This year's Dragon Boat Festival falls on Wednesday, the fifth day of the fifth lunar month, and along with paddling frantically across your local lake, eating zongzi is the big tradition of the day.

Zongzi is a pyramid-shaped glutinous rice dumpling wrapped in green bamboo or reed leaves, and filled with red bean paste.

However, be careful when you open the green-leaf wrapping this year, warnings have been issued by the China Consumer Association of fake leaves containing excessive amounts of chemicals.

Experts from the association have confirmed that chemicals such as copper sulfate and copper chloride, used by some manufacturers to turn or to keep the leaves green, are harmful to health.

Shen Xiangkun, an expert from the Henan Food Research Institute, said the practice is a serious violation of the Food Hygiene Law, which bans any industrial material from being used as a food additive.

"The leaves dyed with copper sulfate or copper chloride contain some metal elements which will penetrate into the zongzi and cause great damage to the health. The worst chemicals might lead to cancer or renal failure," Shen said

"The bamboo or reed leaves used to wrap zongzi are fresh and green when freshly picked but will gradually turn yellowish green or yellowish brown after a period of time," Shen explained.

According to a random examination carried out by food safety authorities in Yuyao, a city in east China's Zhejiang Province, earlier this month, the illegal practice of dyeing zongzi leaves is widespread.

The city's food authorities selected four types of zongzi produced by three local factories and found that three of them contain excessive amounts of copper. The most contaminated zongzi contained 34 times more copper than the national standard.

Experts from the association suggested customers go to regular supermarkets or stores to buy zongzi made by established manufacturers.

They also offered three tips on how to tell if a zongzi is contaminated:

Appearance: Contaminated zongzi leaves look fresh and green, while normal ones are dark.

Odor: Dyed zongzi leaves smell different from real leaves after boiling. They give off a mildly sulfuric odor.

Color of boiled water: The water used to boil contaminated zongzi will turn green after boiling, while normal zongzi water turns yellowish.

The Dragon Boat Festival, also called Duanwu Jie, is one of the most important traditional Chinese festivals. People eat zongzi and race dragon boats in memory of the ancient patriot, Qu Yuan, who lived during the Warring States Period (475 - 221 BC).

(China Daily May 29, 2006)