Flooding in the aftermath of hurricane Katrina caused arsenic levels to soar in New Orleans, according to a report due to be published in Environmental Research.

 

US authorities said high levels of arsenic found in floodwater sediment after the flooding was down to pre-existing contamination. But the new findings refute this claim.

 

“The contamination of sediments with arsenic should have been investigated and addressed in the context of hurricane recovery to ensure public health and safety during the rebuilding process,” says lead author Miriam Rotkin-Ellman, from the Natural Resources Defence Council in California, USA. “Arsenic is toxic to humans… no amount is considered safe.”

 

Long-term exposure to arsenic can raise the risk of bladder, skin and lung cancer. There is also evidence to suggest the toxic metal contributes to high blood pressure, cardiovascular disease, diabetes, and problems with the reproductive system. But the health risks of exposure to low levels of toxic metals in the environment remain unclear.

 

The researchers recorded arsenic levels in soil samples from 70 different parts of the city, collected in 2005 and 2006 after the city flooded. They compared these with the levels seen in archived soil specimens collected five to eight years earlier from roughly the same parts of the city. Contamination levels after the hurricane were 50 times higher than levels that would prompt cancer screening in exposed people, they say.

 

“The concentration of arsenic in the post-Katrina soil samples was consistently and significantly higher than location-matched post-Katrina sediment samples taken within the 1-year aftermath of flooding,” they write.

 

Additional soil tests done in 2007 showed that the level of arsenic has fallen substantially since in many parts of the city, but not everywhere. The contamination remained above pre-flooding levels in 30% of locations tested, say Rotkin-Ellman and colleagues.

 

Marjorie Aelion, of the University of Massachusetts, says that the arsenic would have been washed away by rain and wind in the time between testing. “Some of the arsenic could still be in the soil… at a lower depth,” she adds. “It eventually could travel to ground water but I think that would take a long time, and be unlikely at this point in time.”

 

In some areas, the soil was treated to remove the contaminant, adds Rotkin-Ellman, but in others it probably washed into low-lying areas or storm drains. “We remain concerned about these sites, because… we don’t know if the arsenic was just moved around and presents a future health risk.”

 

The latest round of tests revealed that schools and playgrounds had high levels of contamination in 2007. But there was no record of arsenic levels prior to flooding in these areas, so the extent to which the disaster contributed to this contamination is unknown. Children are especially vulnerable to the toxic effects of the contaminant as their bodies are still developing. They are also more likely to come into contact with the metal when they play on the ground and put their hands in their mouths.

 

It is not clear where the added arsenic came from, say the authors. One theory suggests it may have washed off wood treated with an arsenic-containing preservative that was commonly used in the region until US authorities banned it several years ago on toxicity grounds.

 

Aelion believes this wood preservative could play a part in the contamination, but it would contribute only a small amount to the total level of arsenic seen after the disaster. It is likely that arsenic-contaminated sediment was pulled up along with water from nearby Lake Pontchartrain when the city flooded, she says. “New Orleans has a history of environmental contamination and once an area is contaminated, it is extremely difficult for that area to be cleaned up.”

 

Rotkin-Ellman says this kind of threat should be considered in preparedness for future disasters. “These plans should seek to prevent the migration of contaminants from industrial and hazardous waste pollutant sources and protect drinking water resources.”