Some fresh looking shrimp sold in the city are dipped in caustic soda to make them look healthier, which could be harmful to dinners, the Shanghai Food and Drug Administration warned yesterday.

FDA officials are warning people to be cautious when buying shrimp in seafood markets. The administration admits, however, that it is almost impossible to tell which shrimps have been dipped in caustic soda with the human eye. It isn't taking any steps to have the government outlaw the process, however.

Dipping shrimp in caustic soda can make them look fatter and glossier, a process that has been quietly used in China for decades.

While the caustic soda makes the shrimps look nicer, it also destroys the taste and some of the nutrients in the crustaceans. The shrimps will also lose their luster, shrink and give off a strange smell when they are cooked.

The FDA said treated shrimp will sometimes make people feel like they have pins and needles sticking in their mouths when eating them.

"Now we dare not sell caustic soda shrimps in public or we'll be fined. But you may leave me an address and I'll send the products to you tomorrow," a female vendor at the Hengda Aquatic Product Market in Pudong told an undercover reporter yesterday.

She said most of the treated shrimps are imported from neighboring provinces and many small restaurants in the city buy them regularly.

"Of course eating these shrimps will do harm to the human body," said Dr Li Mingyue from Baogang Hospital. "As caustic soda is an alkaline, it can burn the inside of the esophagus and stomach."

"There are two kinds of caustic soda, the edible and the industrial. Edible caustic soda is permitted to be used in manufacturing aquatic products," said Gu Zhenhua, director of the FDA. "But some people use industrial products because they are cheaper." 

According to Gu, it's hard to distinguish if the shrimps are dipped in edible or industrial caustic soda.

"We can only suggest people pay more attention to those especially good-looking products when choosing shrimps," said Gu.

(Shanghai Daily March 21, 2006)