How attempts to clear up the Deepwater Horizon spill may have made
it WORSE: Dispersant chemicals 'made oil penetrate Gulf Coast beaches
more deeply'Toxic components of the crude oil spilled may have even penetrated as far as groundwater supplies, new study warns
17:41 GMT, 30 November 2012
The dispersant chemicals BP used in response to the Deepwater Horizon disaster may have made oil sink deeper and faster into the beaches of the U.S. Gulf Coast, scientists have claimed.
A new paper warns toxic components of light crude may even have penetrated as far as groundwater supplies because of the chemicals.
After the 2010 blowout at the Macondo Prospect, BP released about 2.6million gallons of dispersant chemicals to deal with the huge quantities of crude oil spilling into the Gulf of Mexico.
Disaster: The blowout at the Deepwater Horizon rig in 2010 spilled about 206million gallons of light crude oil into the Gulf of Mexico, which BP tried to clear up using chemical dispersants
Dispersing the oil had the short-term effect of making the catastrophe look less severe, but little was known about the long-term environmental effects of the chemicals used.
Now scientists have warned that they may have simply made toxic components of the crude more mobile, allowing them to further penetrate beach sediments and leak back into the water where they could harm marine life.
Researchers from Utrecht University in the Netherlands and Florida State University examined the effects of the Corexit 9500A, a chemical dispersant BP pumped into surface waters and at the wellhead in response to the spill.
In a study detailed in the open-access journal PLoS ONE, they used laboratory-column experiments to simulate the movement of dispersed and non-dispersed oil through seawater-saturated beach sand.
They found that using Corexit 9500A has the unexpected effect of allowing potentially harmful crude oil components called polycyclic aromatic hydrocarbons (PAHs) to penetrate deeper and faster into the sands.
Once there the lack of oxygen may slow the degradation of the PHAs, extending their lifespan.
Even worse, the researchers warned, using such dispersants in oil spills near to the shore could allow these chemicals to penetrate sands deeply enough to threaten groundwater supplies.
Experiment: Clean seawater, crude oil dispersed
by sonication, or crude oil dispersed by Corexit and sonication were
flushed through the sand columns by gravity. The effluent of the columns
was collected as a time series
The researchers say that the application of the dispersant chemicals changed the behaviour of the oil when it hit the gulf coast's beaches in three ways:
It transformed the oil into tiny particles that were better able to permeate through the sand;It coated these particles in such a way that they were less likely to stick to sand grains;And it coated the sand grains themselves, making them less able to hold on to the oil.
This meant that as waves from the gulf repeatedly flushed contaminated beaches, PAHs were pumped deeper and deeper into the sediment when dispersant was present.
It also meant that the flushing effect of the tides on an oil contaminated beach could allow the release of PHA's from the sand back into the water.
Once that has happened UV-light can increase their degradation, but it also potentially increases their toxicity by up to eight times with a range of disastrous effects on marine life.