Two years have passed since the Deepwater Horizon drilling rig exploded, belching petroleum into the shimmering Gulf Coast for three months and causing the world’s largest accidental marine oil spill. Flames from the drilling platform have since been dowsed. The wreckage has sunk to a watery graveyard. Oil-smeared beaches have been raked and sifted. The pelicans have been degreased. Clumps of oily grass have been scooped out of fragile marshes. Reporters have long since filed their stories and returned home. Even the President went swimming in the Gulf. Life is back to normal.
Or is it?
That’s a question Kim Anderson is trying to answer. Since May 2010, the chemist from Oregon State University has been sampling chemicals and testing the toxicity of the air and water along the coast. Her findings will give public officials and ecologists a better understanding of how the spill might affect the health of humans and marine life.
“I don’t want us to abandon the Gulf just because things look like they are returning to normal. I want to make sure that they are normal,” Anderson says. “We know that the oil did not go away. It was not all physically collected and removed.”
Where do 200 million gallons of oil go? Some of it evaporates in the air. Some dissolves in the water. Some is mopped up by nature’s janitors, bacteria that nosh on oil hydrocarbons then poop out carbon dioxide. Some is coughed up on the beach in the form of black, sticky tarballs. Some gets trapped as mucky sludge in spongy marshes. Some hovers in the ocean as plumes. And, unlike the lighter vegetable oil in salad dressing that floats on top of vinegar, some of it sinks to the ocean floor, becoming an oily carpet.
It’s the dissolved and vaporized oil that Anderson has in her crosshairs. It can’t be seen anymore, but some of the chemicals in it are still hanging around—in smaller particles, thanks in part to the dispersants that cleanup crews sprayed over the seawater to break the oil into droplets. In an unfortunate side effect, this process of degradation can turn some of the chemicals into even more toxic ones. Now some of these chemicals are more easily absorbed by fish, shrimp, and filter-feeding oysters, which end up on our tables. Or the chemicals can travel into our lungs.
Anderson, who works in OSU’s Environmental and Molecular Toxicology Department, has turned her attention to polycyclic aromatic hydrocarbons (PAHs), a not-so-friendly family of more than 100 chemicals, some of which cause cancer. They can also produce nausea, vomiting, diarrhea, confusion, and skin and eye irritation—conditions that have bothered cleanup workers.
Within three weeks of the April 2010 spill, Anderson’s research team flew to the Gulf, lugging stainless steel air and water samplers. As if setting out crab pots, they lowered cage-like cylinders into the water off four piers in Alabama, Florida, Louisiana, and Mississippi, and strapped boxy, T-shaped air samplers to the piers. The simple-looking contraptions seem unbelievably low-tech—like something you could make with materials from a hardware store—but they’re designed to mimic a living, breathing body. A fish, for example, swimming in greasy water for weeks, or a person breathing oil fumes day after day. The key is a translucent, plastic ribbon that’s threaded through these metal mannequins in a series of switchbacks. An inch wide, several feet long and containing special chemicals, this strip simulates a cell membrane that lets contaminants pass through. Chemicals accumulate in the ribbon much like they would in the tissue of, say, an oyster.
The researchers collected baseline samples in May 2010 before oil began washing ashore. Then, starting in June, they left the devices on the piers for consecutive month-long periods over the course of a year, with the exception of a three-month break during the winter. The nearly constant presence of the samplers meant that if a tendril of oil just happened to drift by, the device would catch it. It’s a more comprehensive method than just dunking a vial into the water to take one sample.
About once a month, the researchers flew to Louisiana, then drove 350 miles along the coast to collect data and swap out the equipment. Results are beginning to show up. At the Louisiana site at Grand Isle, Anderson found that PAHs in the water peaked about a month after the spill, making the concentration 45 times what it was before the oil spill. It was the largest surge of the four sampling sites. “That’s a gigantic increase,” she says. “Having done this for 15 years, I’ve never seen or heard of such an increase in my career.”
In Gulfport, Mississippi, PAHs doubled about a month after the explosion and returned to approximately pre-spill levels in August. In Gulf Breeze, Florida, PAHs didn’t increase significantly until four months after the blowout, when they tripled. This was likely, Anderson says, because the sampling site was on the inside edge of a peninsula in Pensacola Bay so it took longer for the oil to creep in there. Although a two- or threefold increase might not seem like much, she says, it is significant. That’s because PAHs accumulate in organisms, so modest increases in the air and water can add up inside a body, she says.
In Gulf Shores, Alabama, the concentration of PAHs doubled and peaked five months after the catastrophe, recovered to approximately pre-spill levels by March 2011, then shot up again during the following two months. Anderson says it’s possible that severe weather there in April 2011 may have churned up oil from the seafloor. “It looks like some of the oil can come back ashore depending on weather,” she says.
Although total PAHs at three of the four sites returned to pre-spill levels by the end of the yearlong sampling period, the concentrations of the 33 individual PAHs were not the same as before, Anderson says. This is important because PAHs have different toxicities. It could be that there are now higher levels of the more dangerous ones, or just the opposite.
Back at the lab, Anderson’s researchers tested the toxicity of the PAHs. They immersed about 8,000 transparent zebrafish embryos in four different concentrations of the water pollutants they collected to see if the concentrations were actually toxic enough to do physical damage. They used zebrafish, the aquatic equivalent of lab rats, because they share many genes with humans, they grow quickly, and they’re initially transparent so it’s easy to see deformities. The researchers are analyzing the data to learn what dosage will kill the fish or cause defects such as swollen yolk sacs, accumulation of fluid around the heart, and wavy notochords, a kind of primitive backbone.
In October, several of Anderson’s graduate students returned to the Gulf to sample the air and water in all four sites again and to expand their testing to include sampling soil in Alabama. They wanted to see if contaminated sediments are getting stirred up and rousing the PAHs. Additionally, they used different equipment this time so they could capture oxygenated PAHs, which form when PAHs are broken down by sunlight and other processes. Some of these derivatives are thought to be more toxic than their parents.
The oil sheens have faded just like our ugly memories of the spill, but for OSU’s researchers, questions remain. Is the sediment harboring PAHs that show up later in the water? Are storms awakening PAHs from the seafloor? How toxic are they? How does their toxicity change over time and from site to site? Is there a risk to human health? And of course, are PAH levels back to normal?
“It wasn’t a happy story initially,” Anderson says. “But all of us were encouraged that the oil initially seemed to be dissipating faster than we could have hoped. Now we’re just trying to make sure that that story stays on a happy note.”
For more information, see OSU's Superfund Research Center's website.