Narrator: This is Science Today. Dozens of pet dogs and cats across the United States died last year after eating contaminated pet food traced back to China. It was a frightening episode for pet owners that led to a nationwide pet food recall. Veterinary toxicologists at the University of California, Davis were the first to identify what caused those deaths. Dr. Robert Poppenga says it was a deadly mix of two chemicals that are relatively harmless alone.

Poppenga: Initially, it was melamine that was found and then further investigation also found another chemical called cyanuric acid - very closely related chemically.

Narrator: Melamine is relatively non-toxic and is commonly used in China to boost protein content in pet food. The presence of cyanuric acid is less clear, but Poppenga says their lab found that mixed together, it quickly resulted in renal failure.

Poppenga: Now that those two compounds have been identified and characterized, the FDA has initiated a testing program and so any protein sources coming into this country I'd speculate now are being tested for these compounds.

Narrator: For Science Today, I'm Larissa Branin.