Up to 400,000 New Yorkers breathed in the most toxic polluting cloud ever recorded after the twin towers were brought down three years ago, but no proper effort has been made to find out how their health has been affected, according to an official report.
The US government study provides the latest evidence of a systematic cover-up of the health toll from pollution after the September 11 disaster, which doctors fear will cause more deaths than the attacks themselves.
The Bush administration suppressed evidence of increasing danger and officially announced that the air around the felled buildings was "safe to breathe".
Another report reveals that it has since failed at least a dozen times to correct its assurances, even when it became clear that people were becoming sick.
The official report - sent to Congress last week by the US Government Accountability Office - says that between 250,000 and 400,000 people in lower Manhattan were exposed to the pollution on 11 September 2001.
But it shows that the government has yet to make a comprehensive effort to study the effects on their health. And it reveals that there is no systematic effort to adequately monitor the well-being of those affected, give them physical examinations or provide treatment.
Scientific studies have shown that the cloud of pulverised debris from the skyscrapers was uniquely dangerous.
The US government's own figures show that it contained the highest levels of deadly dioxins ever recorded - about 1,500 times normal levels. Unprecedented levels of acids, sulphur, fine particles, heavy metals and other dangerous materials were also measured. Asbestos was found at 27 times acceptable levels, and scientists found about 400 organic alkanes, phthalates and polyaromatic hydrocarbons - many suspected of causing cancer and other long-term diseases.
The site at Ground Zero went on smouldering, becoming what scientists describe as a "chemical factory", creating new dangerous substances.
