Experts say that some shrimp originating in Tianjin have been injected with gelatin-like chemicals to make them heavier and plumper, posing a threat to public health.

The transparent chemical can usually be found in the heads of the shrimp. A local wholesaler, who declined to reveal his name, told Xinhua that the altered shrimp were frozen, and the gelatin-like chemical was injected to increase the weight.

"The frozen shrimp tend to shrivel after being taken out of the freezer, so lots of shrimp are injected with gelatin-like chemicals in the head and torso," he said.

Wang Shuo, vice president of the Tianjin University of Science and Technology, told the Global Times that if it is confirmed the chemical is a gelatin, it may be harmful to people's health.

"There are two kinds of gelatin. One is edible, and used as a food additive. The other is used in industrial products, which contains a certain amount of heavy metal, and thus poses a health threat," Wang said.

"Since the identity of the chemical has not been confirmed I'm not sure if it is hazardous, but adding such chemicals is definitely against the law," he added.

Li Zhiyong, an official from the local food safety committee, refused to make any comment on the issue over the phone with the Global Times, but he told the Xinhua News Agency that the altered shrimp have been an issue for a long time.

"Such shrimp have long plagued our city. In 2005, we raided a workshop and ordered 20 tons of shrimp be disposed of," Li told Xinhua.

To tackle this food safety problem, people should not only depend on the supervision and regulation departments, but also improve the integrity of seafood dealers, Wang told the Global Times.

"The seafood market has always been chaotic, and it is difficult for related regulatory departments to control," said Shang Tun, a Tianjin resident.

"After I heard about the altered shrimp, I made the decision not to eat shrimp in the future,"she said.

Under pressure from the public, the Tianjin Administration for Trade and Commerce launched a 10-day campaign on Wednesday to seize the problematic stock of shrimp in local seafood markets, Xinhua reported.