The FDA’s Center for Veterinary Medicine announced in separate releases during the week beginning April 22, 2007 that a second contaminant, cyanuric acid, was found in recalled pet food and pet feed distributed in the United States, and that batches of rice protein concentrate also used in pet food were laced with melamine, the same additive linked to at least 16 confimed pet deaths. Cyanuric acid, a by-product of melamine that has a toxic effect on human kidneys in high doses, was found in urine and tissue samples taken from animals fed with products containing melamine.

The director of the FDA’s Center for Veterinary Medicine said melamine may have been deliberately added to wheat gluten and rice gluten to artificially inflate the protein levels in the products, which might garner a higher price on the U.S. market. Wheat and rice gluten are forms of protein used as binders in soft, or wet, pet food to enhance the protein content.

Researchers in three different North American labs found cyanuric acid, amilorine and amiloride, all by-products of melamine, in spoke-like crystals found in samples of animal urine, tissue and kidneys taken from animals on farms that were fed food contaminated with melamine. Cyanuric acid can result from the bacterial degradiation of melamine, according to Richard Goldstein, a kidney specialist at the Cornell University School of Veterinary Medicine and one of the researchers.

Cyanuric acid is typically used in chlorination during pool cleaning and is not known to be highly toxic in small doses. “People swallow it all the time,” Dr. Goldstein said. However, “it does have a toxic effect on the kidneys in very high doses… . Combining it with melamine may cause it to crystallize and hang out in the kidneys a lot longer than normal.”

The international chemical safety card for cyanuric acid listed on the website for the Centers for Disease Control and Prevention (CDC) indicates that ingestion of cyanuric acid in large amounts could result in tissue lesions on the kidneys. Tests on cyaunuric acid on dogs and rats have found it safe. Researchers also found amilorine and amiloride, other by-products of melamine, in the samples, but pointed to cyanuric acid as the most significant of the three by-products because of its link to tissue lesions. Tissue lesions in the kidneys may have to be repaired with surgery and can lead to kidney failure.

Health officials are now trying to determine whether humans may have consumed food containing melamine and if a danger exists in the U.S. food supply. The FDA named six grain products frequently imported into the U.S. that could potentially be contaminated from melamine additives:

• Wheat gluten,
• Corn gluten,
• Corn meal,
• Soy protein,
• Rice brain, and
• Rice protein.

The six grain additives could be used in thousands of food products ranging from baby formulas and baby food to cereals and breads. The agency is working with the U.S. Department of Agriculture (USDA) to investigate at least 10 hog farms in six states (North Carolina, South Carolina, California, New York, Utah and possibly Ohio) that were quarantined after it was discovered that the farms’ animals were fed with feed tainted with melamine shipped by a supplier that imported it from China.

Senators Dick Durbin (D-IL) and Marie Cantwell (D-WA) sent a letter to FDA Commission Andrew von Eschenbach on April 23rd demanding the agency release the names of companies that received contaminated supplies from China, and identify and inspect all suspect pet food ingredients imported from all countries.

“Our food supply has been put at risk by contaminated ingredients that originated overseas and were never inspected by the FDA,” the Senators charged in their letter. “The FDA owes the American public their best effort to prevent contaminated food from getting to store shelves and to remove contaminated food that is already on shelves before more pets die.”

Sources: Karen Roebuck, “Humans at risk from tainted pet food?”, Pittsburgh Tribune-Review, April 20, 2007; Susan Heavey, “FDA examines if pet food contaminant in human food,” Reuters, April 25, 2007; Nikhil Swaminathan, “Were our Pets Deliberately Poisoned?” ScientificAmerican.com, April 25, 2007; Richard J. Durbin and Maria E. Cantwell, “Durbin, Cantwell Ask FDA to Strengthen Inspections and Disclose Companies That Purchased Contaminated Rice Protein from China,” durbin.senate.gov, April 23, 2007; Victoria J. Sharp, “Urinary Obstruction,” University of Iowa Department of Urology Health Topics, March 2006, accessed April 26, 2007.