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.

Participants wrap Zongzi during a wrapping contest as part of the Dragon Boat Festival celebrations in Beijing on Saturday. [newsphoto]

Zongzi are a glutinous rice dumpling wrapped with green bamboo or reed leaves into the shape of a pyramid, 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 sulphate and copper chloride, used by some manufacturers to turn or to keep the leaves green, are harmful to the 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 by copper sulphate 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 they have just been 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 three of them to have green leaves containing excessive amounts of copper. The worst 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 brands.

They also offered three tips to tell if a zongzi is poisonous:

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

Odour: Poisonous zongzi leaves do not have the same unique scent of normal leaves after boiling. Instead, they give off a mildly sulphuric odour.

Colour of boiled water: Water containing poisonous zongzi will turn green after boiling, while normal zongzi water turns yellowish.

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