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What You May Not Know About Melamine Toxicity

On October 25, 2008, Hong Kong officials announced the discovery of melamine (CAS Registry Number 108-78-1) contamination in eggs imported from China.¹  This news came soon after the announcement that melamine was found to contaminate Chinese baby formula and speculation that it played a role in causing kidney-related illness in thousands of infants.² 

What exactly is melamine?  According to the U.S. Food and Drug Administration (FDA), this synthetic compound is:

...a small, nitrogen-containing molecule that has a number of industrial uses, including as a binding agent, flame retardant, and as part of a polymer in the manufacture of cooking utensils and plates, plastic resins, and components of paper, paperboard, and industrial coatings.³

You probably wouldn't sprinkle melamine on your French fries, but did you know that melamine has a safety profile comparable to common table salt (sodium chloride; CAS Registry Number 7647-14-5)?  Toxicity information in CAS databases indicates that the amount of table salt required to kill half of a sample population (LD₅₀ in rats) is actually less than it is for melamine:

• Sodium chloride = 3800 mg/kg
• Melamine = 6000 mg/kg

If melamine is relatively nontoxic, how is it linked to kidney-related illness?  The answer may be tied to the melamine analog, cyanuric acid (CAS Registry Number 108-80-5).  In the spring of 2007, the FDA named melamine as the principal contaminant in pet food that appeared to be causing kidney failure in cats and dogs.³  A recent article abstracted in CAS databases suggests that the kidney toxicity observed in these animals was likely due to the consumption of food contaminated with both melamine and cyanuric acid.⁴  These two substances interact by hydrogen bonding to form a crystalline melamine-cyanuric acid complex (CAS Registry Number 37640-57-6).  When co-ingested, melamine and cyanuric acid form "an insoluble precipitate in kidney tubules that is of sufficient severity to cause renal failure via physical blockage."

While these findings may explain the 2007 kidney failures in cats and dogs, it's too early to tell if they have any relevance to the recent reports of kidney-related illness in Chinese infants.  You can learn more about the latest research on melamine, cyanuric acid, and the melamine-cyanuric acid complex in the CAS databases.

For additional information about food safety, see the ACS Global Challenges/Chemistry Solutions podcast, Providing Safe Food.

Contributed by
Peter S. Carlton, Ph.D.
CAS Communications

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References

1. Barboza, D. Tainted Eggs From China Discovered in Hong Kong. The New York Times, Oct 27, 2008, p A6.
2. Chao, L. Tainted Baby Formula Blamed In Chinese Kidney Cases. The Wall Street Journal, Sept 12, 2008, p A10.
3. U.S. Food and Drug Administration. http://www.fda.gov (accessed Nov 5, 2008).
4. Dobson, R.L.M.; Motlagh, S.; Quijano, M.; Cambron, R.T.; Baker, T.R.; Pullen, A.M.; Regg, B.T.; Bigalow-Kern, A.S.; Vennard, T.; Fix, A.; Reimschuessel, R.; Overmann, G.; Shan, Y.; Daston, G.P. Identification and Characterization of Toxicity of Contaminants in Pet Food Leading to an Outbreak of Renal Toxicity in Cats and Dogs. Toxicol. Sci. 2008, 106(1), 251-262. 

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