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Science Alert: Experts Respond

Melamine leaching from plastic tableware – experts respond

Posted in Science Alert: Experts Respond on January 22nd, 2013.

Tableware made from melamine-containing plastics may leach some of the compound into food if it is served hot, according to new research. However independent experts are unsure of what health impact – if any – such small doses could have.

In a new study published in JAMA Internal Medicine, Taiwanese researchers measured the  the melamine levels in the urine of people who had eaten hot noodles from either melamine or ceramic bowls. Their results showed consumption out of melamine bowls led to higher levels of melamine excreted in urine than those who ate out of the ceramic bowls.

The health risks of the compound melamine, used as a resin in plastics, were highlighted by the 2008 tainted infant formula scandal. The compound has been linked to kidney damage at high doses.

The authors caution that melamine tableware “may release large amounts of melamine when used to serve high-temperature foods”, but don’t postulate what effect this can have on the body. They also note that the amount of melamine released into food and beverages from melamine tableware varies by brand, so the results of this study of one brand may not be generalized to other brands.

An invited comment article by Toxicologist Pertti J. Hakkinen, published alongside the study, gives an overview of how readers should interpret studies highlighting potential health risks.

Our colleagues at the AusSMC collected the following expert commentary. Feel free to use these quotes in your reporting. If you would like to contact a New Zealand expert, please contact the SMC (04 499 5476; smc@sciencemediacentre.co.nz).

Dr Ian Musgrave, Senior Lecturer in the Faculty of Medicine, University of Adelaide, comments:

“Melamine is familiar to us as the base chemical which makes the robust melamine plastic tableware. Melamine is also infamous as an illegal adulterant in pet food and children’s milk formulas. The milk contamination resulted in the deaths of six children and kidney problems in many more. The levels of melamine that caused these problems was enormously higher than that we are likely to consume from our normal diet. However, long term consumption of lower levels of melamine may be associated with an increased risk of kidney stones.

“The paper by Wu et al provides a possible route of melamine exposure. Very hot foods in melamine plastic tableware can cause melamine to leach into the food. Wu et al show that hot (90 degree) soup will leach melamine from melamine plastic soup bowls and this is absorbed by the body and excreted in the urine. They showed that the melamine is very rapidly excreted, and that the total levels excreted suggest an exposure to melamine over 600 times lower than the most stringent exposure limit. This is despite the researchers using a brand of melamine ware with the highest melamine leaching on contact with hot fluids.

“What we don’t know is whether the contact time with the soup was representative of standard household or restaurant use (how many families will serve soup at 90 degrees C, not that far from boiling). If anything, it is likely the risk form standard household use is even less than this study indicates.

“The Wu et al study suggests that even with a melamine ware that has a very high level of melamine leaching, the level of melamine exposure that results may have very minor health impacts, if any at all. However, the fact that even small amounts of melamine can leach from these ubiquitous food containers at high temperatures should make us cautious. It may be useful to test melamine tableware for melamine leaching, and only permit the sale of low leachant tableware. It may also be prudent to avoid keeping very hot foods in melamine bowls for extended periods of time”.

Comments collected by UK Science Media Centre:

Prof Sir Colin Berry, Emeritus Professor of Pathology, Queen Mary University of London, said:

“This study has a good experimental design and shows very small amounts of melamine excreted, as expected. As the authors point out, no comments can be made about effects but at low levels of melamine you would not expect toxicity. The ‘follow-up’ paper would be to see if those who used melamine always have more stones than those who don’t. But you would need huge numbers to carry this out so I am not sure it could be done. The findings of the current study are, in my view, noise of no clinical significance.”

Professor Alan Boobis, Professor of Biochemical Pharmacology at Imperial College London, said, said:

“Melamine is a well studied compound.  Its primary toxic effect is to the kidney. The effect is highly dependent on the dose, as it is a consequence of crystallisation of melamine. At doses below those which produce sufficient amounts in the urine to crystallise there is no adverse effect.  Hence, exposure to small amounts of melamine will not cause any harm. According to EFSA and the WHO, regular exposure to melamine in amounts of up to 0.2 mg per kg body weight in the diet on a daily basis (the tolerable daily intake) would not be expected to cause any harm.  Indeed, it has been known for some time that consumers can be exposed to small amounts of melamine through the use of melamine cookware and this does not result in exceedence of the tolerable daily intake.

