by the British Steel Corporation is about 0·03 wt-%. It has been shown, using conventional chemical analysis and electron spectroscopy for chemical analysis, that the lead is not uniformly distributed in the coating. A higher concentration of lead has been found near the tin surface, and it has been shown that the lead migrates in the tin at normal ambient temperatures. This explains why some lead pick-up results, previously described as ‘anomalous’, have been higher than would be predicted from the bulk coating tin/lead ratios. The relative severity of attack on this lead by different products is also shown; most foodstuffs, those based on citric acid, will dissolve only a small amount of it. Only foodstuffs based on malic acid and in cans without an internal lacquer will show a significant tendency to attack the lead. The lead pick-up figures in such instances are still very small in relation to legal limits for lead in food.

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