Chemical Pollutants from Deepwater Horizon Spill

by cassdaug

The Deepwater Horizon oil spill in the Gulf of Mexico back in April 2010 has left a plethora of issues for scientists to study. One major issue is simply: what happened with the pollutants from the spill?

The folks over at Skytruth.org put together a nifty interactive map-timeline that depicts almost one thousand oil incident reports around the Gulf of Mexico. These incident reports take into account: oil in the water, oil on land, oil-affected wildlife, and whether or not surrounding trash samples were coated in oil, among other categories. The categories are displayed on the map as layers, so users can turn multiple layers on or off. The map is also equipped with an adjustable timeline, so users can see what the gulf pollution looked like before Deepwater Horizon and how the area was affected afterwards. The timeline also comes with the option to “play” itself – so users can see an automated progression in the amount of oil affecting the gulf area.

Incidents are still being reported – there have been over a dozen this month alone. But the map certainly looks more clear now than it did a year ago, or even four months ago. Predictably, there are still several concerns.

For one, oil was not the only substance released into the gulf. A chemical dispersant was administered to the spill itself in hopes ofdegrading some of the oil, hoping to lessen its impact on the environment. The dispersant, however, has only been used on oil spills that occur on the surface of the ocean. The Deepwater Horizon spill ejected oil into depths of 5,000 feet below sea level.  It was unknown how the chemical would react to conditions of the deeper sea.

One study was conducted about a year ago to acquire information about the nature of the dispersant in these deeper waters. The study was led by Elizabeth Kujawinski, a chemical oceanographer at the Woods Hole Oceanographic Institution. Her findings revealed that the dispersant did not float to the surface – it remained in the deeper depths of the ocean. “We don’t know if the dispersant broke up the oil,” says Elizabeth. “We found that it didn’t go away, and that was somewhat surprising.”

One of the major components of the dispersant is a chemical called DOSS (dioctyl sodium sulfosuccinate). In May and June, DOSS was present in the plumes of oil more than 3,000 feet deep. The plume travelled southwest, carrying a mixture of oil, natural gas, and dispersant. In September, DOSS concentrations (in parts-per-billion) had decreased (WHOI, 2011).

The decrease in DOSS concentration would seem to be a good thing. However, with a new sensitive chromatographic technique developed by Kujawinski and WHOI associate Melissa C. Kido Soule, the true nature of the decrease in DOSS is exposed. In reality, there was little or no biodegradation of the dispersant. The decrease in deep-water DOSS concentrations was due to dilution – good old fashioned mixing less of one thing into more of another. So if the chemical was not absorbed or degraded in any way, it still lingers in the depths.

Kujawinski’s study is strictly concerned with the movement of DOSS concentrations, not its toxicity or overall environmental impact. However, her findings may yet spur several other studies, as the impact of the oil spill is still widely unknown.

One environmental study takes a look at Louisiana’s salt-water marshes and the impact of the oil spill there. Deepak Mishra of the Department of Geosciences and Geosystems Research Institute at Mississippi State University examined the marshes about 18 months post-spill. He and his team discovered that the amount of area with reduced biomass and canopy chlorophyll (e.g. seaweeds, sea grasses, other marine plants) rose from 50-65 km2 to over 400 km2. This means areas with fewer marine plants grew 8 times larger than before the spill. Or, areas with marine plants decreased eightfold (Mishra, 2012).

Marine ecosystems are highly complex and fragile environments, just like any other. Destruction of marine plants equates to the destruction of forests on land – loss of habitat for wildlife and also loss of prey for the predators. Potential disruptions in food chains are never a positive thing.

So on top of oil, there is a sort of chemical wildcard in the form of this dispersant. The Deepwater Horizon spill being unique, all solutions were experimental. Not only is the spill the largest at a significant depth, but also the first time the dispersant was added below the surface.

A major concern is that the map-timeline at Skytruth.org still depicts pockets of pollutants residing on the western coast of Florida, the southern coasts of Louisiana and Mississippi, and the eastern border of Texas. Whether these pollution pockets are made of dispersant, gas, oil, or any of the above – none seem welcome in coastal marine ecosystems.

This raises concerns not only with fishing industries, but with local residents and the tourism industry. Going on a fishing vacation to the Gulf may not be a great idea – habitats may have lost some biodiversity which in turn may lower the number of normal Gulf species. Beaches are probably clean and safe for the most part, but what about oil-covered trash washing up on shore?

The concern of oil spills is quite evident. Not only are oil and natural gas ejected into the surrounding ocean, but chemical dispersants are added in an effort to help. The effects of both at depth are quite unknown, but the Deepwater Horizon spill gives scientists plenty of research. With the knowledge gained from this tragic spill, perhaps we can prevent and/or deal with such an ecological disaster from occurring in the future.

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