Laboratory studies of melamine-fed catfish, trout, tilapia and salmon by the FDA's Animal Drugs Research Center found that fish tissues had melamine concentrations of up to 200 parts per million. That's 80 times the maximum "tolerable" amount set by the FDA for safe consumption.
Iddya Karunasagar, a United Nations fish-product safety expert in Rome, said the FDA's research suggested fish would have to ingest large amounts of melamine to pose a health threat to humans, something that he considered unlikely. But he said there were no data on melamine levels in Chinese-produced fish and animal feed.
Other scientists said testing of melamine in farm-raised fish from China should be made mandatory because of the dearth of information about melamine levels in Chinese feed and fish.
"That's the problem; no one has a clue how much concentration and for how long" fish from China have ingested melamine, said Jim Riviere, director of chemical toxicology research at North Carolina State University in Raleigh. "There's an issue of relative human safety," he said. "It would be prudent to screen for melamine."
An FDA representative in Washington wouldn't comment on why Chinese-produced seafood didn't have to be analyzed for melamine when imported to the U.S. Nor were FDA researchers made available to comment on their agency's findings, reported recently in the Journal of Agricultural and Food Chemistry.
Research undertaken by Riviere and others show that melamine in feed consumed by pigs and cows is excreted in the urine or otherwise flushed out, leaving virtually no trace of it in the muscle or meat of the animals. But fish appear to be different, toxicologists say.
Fang Shijun, who has monitored the melamine problem for several years, says he believes that the adulterated products are being supplied only by small operators, which abound in China.
Like those who added melamine to milk and diluted it with water to increase profit, feed businesses can sell more by substituting melamine for real protein sources, especially with the cost of corn and other raw materials having soared in the last couple of years.
"It is impossible to calculate how many of them have done that," said Fang, manager of feed research at Shanghai EFeedLink Information Technology, an agriculture consulting and research firm.
