U.S. experts say sediment left by receding floodwaters in New Orleans is contaminated and could pose health risks to returning residents.

Resident tries to clean debris from Hurricane Katrina

The Environmental Protection Agency said Friday that recent test samples from storm debris and soil revealed high levels of bacteria and fuel oil. Officials warned people to avoid contact with the contaminated materials.

U.S. experts had previously reported high levels of bacteria in the floodwaters of New Orleans. As sediment dries, they plan to conduct air sampling and assess other exposure risks.

Oil spills have been reported in New Orleans and many parts of Louisiana's southeastern coast. The U.S. Coast Guard has counted more than 40 spills from refineries, storage depots and other facilities.

The spills range in size from several hundred liters to 15 million liters.