Brazilian lead: Pewterware reveals illegal heavy metal

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  • Published: Jun 15, 2011
  • Author: David Bradley
  • Channels: Atomic
thumbnail image: Brazilian lead: Pewterware reveals illegal heavy metal

Taking the lead

It is illegal to use lead as an additive in the manufacture of pewter kitchenware, tableware, drinking cups. However, work in Brazil using atomic absorption spectroscopy not only provides a benchmark for standardizing tests for lead, cadmium and other toxic metals, but reveals that some manufacturers are flouting the law.

Tin is a useful metal, but is relatively soft, the addition of hardening agents at a low concentration, such as antimony, bismuth, copper or lead were found to make tin products more durable in the form of pewter. The composition of pewter for domestic use is now tightly controlled, based on British and European standards, and pewter products must today contain a minimum of 90% tin with antimony and copper making up the remaining 10%, sometimes with bismuth taking a small proportion of that. The well-known toxicity of lead means it is no longer permitted, although antique pewter dating from the seventeenth and eighteenth centuries will, of course, contain a proportion of the heavy metal.

Maria Goreti Vale of the Universidade Federal do Rio Grande do Sul in Porto Alegre and the Universidade Federal de Bahia in Salvador, and colleagues there and at the Universidade Federal de Santa Catarina, Florianópolis and the Universidade Federal de São João del-Rei, Brazil, have developed two simple methods for the determination of cadmium and lead in different kinds of beverages and vinegar leached from pewter cups produced in Brazil based on graphite furnace atomic absorption spectrometry.

Leaching tests

The team carried out leaching experiments with different mixtures of beer, sugar cane spirit, red and white wine, vinegar and a 3% acetic acid solution in various vessels including cups made with and without solder. The mixtures were left to stand in the vessels for 24 hours and AAS applied for lead and cadmium analysis with deuterium background correction. The team report a limit of detection of 0.05 and 1.4 micrograms per litre with the characteristic mass of cadmium being 1.0 picograms and 19 picograms of lead. "With the developed methods it was possible to determine accurately cadmium and lead by direct analysis in these liquids and to evaluate the leaching of these metals from pewter cups," the team says, "The results show that pewter cups are not cadmium- and lead-free; this point goes against the manufacturers' declaration that their products are lead-free."

The team points out that pewter was very fashionable until the 19th century being employed in utensils and objects for eating, drinking, celebrating, lighting and taking communion. It then fell out of fashion for a time but is enjoying something of a Renaissance worldwide, consumers and artisans having rediscovered the beauty and functionality of fine pewter. Indeed, pewter production is an important source of income for São João del-Rei in Brazil, which is one of the major centres for pewter artefacts in Latin America. As such, ensuring that consumers are not being exposed to toxic elements, such as cadmium and lead is rapidly becoming an important aspect of regulatory control in the pewter market. The simple AAS technique developed by Vale and colleagues could be used in ensuring product safety.

"We do not have any proof that lead and/or cadmium have been added intentionally, or if these elements have been introduced accidentally with the raw materials," Vale told SpectroscopyNOW. "The recommendation that should be given is that the manufacturers should control their raw materials and their final products using reliable analytical methods, such as the ones developed in the present work in order to make sure that their products meet international regulations."

 

     

Gabriel Metsu - The Old Drinker [c.1658] with pewter tankard

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