The study, published in the November issue of the scientific journal Toxicological Sciences, identifies the principal contaminants as melamine and cyanuric acid.

Researchers at The Procter & Gamble Co. in Cincinnati and the Center for Veterinary Medicine, U.S. Food and Drug Administration in Laurel, Md., said that neither of these compounds is very toxic alone, however, when given in combination, the two compounds form a virtually insoluble complex.

This complex forms in the tubules of the kidney, blocking urine flow and causing renal failure.

The research was done in rats, but because the toxicity depends only on the two compounds being present in the kidney at the same time, is relevant to other species, including humans, the scientists said.

The study also shows that the melamine-cyanuric acid complex is soluble in acid, suggesting that acidification of the urine in the distal tubules of the kidney may be a reasonable treatment option.

The paper is available at: www.toxicology.org.