They all look so tempting but almost 80 per cent of them are tainted with toxic substances posing grave danger to the public health, say health experts.

Professor Dr Golum Mowlah of the Institute of Nutrition and Food Sciences, Dhaka University, said these fruits are artificially ripened using a chemical called ethylene oxide. It is a type of plant hormone.

In bananas, calcium carbide is used for quick ripening, Dr Mowlah said. After 5 to 6 hours of applying the chemicals, the green bitter bananas look delectable. Mangoes and other fruits take a little longer to ripen.

"After using ethylene, green fruits look ripe and attractive due to a bio-chemical reaction. But the fruits remain raw inside in most of the cases," he added. "Artificially ripened fruits do not taste good, which means the nutrition value decreased."

Vendors blame wholesale traders for the use of chemicals. Zafarullah, a fruit vendor at Karwar Bazar, said, "I have heard about the use of chemicals in fruits but I don't know whether the fruits I'm selling have it or not."

"We buy ripe fruits from wholesale traders and just sell them," he added.

However, another fruit seller said use of chemicals has decreased to a certain level due to recent drives of mobile courts.

Dr MA Sobhan, research consultant, Policy Research for Development Alternative (UBINIG), said wholesale traders are mainly responsible for the use of chemicals. They try to hasten the ripening process so they can speed up the sale.

"Weak laws are the main reason why the practice escalated to such an extreme level. However, in the context of recent political situation and drives conducted by mobile courts many businessmen are refraining from this unethical practice to some extent. Most sellers in the fruit markets seem aware of the ill effect that chemicals have.

Sobhan said that all ripe fruits produce ethylene oxide naturally. But the chemicals used for quick ripening of fruits are very harmful. Calcium carbide is extremely hazardous to human body because it contains traces of arsenic and phosphorous.

"Regular intake of chemicals like ethylene or carbide can cause irritation in the digestive tract that eventually turns into peptic ulcer. It can also cause diarrhoea, jaundice and liver failure," said Professor Mobin Khan, specialist, Liver & Medicine, Bangabandhu Sheikh Mujib Medical University (BSMMU).

Existence of excessive ethylene in food can even cause cancer, he said.

Ethylene enters the bloodstream if someone breathes air containing mists or vapours with the compound. It can also enter bloodstream through skin. So the traders or sprayers who spray the chemicals can also get lung cancer, damaged eye membrane and also asthma.

"It would be wise to wash the fruit properly and peal it before eating," Khan said.

Magistrate Rokon-ud Dowlah told Star City that since summer fruits have just arrived in the market his mobile court has started a crackdown on the use of chemicals. Last Thursday the court visited Karwan Bazar and sentenced three fruit vendors to six months' jail and collected Tk 1.5 lakh as fine for using chemicals in fruits.

The magistrate said that use of chemicals and toxic colour in fruits can be punished under Bangladesh Pure Food (Amendment) Bill, 2005. Highest penalty under section 44 (7A) is Tk. 50,000 fine or one-year rigorous imprisonment or both. For the same offence second time punishment is Tk 2 lakh fine or 2 years' jail or both.