After the terrorist attacks of 11 September 2001, the US Environmental Protection Agency (EPA) took some flak for declaring, perhaps prematurely, that the air was safe in the vicinity of the World Trade Center in New York.

Now the agency, which is charged with protecting public health and the environment, is abdicating its responsibility to issue clear public guidance on possible health hazards in New Orleans, flooded last month by Hurricane Katrina. It is saying nothing on the advisability of returning to the ruined city, arguing instead that its job is just to run tests and pass on data to local officials, who will make of them what they will.

For what was once the world's foremost environmental agency, this simply isn't good enough. The EPA's own scientific advisory board, as well as the usual welter of environmental groups, are rightly calling on the agency to do its job properly, and give the American people more solid information about the environmental risks posed by episodes such as the flooding after Hurricane Katrina (see Advisers knock Katrina health tests).

Members of the science advisory board are unhappy with the tests that were carried out in the first days, when the city was still under water. Tests were done for many regulated chemicals, but those for more obvious threats, such as disease-causing microbes, were not. According to Granger Morgan, a technology policy expert at Carnegie Mellon University in Pittsburgh and chairman of the EPA science advisory board, the agency needs to prepare better plans for specific emergency situations, so that it can respond appropriately.

EPA needs to be prepared to assert its opinion and judgment on matters that impact human health and the environment, regardless of who else is involved.

Most of the data currently being collected by the agency on the ground in New Orleans pertain only to short-term risks. Levels of metals or pesticides in the sediment left behind as the floodwater receded are being compared with exposures that are safe for a few days, or even less. People who want to find out whether the levels of contaminants near their homes are dangerous in the longer term will have to do their own research.

The agency can hardly be accused of sitting around twiddling its thumbs in New Orleans. It has more than 1,000 employees working in the ravaged track of the storm, and is doing its best to advise members of public about how best to protect themselves from contaminants. Hundreds of measurements have been carefully posted on its website (http://www.epa.gov/katrina). All of this has been done within the agency's existing and rather overstretched budget.

People are moving back into New Orleans now, pushing their way into mud-caked buildings, sleeping in rotting, oily houses, and scrubbing mould off the walls without wearing protection — or, in at least one case, with respirators gamely strapped on upside-down.

Naturally, the political pressure to repopulate the area is intense. There is nothing to suggest that the city should be declared uninhabitable. But the public deserves much more than statements such as one issued on 17 September, to the effect that neither the EPA nor the Centers for Disease Control and Prevention in Atlanta, Georgia, will come forward to offer any guidance on the reinhabitation of New Orleans.

As the EPA's own inspector-general declared in 2003: “EPA needs to be prepared to assert its opinion and judgment on matters that impact human health and the environment, regardless of who else is involved or may share responsibility. Ultimately, the public, Congress, and others expect EPA to monitor and resolve environmental issues.” In the wake of Katrina, the need for the agency to fulfil that role is clearer than ever.