The sediment has been polluted over the years with industrial chemicals and heavy metals, said Subra, who tested the sediment for the Southern Mutual Help Association, a nonprofit organization in New Iberia, Louisiana.
"These water bodies have received industrial wastes for decades,'' she said. "This material has toxic chemicals, metals, and organic petrochemicals.''
Matters have only been made worse by multiple oil spills caused by Katrina and Rita. According to the U.S. Coast Guard, 11 oil spills have occurred in southern Louisiana, totaling 7.4 million gallons (28 million liters) of oil, most of which has been contained.
Bacteria levels are also especially high in the Plaquemines sludge, said Rodney Mallett, spokesperson for the Louisiana Department of Environmental Quality.
"The sewage treatment plants were underwater," he explained. "Between the animal waste and the human waste, you've got a lot of bacteria.''
Health and environmental agencies are advising people to avoid contact with the sludge. They recommend that people wear gloves, goggles, and dust masks, and that they wash promptly if exposure occurs.
EPA officials are directing people to its Web site (www.epa.gov) to inform themselves of the contamination risks.
But most people returning to the area don't have computers to get that information, said Erik Olson, an attorney for the Natural Resources Defense Council, an environmental advocacy group.
"If you [do] read the Web site," he added, "you practically have to have a degree in chemistry to understand it."
To better inform people of health risks, the Southern Mutual Help Association and Oxfam America are developing a program to give every returning resident a protective kit.
Each kit would contain waterproof suits, goggles, shoe covers, and masks, along with information about potential hazards. Volunteers would give out the kits at the security checkpoints that now stand at the major entrances to affected cities.
The groups have made a hundred demonstration kits, which cost about $100 (U.S.) each to produce, and have shown them to state leaders in Louisiana.
"The governor is really in favor of this," Subra said. "We just have to determine how we're going to fund them.''
Toxic Mold Blooms
In addition to the toxic sediment, sprawling blooms of mold have now taken hold in many flooded homes. "The mold is growing everywherehomes are just coated with it,'' Subra said.
The problem has become so widespread that federal health officials warned Wednesday of allergic reactions and toxic responses to the mold. Professionals should be hired to clean mold that covers more than ten square feet (one square meter), they urged.
"Those [surfaces] that can't be cleaned need to be removed," said Steven Redd, chief of the Air Pollution and Respiratory Health Branch of the U.S. Centers for Disease Control and Prevention (CDC).
The effects of the mold are already surfacing in Mississippi, where respiratory problems are among the illnesses doctors there are reporting.
"We're seeing a lot of asthma from inhaling the mold,'' said Richard Paat, team leader of a temporary East Biloxi clinic. "And mouth sores from the bad water."
Due to contact with unclean water, 33 people in the flood zone have contracted Vibrio infections, according to the CDC. The infections are caused by a family of bacteria that live in contaminated salt water. They can cause serious illness, especially in people with compromised immune systems.
To date, six people have died from Vibrio infections.
"People had open wounds and walked through floodwater with sewage in it," CDC spokesperson Von Roebuck said. "And these folks were having these wounds infected with Vibrio.''
Disaster Response Care
"This is a highly contaminated area,'' said Susan Briggs, the physician overseeing FEMA's disaster-response medical teams in Louisiana and Alabama.
Her teams have been inoculating residents for tetanus and Hepatitis A and B. Hepatitis is a danger when people are exposed to sewage, through water or food, Briggs explained. Tetanus can occur when people cut themselves on unclean materials, as may happen when cleaning debris.
The rudimentary living conditions in many Katrina-struck areas make it more likely that people will get sick and injured, Briggs said.
"They have no electricity, no clean water, no air conditioning," she said. "There are collapsed structures and stray animals. There are huge amounts of stray dogs, and people have been bitten."
Briggs and other doctors in the area have been treating many cases of diarrhea, rashes, and upper-respiratory illnesses.
All of these conditions are to be expected after natural disasters, according to the CDC. But it's too soon to know if these ailments are related to contamination, the CDC's Roebuck said.
"We're looking at that question," he said. "We'd like to know the answer."
Free E-Mail News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES