In the United States, it is feared as a killer of cats and dogs and a potential threat to humans.Yet in China, the mildly toxic chemical melamine is commonly used in animal feed and is even praised by some customers.
"Using the proper quantity of melamine will not harm the animals," said Wang Jianhui, manager of the Kaiyuan Protein Feed company in the northern city of Shijiazhuang. "Our products are very safe, for sure," Wang added.
Feeding animals food containing melamine risks introducing the chemical into the food chain through their meat or eggs. Scientists say there is no evidence that people could get sick, but say they know too little about how the chemical reacts with other substances to be sure it is safe.
Chinese wheat gluten containing melamine was blamed in a wave of pet deaths in March due to kidney failure. The U.S. Food and Drug Administration investigated, and nearly 100 brands of pet food made with the ingredient were ordered recalled. Adding the chemical to food is illegal under American law, and China's government last week said it was banning its use in food products.
Usually used to make fertilizer and plastics, melamine has no nutritional value but is rich in nitrogen, meaning it raises the nitrogen level of feed. That makes products appear to be higher in protein, and can lead to higher prices for feed for stock animals such as pigs, chickens, and fish, as well as for household pets such as cats and dogs.
James Kapin, a member of the American Chemical Society's executive committee on health and safety, said testing on rats and mice has shown melamine to be toxic only at extraordinarily high levels.
However, he said manufacturing the pet food or the animals' own metabolism may have changed the melamine into something more lethal. Maybe a "combination of all these things," he said, explains why relatively low doses of melamine resulted in kidney failure.
In the past, Kapin said testing for nitrogen was a "quick and dirty way to screen for protein." He said several companies have said they would no longer rely on nitrogen tests to determine protein content, and instead would do more expensive tests that look for protein itself.
However, Kaiyuan Protein Feed's Wang said his customers either don't know or aren't concerned about the melamine.
"We've been running the melamine feed business for about 15 years and receiving positive responses from our customers," Wang told The Associated Press.
Some pet food was shipped to hog farms in several U.S. states for use as feed and was later discovered to have another ingredient, rice protein concentrate, that had been imported from China and was tainted with melamine. Thousands of U.S. hogs that were fed contaminated feed were ordered destroyed to prevent adulterated meat from reaching consumers.
The contaminated gluten was traced to a trading company based in eastern Jiangsu province, Xuzhou Anying Biologic Technology Development Co., and a firm in the nearby province of Shandong, Binzhou Futian Bio-technology Co. The U.S. Food and Drug Administration has blocked wheat and rice gluten from both companies pending an investigation.
China's government said last week it would allow FDA investigators to visit.
Xuzhou Anying managers have said they have no idea how the melamine got into the gluten, which they claim was acquired from other firms and sold to a third company which exported it to the United States.
However, suspicions were raised when the company was found to have posted an online advertisement in March seeking to buy melamine.
Ji Denghui, manager of Sanming Dinghui Chemical Trading Co. in the eastern province of Fujian, said animal food companies are some of his best customers.
"A lot of animal food companies buy melamine from us to add in the animal feed," Ji said. "This can lower the production cost and increase nitrogen levels."
Ji played down the risk, saying that despite China's repeated food safety scares, the companies could be trusted to use melamine safely.
"I believe it won't do any harm if there is only very small amount," Ji said. "Otherwise, those companies could not do that."