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Scientists: Oil Droplets Speckle Gulf Floor, Evidence Seen That Oil Has Become Toxic To Critical Marine Life

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ST. PETERSBURG, Florida -- University of South Florida marine scientists conducting experiments in an area of the Gulf of Mexico where clouds of oil from the BP spill were found now have discovered what appears to be oil in sediments of a vital underwater canyon and observed evidence that the oil has become toxic to critical marine organisms.

In preliminary results, the scientists aboard the R/V Weatherbird II discovered that oil-droplets are distributed on the Gulf's marine sediments in the DeSoto Canyon. The canyon is a critical area that provides nutrient-rich waters that support the spawning grounds of commercially important fish species on the West Florida Shelf.

The preliminary findings may suggest that sub-surface oil is emerging onto the West Florida Shelf though the canyon, a geologic feature located east-northeast of the Deepwater Horizon well site. To date, this is the eastern-most location for the occurrence of sub-surface oils.

Meanwhile, laboratory tests conducted aboard the Weatherbird II on the effects of oil have found that phytoplankton – the microscopic plants which make up the basis of the Gulf's food web – and bacteria have been negatively impacted by surface and subsurface oil. These field-based results are consistent with shore-based laboratory studies that showed phytoplankton are more sensitive to chemical dispersants than the bacteria, which are more sensitive to oil.

The observations from the scientists are pending confirmation in further laboratory tests at USF's College of Marine Science. TheWeatherbird II carrying 14 researchers and six crew members returned to St. Petersburg Monday from a 10-day research venture.

The researchers found:

-Water and sediment samples from east of the Deepwater Horizon wellhead (stations DSH 8, DSH9, DSH10) and at the edge of the DeSoto Canyon (station PCB-03) on the outer continental shelf are emitting visible fluorescence when examined under UV light, resulting in signals that match BP's MC252 oil.

Excitation Emission Matrix Fluorescence Spectroscopy (EEMS) of these water samples also indicated the presence of oil-like hydrocarbons. The UV-induced fluorescence, which has been digitally photographed, resembles a dense constellation of microscopic blue stars on the sediment surface and in the filter pads.

Fluorescence continued after five hours of freezing, suggesting that the fluorescence was not caused by living organisms. Minerals or other non-oil materials may also fluoresce in this manner, requiring the samples undergo further testing through molecular organic geochemical and compound-specific isotope analyses. Those tests will allow scientists to verify whether the fluorescence was due to the presence of petroleum hydrocarbons and whether the hydrocarbons are associated with BP's oil.

-Biosensor assays indicate that marine organisms, phytoplankton and bacteria, express a strong toxic response in subsurface and surface waters that show positive indicators of petroleum hydrocarbons. Two toxicity tests were employed: the Microtox Assay (SDI) and the QwikLite 200 Biosensor System (Assure Controls, Inc.) Both assays detect a toxic response as suppression of bioluminescence induced by the sample.

For Gulf samples, the dinoflagellate (QwikLite) assay indicated that the subsurface samples (the DHS08 sample taken at 275 meters depth and the PCB03 sample taken at 50 meters depth) had the greatest toxic responses followed by samples from DHS08 at 215 meters depth, PCB03 at 35 meters depth, and DHS10 at 60 meters depth.

These samples have not yet been statistically verified, yet 39 percent of the samples tested showed some degree of toxicity. DCMU/fluorometry, an indicator of phytoplankton health, confirmed that phytoplankton photosynthesis was stressed at the same stations that were determined to be toxic.

The bacterial (Microtox) assay indicated that the samples of surface waters of DHS08, DHS09, and FT1 were toxic - or 3 of the 14 stations (21.4 percent) had positive results. These field-based results are consistent with shore-based laboratory studies that showed that the dinoflagellate assay was more sensitive to dispersant than the bacterial assay which was more sensitive to oil.

  • These results indicate that a further, coordinated, comprehensive study and survey is needed to determine how extensive the contamination.

The August 6-16 Weatherbird II research cruise was funded by USF's Research Foundation and led by chemical oceanographer David Hollander, biological oceanographers John Paul and Kendra Daly and geological oceanographer David Naar.

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