Based on its own research paper, "Toxic Chemicals in Computers Exposed", the activists claimed that when compared with other notebook computers made by four world-class companies, the HP product contained the highest level of toxic chemicals.

Tests found a high level of PBDEs, which is a class of brominated flame retardant.

"We don't know if this would directly harm computer users, but they harm the environment as it cannot be recycled and would be left as toxic waste," said Kittikhun Kittiaram, toxins campaigner for Greenpeace Southeast Asia.

Kittikhun said all of the five notebook computers were bought in Denmark in March this year and an independent laboratory was assigned to conduct the tests. The result showed that HP's notebook had the highest level of decaBDE at 1,600 milligrams a kilogram. Another branded notebook only contained 85 mg/kg of the hazardous substance, Kittikhun said.

The HP computer was also the only one found to contain lead, he said.

According to Greenpeace, HP once stated in its website that the decaBDE had been removed from its products many years ago.

"It proves that the company is lying about its products," Kittikhun alleged.

HP did not directly deny the accusation, but released a statement saying it had eliminated more than 95 per cent of brominated flame retardants used in the external case parts of its products more than 10 years ago. The company said it would work to replace others with alternatives that would not present health or environmental risks.