More than 40 percent of companies producing disposable lunch boxes for the Beijing market are supplying inferior and possibly dangerous products, according to a recent survey.

Dong Jinshi, executive vice-president of the International Food Packaging Association, a Hong Kong-based non-government organization, said at a press conference held in the capital on Wednesday that among 17 disposable box manufacturers they probed, only 10 were producing quality products.

The 17 companies are responsible for 80 percent of lunch boxes sold in the city.

One of the 17 producers was found to still be selling foam lunch boxes, which have been banned since 2001.

China Central Television reported in 1999 that foam lunch boxes release toxic substances, including dioxins - a highly toxic compound - after they are heated to more than 65 C.

The association reported its findings to the Beijing bureau of quality and technical supervision. The bureau quickly closed the factory making the foam lunch boxes following a raid on Tuesday - World Consumer Rights Day, Dong said.

Around 15 billion disposable lunch boxes are used nationwide every year. More than 90 percent are made of plastic, according to the association.

By the end of February, about 1,400 disposable lunch box producers had acquired licenses for production.

To conform to legal requirements, each lunch box costs around 0.15 yuan (3 cents) to produce. Some makers have resorted to using cheap toxic materials, including industrial calcium carbonate, in an attempt to keep down production costs.

The association last week commissioned a scientific research group with Beijing University of Technology to run tests on confiscated substandard disposable lunch boxes. The results found that part of the plastic content was absorbed by hot food placed in the boxes.

The association urged consumers not to store hot food in plastic disposable lunch boxes unless it has cooled.

Meanwhile, the association also announced that another of its investigations had found that napkins sold in Beijing and Tianjin municipalities and in Hebei province were beset with potential quality problems.

On Tuesday, a special annual TV program hosted by China Central Television that champions consumers' rights, disclosed that low-quality napkins, some of which were recycled from waste paper, were found to have been extensively bleached with brightener.

"Among some 40,000 restaurants in Beijing, I believe more than half of them are using the substandard napkins," said Dong.

The optical brightener was also found in paper cups sold in the three regions' markets, according to the association.

The organization's report said that, out of 16 samples collected at four open-air markets, only three were found to have clear and formal trademarks, implying the rest might have been produced without quality supervision.

Dong suggested customers buy products with clear trademarks from hypermarkets and superstores rather than low-quality ones from open-air markets.