Oil spill clean-up agents threaten coral reefs

One of the main advantages of biofuels and bioproducts is their biodegradability. Especially in marine environments this is an important benefit (more here and here). A biofuel spill would not have the disastrous consequences seen when an oil tanker breaks and releases petroleum into the sea.

Oil-spill clean-up agents are more lethal to coral reefs than the oil they are supposed to clean-up

There is no easy fix to clean up sticky black crude oil once it has been released into the marine environment. What is more, researchers from the National Institute of Oceanography in Israel now report a major setback for efforts to protect endangered coral reefs from such spills: oil dispersants - the best tool for treating oil spills in tropical areas - are significantly more toxic to coral than the oil they are used to clean up. Their study, which urges caution in the use of these materials, has been released as an open access article in Environmental Science & Technology.

Called the 'rainforests of the sea', coral reefs are an endangered ecosystem and are disappearing at an alarming rate due to numerous threats, including over-fishing, global warming and pollution, particularly oil spills. Besides hosting a rich diversity of marine organisms, these habitats are also potential sources of life-saving medicines and food for humans. Scientists looking for better ways to protect this important habitat have recently focused on the environmental impact of oil dispersants, detergents used break down oil spills into smaller, less harmful droplets.

In the new report, Shai Shafir and colleagues evaluated the effects of both crude oil and six commercial oil dispersants under laboratory conditions on the growth and survival of two important species of reef corals. The dispersants and dispersed oil droplets were significantly more toxic to the coral than the crude oil itself, the scientists report. The dispersants caused significant harm, including rapid, widespread death and delay in growth rates, to the coral colonies tested even at doses recommended by the manufacturers, they add.

In this broader study, we employed a "nubbin assay" on more than 10 000 coral fragments to evaluate the short- and long-term impacts of dispersed oil fractions (DOFs) from six commercial dispersants, the dispersants and water-soluble-fractions (WSFs) of Egyptian crude oil, on two Indo Pacific branching coral species, Stylophora pistillata and Pocillopora damicornis. Survivorship and growth of nubbins were recorded for up to 50 days following a single, short (24 h) exposure to toxicants in various concentrations. Manufacturer-recommended dispersant concentrations proved to be highly toxic and resulted in mortality for all nubbins.

It is estimated that 40% of global crude oil transport is conducted offshore with much of the traffic, taking place in tropical, coral reef-rich areas. This heavy maritime traffic of crude oils and their products is prone to accidents, resulting in major or minor spillages. Although the number of major oil spills has decreased in the past decade it is still, by far, the most serious threat to the marine environment:
energy :: sustainability :: crude oil :: petroleum :: oil spills :: biodiesel :: biodegradable :: biofuels :: coral reefs ::

Of the three major ways for treating marine oil spills (chemicals, mechanical containment booms, skimmers and sorbents, biological-biodegrading microorganisms), chemicals, mainly oil dispersants, are probably the most commonly used, the scientists say.

Dispersants are chemicals that contain surfactants and/or solvent compounds that break down floating oil into small droplets within the water-column, which makes the spill less likely to reach shore. Dispersed oil is subjected to natural forces such as waves and currents that promote dissolution of oil droplets.

Use of dispersants for treating oil spills is governed by local and national regulations determining, for instance, distance from shore and depth at which treatment is allowed. However, since most oil-tanker accidents occur near the shore, it is essential to evaluate the impacts of oil dispersants on organisms that live on the seabed, including sea grass populations and coral reefs.

Given that manufacturer-recommended dispersant concentrations proved to be highly toxic and resulted in mortality for all nubbins and that they were significantly more toxic than crude oil, the scientists rule out the use of any oil dispersant in coral reefs and in their vicinity.

The authors therefor urge decision-making authorities to carefully consider these results when evaluating possible use of oil dispersants as a mitigation tool against oil pollution near coral reef areas.

Image: Oil-spill clean-up agents are a threat to coral reefs, researchers say. Courtesy: Shai Shafir, The Hebrew University of Jerusalem.

References:
Shai Shafir, Jaap Van Rijn, and Baruch Rinkevich, "Short and Long Term Toxicity of Crude Oil and Oil Dispersants to Two Representative Coral Species", Environ. Sci. Technol., 41 (15), 5571 -5574, 2007. 10.1021/es0704582 S0013-936X(07)00458-0, Web Release Date: June 26, 2007, scheduled print edition August 1, 2007.