In an exclusive interview, Hugh Kaufman, an expert on toxic waste and responses to environmental disasters at the US Environmental Protection Agency (EPA), said the way the polluted water was being pumped out was increasing the danger to health.

The pollution was far worse than had been admitted, he said, because his agency was failing to take enough samples and was refusing to make public the results of those it had analysed. "Inept political hacks" running the clean-up will imperil the health of low-income migrant workers by getting them to do the work.

His intervention came as President Bush's approval ratings fell below 40 per cent for the first time. Yesterday, Britain's Deputy Prime Minister, John Prescott, turned the screw by criticising the US President's opposition to the Kyoto protocol on global warming. He compared New Orleans to island nations such as the Maldives, which are threatened by rising sea levels. Other US sources spelt out the extent of the danger from one of America's most polluted industrial areas, known locally as "Cancer Alley". The 66 chemical plants, refineries and petroleum storage depots churn out 600m lb of toxic waste each year. Other dangerous substances are in site storage tanks or at the port of New Orleans. No one knows how much pollution has escaped through damaged plants and leaking pipes into the "toxic gumbo" now drowning the city. Mr Kaufman says no one is trying to find out.

Few people are better qualified to judge the extent of the problem. Mr Kaufman, who has been with the EPA since it was founded 35 years ago, helped to set up its hazardous waste programme. After serving as chief investigator to the EPA's ombudsman, he is now senior policy analyst in its Office of Solid Wastes and Emergency Response. He said the clean-up needed to be "the most massive public works exercise ever done", adding: "It will take 10 years to get everything up and running and safe."

Mr Kaufman claimed the Bush administration was playing down the need for a clean-up: the EPA has not been included in the core White House group tackling the crisis. "Its budget has been cut and inept political hacks have been put in key positions," Mr Kaufman said. "All the money for emergency response has gone to buy guns and cowboys - which don't do anything when a hurricane hits. We were less prepared for this than we would have been on 10 September 2001."

He said the water being pumped out of the city was not being tested for pollution and would damage Lake Pontchartrain and the Mississippi river, and endanger people using it downstream.