Duck eggs containing a poisonous red dye that had been imported from neighbouring Hebei Province were taken off shelves in Beijing this weekend, triggering concerns over food safety.

Duck eggs Duck eggs containing a poisonous red dye remains on sale in a farmers' market in Beijing Monday. [newsphoto]

Officials at the Chinese Institute of Food Science and Technology have confirmed that the Baiyangdian brand eggs contained Sudan Red IV, a carcinogenic industrial dye used to make shoe polish, among other goods. The dye had been added to the duck's feed to make the yolks of their eggs more red, according to a report on CCTV.

The Beijing Administration for Industry and Commerce is currently testing salted duck eggs in local markets around the city for traces of the poisonous dye.

The results of the administration's investigation will be published when it completes the tests, a spokeswoman for administration who gave her surname as Wang told China Daily yesterday.

Meanwhile, a food-safety expert said the public should not panic.

"Technologies allowing us to test food safety are getting more and more advanced," said Wu Yongning, director of the Chemistry Lab of Food Nutrition and Safety Institute, under the Chinese Centre for Disease Control and Prevention.

He said food-safety standards in China are actually improving. The expert also said that just because some food contains traces of carcinogens does not mean that food is in itself dangerous.

"Only large accumulations of such substances can cause cancer," he said. "But we have to limit the presence of potentially harmful substances to an acceptable amount."

Sudan IV is an industrial dye used mainly to make shoeshine, flooring and candles. It is a Grade-III carcinogenic substance that is listed as a cancer-causing agent by international cancer-research organizations.

The official investigation has shown that the tainted eggs contained as much as 0.137 mg Sudan IV per kilogram of eggs.

Salted duck eggs with red yolks are commonly thought to be more nutritious than eggs with yellow yolks and are usually more expensive. Some people think that the eggs become red when ducks eat large amounts of fish and shrimp.

Baiyangdian Lake is the largest freshwater lake in Hebei, making very suitable for raising ducks.

"Baiyangdian brand eggs are very popular in Beijing. We can sell 3,200 kilograms a day," an official from a local egg processing plant told CCTV reporters.

Those eggs were sold to local Hebei people as well as to some duck-egg processing factories in Beijing.

In Hebei's Anxin County, the source of the poisonous eggs, local government officials have seized duck eggs suspected of containing the poisonous dye.