NEW ORLEANS -- There are effects from the oil spill that you can see, like oil washing ashore, and those that you can't, like when oil compounds breakdown and go airborne.
"We don't want to be alarmist, but we want to be realistic," said Marylee Orr, with the Louisiana Environmental Action Network, an advocacy group.
For several weeks now, the federal Environmental Protection Agency has been tracking what's in the air, by using a mobile truck and seven monitoring stations, located mainly in St. Bernard and Plaquemines Parishes.
They are looking for evidence of several compounds, including Hydrogen Sulfide, particulate matter and Volatile Organic Compounds (VOC's), like Benzene, a known carcinogen.
"These pollutants could pose a health risk to local communities and this monitoring is essential to ensure that communities are protected as BP takes direct response actions," EPA Administrator Lisa Jackson said during a Senate Committee Hearing on Tuesday.
All can irritate the eyes, nose, throat and lungs, and in some cases lead to nausea and dizziness.
So what have they found? Some elevated levels, but not every day and not for long periods of time.
"The levels have not been that high. Is it something we want out there? Absolutely not. But it's pretty far offshore," said Luann White, director of the Tulane Center for Applied Environmental Public Health.
Take Hydrogen Sulfide, commonly known as swamp gas: a normal level in the air for it ranges from 5 to 10 parts per billion (ppb). At monitoring station in Venice, on May 2, the levels recorded were 30 ppb. The next day, May 3, the reading was nearly 40 times that, at 1,192 ppb. The day after that, May 4, it dropped down to 46 ppb, before rising on May 5 to 1,010 ppb.
"It varies based on the wind direction, whether or not they're burning the slick," Orr said. "I think what they're saying is that it's an OK exposure for a short amount of time -- and we have a concern about that sort of exposure for any amount of time."
However, Wilma Subra, a chemist who heads up a lab and environmental consulting firm in New Iberia, said the numbers she's been analyzing give her pause.
"They're there at a little over the levels that you would expect to start getting those health impacts," Subra said. "So, that is of concern, that the people understand what is there and understand if they start getting the health impacts, they should take precautions to move out of the area."
Those who should pay particular attention are the young, the elderly or those who already have underlying breathing problems. Experts said anyone experiencing symptoms of exposure to those chemicals, should see their doctor.