“EFSA evaluated a number of use scenarios of melamine cookware and concluded that none resulted in levels that would exceed the tolerable daily intake. This is confirmed in the study by Wu et al.  Total excretion of melamine (almost all of which when ingested will be excreted in the urine) was maximally around 0.02 mg.  Given that the tolerable daily intake is 0.2 mg/kg bw, equivalent to 14 mg per 70 kg adult or 2.4 mg per 12 kg toddler (1-3 years of age), one would have to consume very many portions (>200 by a toddler) of food cooked as in the Wu et all study in a single day before the tolerable daily intake was exceeded.”
Professor Tony Dayan, Emeritus Professor of Toxicology, University of London, said:

“Melamine is a monomer that is polymerised in the manufacture of resins used to make bowls and other containers for domestic use. Similar resins occur in other food containers and in adhesives used to seal and label various food packs. It may also occur in foodstuffs as a metabolite of a pesticide. Its biological and toxicological properties have been extensively studied, even before the contaminated milk and animal food scandal a few years ago.

“Major regulatory agencies, such as WHO [see WHO below], the US FDA (see FDA below) and the European EFSA [see EFSA below] have published formal reviews of its toxicity from which various estimates have been derived of the ‘Tolerable Daily Intake’ (TDI) in man considered not to represent any risk to consumers. The estimates have ranged from 0.63 to 0.2mg/kg/d for adults. The potential toxicity of the association in foodstuffs of melamine and the related substance cyanuric acid is included in these estimates. The principal risk, as shown in the recent contaminated milk scandal is the formation of kidney and bladder stones if sufficient melamine is ingested regularly for months on end.

“The new report from Taiwan continues work started there some time ago showing that melamine may be leached from containers holding hot, acid liquids, such as certain types of soup (Chien et al, 2011).

“The new report suggests that the intake of melamine from 500mL hot soup in melamine resin bowls may result in the urinary excretion of melamine up to 8.35?g/day. When the subjects ate the soup from ceramic bowls they excreted melamine 1.31?g/day.  Urinary excretion of melamine is a reasonable indicator of the total amount ingested by the person.

“The new research was done because of concern about the high incidence of such stones in Taiwan and their possible relationship to melamine in the diet (Liu et al, 2012; Lopez et al 2012).

“ Conclusion: Much has still to be done to quantify the frequency and the concentration of melamine monomer in the diet in every country and its relationship to the quantity excreted in the urine but the amounts now demonstrated seem small in relation to what is generally accepted as a tolerable daily dose. The new information does not suggest a major new risk factor in the causation of kidney and bladder stones particularly when the very varied nature of the foodstuffs likely to be stored and served in melamine resin bowls are considered many of which will probably not leach any of the monomer from the resin or adhesive.”

References from Tony Dayan

·         Chien C-Y et al 2011. High melamine migration in daily-use melamine-made tableware. J Hazardous materials, 188 (1-3), 350–356
·         EFSA 2010. Scientific Opinion on Melamine in Food and Feeding Stuffs. At http://www.efsa.europa.eu/en/efsajournal/pub/1573.htm

·         FDA Update: Interim Safety and Risk Assessment of Melamine and its Analogues in Food for Humans November 28, 2008

·         And Peer Review Report July 2009

·         For both see http://www.fda.gov/Food/FoodSafety/FoodContaminantsAdulteration/ChemicalContaminants/Melamine/default.htm
·         Hau AK et al 2009. Melamine Toxicity and the Kidney. Am J Soc Nephrol, 20, 245-290
·         Liu CC et al 2012. Reappraisal of melamine exposure and adult calcium urolithiasis. Kidney Internat, 82, 361-362

·         Lopez FJ, Quereda C. Melamine toxicity: one more culprit in calcium kidney lithiasis. Kidney Int 2011; 80: 694–695

·         WHO  Melamine and Cyanuric acid: Toxicity, Preliminary Risk Assessment and Guidance on Levels in Food 25 September 2008 – Updated 30 October 2008.

·         At http://www.who.int/foodsafety/fs_management/Melamine.pdf

 

 

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