Where there's a will, there's a clay: Effects of clay on the Deepwater Horizon oil spill

The 2010 Deepwater Horizon oil spill is considered to be the largest oil spill recorded in US history. Approximately 4.9 million barrels of oil spilled into the Gulf of Mexico, leading to many reports of extensive damage to the surrounding marine organisms.

Oil spills have been a global issue for many years. Though the incidence of oil spills is decreasing due to better technology and different shipping routes, it is still having a damaging effect on the ecosystems that it comes into contact with. However, there are many marine bacteria, such as Alcanivorax and Cycloclasticus that can degrade oil via aerobic pathways. These obligate hydrocarbonoclastic bacteria (OHCB) are known as r-strategists; they are low in abundance in the environment until oil is available, causing them to rapidly multiply. These bacteria break down hydrocarbons in oil, thereby leading to its degradation.

Clay has been suggested to be a good way of increasing bacterial hydrocarbon degradation in oil samples. A study by Warr et al (2016) took two types of Deepwater Horizon oil samples: a fresh source oil taken from the oil rig and a weathered oil taken from the surface waters near the rupture. The compositions of these was determined using gas chromatography/mass spectrometry analyses, and have alkanes/PAH ratios of 9.4:1 and 29.8:1 respectively. It was found that the fresh source oil was not contaminated with any hydrocarbon degrading bacteria, so this samples was considered to be sterile. Two sets of batch experiments were prepared, one for the fresh source oil and one for the weathered oil. A batch containing only Galveston Water was included as a control. Three types of clay (Ca-bentonite, Fuller’s Earth and Kaolin) were used in the experiment and added individually to one experiment in each batch, along with the oil and Galveston Water. For each type of clay, fertilized clay flakes and natural clay flakes were tested. The rate of O₂ depletion in each of the tests was also measured.

The results showed that the lowest bacterial O₂ uptake occurred in the Galveston Water sample. All weathered oil samples showed significantly faster rates of O₂ depletion than fresh source oil samples, and the addition of Fuller’s Earth in both the fertilized and natural flake states showed significant enhancement of the rate of O₂ depletion compared to the control. Addition of the three types of natural clay flakes in fresh source oil samples only showed minor differences in hydrocarbon concentrations compared to the control without clay. However, the fertilized clay flakes showed significantly lower alkane concentrations than natural clay flakes in fresh source oil. The weathered oil samples had significantly lower alkane and PAH concentrations compared to the fresh source oil samples.

This study showed that fertilized clay treatments, especially Ca-bentonite and Fuller’s Earth, significantly enhance the biodegradation of both alkanes and PAH’s, but the authors suggest that this type of treatment is unlikely to help get rid of the toxicity caused by these oil spills. However, the fertilizer may have an impact on the marine organisms and the environment, which may be an area for future study if this method is to be used. I think that this was a good study, and was very useful in showing how oil spills could be dealt with, which could possibly lead to people using the clay approach in future oil spills and is a good basis for further research.

Reviewed paper: Warr, Laurence. N., Friese, Andre., Schwarz, Florian., Schauer, Frieder., Portier, Ralph. J., Basirico, Laura. M., and Olson, Gregory. M. (2016). Experimental study of clay-hydrocarbon interactions relevant to the biodegradation of the Deepwater Horizon oil from the Gulf of Mexico. Chemosphere. 162: 208-221. http://www.sciencedirect.com/science/article/pii/S0045653516309742