BP oil spill: toxicity of the oil dispersants
Do you know the toxicity of the oil dispersants?
It was pointed out that BP used Gulf of Mexico as a test ground for the real toxcity of oil dispersants, which still remains very mysterious for most of people.
A dispersant (COREXIT® EC9500A) has been applied to limit the environmental damage. However the dispersant self could possibly bring environmental damage. The specifications of the COREXIT® EC9500A can be found here.
It seems the COREXIT® EC9500A is not a very safe product. Long contact of this chemical can cause irritation to humans. If it is ingested by humans, it can cause nausea and vomiting. The repeated exposer to the chemical through inhalation can cause irritation to the respiratory tracts. It is suspected that this chemical also can cause some long-term damages to the marine lives.
It is claimed that there are not many scientific studies conducted to investigate the effects of using COREXIT® EC9500A to clean the oil spill. But, I have managed to find several studies of COREXIT® EC9500A.
Singer et al. (1996) made a comparison of acute aquatic effects of the oil dispersant Corexit 9500 with those of other corexit series dispersants. The research paper points out that the purpose of Corexit 9500 is to to orient at the oil–water interface, lower the interfacial ension, and facilitate the formation of small (<100 mm) mixed oil–surfactant micelles. The surface active components of corexit 9500 can bring some potential damages to marine creatures’ membranes. The study did not find the significant differences of chemical between Corexit 9500 and Corexit 9527.
Lessard and DeMarco (2000) reviewed the pros and cons of oil spill dispersants. In this review, it is pointed that the use of oil spill dispersants started from 1960s. In 1970s, and 1980s, there is a resistance in using oil spill dispersants due to the environmental damage concern (Torrey Canyon spill accident). From 1960s, the low-toxicity dispersant has started to be developed, which increases the use of oil spill dispersants in controlling the oil spill. This review pointed out the advantages of using oil spill dispersants.
(1) The dispersants can be used in harsh weather conditions, where there are rough seas, strong winds and currents. Under such conditions, the use of mechanical containment and recovery may not be very possible.
(2) The use of oil spill dispersants in a large area is feasible by using airplanes.
(3) Oil spill dispersants can delay the formation of water-in-oil emulsions. It is also capable of breaking down these emulsions once they are formed.
(4) Oil spill dispersants can facilitate the biodegradation process by increasing the surface area of bacteria.
(5) Oil can become less sticky to the sediment, wildlife, shorelines, vessels and so on.
The review also showed that the toxicity of dispersants could not be a big concern in practice. This conclusion, which i believed still very rough, is based on the long-term study of national research council, 1989, which studied the toxicity of Corexit 9527 (not the current use of Corexit 9500A for BP oil spill). The study also demonstrated that the short-term exposer to the concentration level of milligram per litre would not bring irreversible damages to marine lives.
National research council, 1989 demonstrated that some typical offshore dispersant concentration levels are ranged between 0.2mg/L to 1.0mg/L. The real sea dispersant concentration levels could be about 0.0003mg/L. However, it also noted that the concentration level of 0.5 to 2.0 mg/L could possibly exist in the top of 2.0 meters sea water.
In the thesis of McIntosh S (2009), it was pointed out that different marine species have different response curve to the dispersed oil. Within 24 hours, gametes and free-swimming embryos are the species, which can be severely impaired. Over 24 hours, young embryos (< 1 day old) are fragile to the dispersed oil.
Most of studies use controlled laboratory conditions (far from real sea state) to study the toxicity of dispersants. To mimic the real sea conditions, Li et al. (2008) constructed a wave tank system to simulate the real sea state situations. This close-to-real controlled study suggested that the effectiveness of oil dispersants is directly related to the energy dissipation rates of waves. It then implies that the toxicity of dispersants is also linked to the sea surface conditions.
Based on the above studies, we can conclude that the use of Corexit 9500 can help to minimize the risks of environmental damages. Meanwhile, Corexit 9500 bring some negative effects on the marine lives. Such effects are different for different marine species, which live in different water zones. Some of them live in shallow water, but others live in the deep water. The extent of adverse impacts should be analyzed based on the specific marine species in the containment water. Sea turtles, crabs, and shrimps are all threatened species due to the use of Corexit 9500.
The BP oil spill does not occur on the surface of sea. The oil spill was about 5000 feet under the ocean surface. The Corexit 9500 is also used below the sea surface. This could bring a new challenge. It is because most of previous studies considered the use of oil dispersant on the surface of water. More scientific studies are needed to investigate the impacts of Corexit 9500 to marine lives, when it is used in the deep sea.