A cancer-inducing chemical compound, up to 31 times the allowable limit in meat, was found in all 47 samples of edible bird's nest sold in Hong Kong, but scientists said that long-time immersion in water and boiling it could remove most of the chemical, making the delicacy safe to eat.

After comparing 47 samples of edible bird's nest sold in Hong Kong and imported from Indonesia, Malaysia, Thailand and Vietnam with natural ones in Malaysia and Indonesia, equal amount of nitrite was detected, according to tests conducted by the Hong Kong University of Science & Technology.

Besides ordinary white cubilose, the samples also contained red and yellow cubilose, considered rare varieties. They come from nests built on rock cliffs, with the mineral elements on the cliffs permeating the nests, coloring them red or yellow, the locally based Sing Tao Daily reported yesterday.

Edible bird's nest, mostly made of secretion from the salivary glands of birds, is an expensive delicacy and has been used in Chinese cooking for hundreds of years.

The nitrite level varied from 5 milligrams to 6,400 milligrams per kilogram, according to Karl Tsim, a professor with the Division of Life Science of HKUST, who led the study.

Although the region doesn't have a standard for nitrite levels in edible bird's nest, about 50 percent of the samples were discovered to exceed the limit set for meat products, with one containing 31 times the standard.

But Tsim pointed out that by submerging the bird's nest in water for three to 15 hours, rinsing repeatedly and boiling them for half an hour to 2 hours, over 97 percent of the chemical can be removed.

Nitrite was found in local samples and natural ones, meaning the chemical was not added during production, Tsim told the newspaper. He said it may be birds' excrement contaminating the nests.

Michael Lam, a professor with City University of Hong Kong, said that although water could wash away the compound, long-term consumption could still compromise the function of red blood cells. If combined with acid, nitrite could even lead to cancer, the report said.

Shanghai officials are investigating the ingredient of the bird's nest soup made of red cubilose in local markets after tests in Zhejiang Province found it was not only counterfeit but contained nitrite.