Feature

Let Seeping Oil Lie

Cleaning up an oil spill may produce more environmental damage than leaving such spills alone.

By Michael S. Foster

Large oil spills are usually accompanied by reports of widespread contamination, deaths of organisms, and predictions that the affected areas will become "biological deserts".

This perception of environmental damage, combined with real or imagined fears of economic impacts on fishing and tourism, often results in a massive effort to remove the spilled oil from the shore as completely and quickly as possible.

However, accumulating evidence from oil spills such as the Amoco Cadiz off France in 1978 and the Exxon Valdez in Alaska in 1989 suggests that cleanup can cause more environmental damage and result in longer recovery times than if the oil were left to degrade naturally.

Crude oil spilled on the shore is aesthetically offensive, disrupts normal uses of the polluted areas, and damages organisms and habitats. Public and scientific concern about these effects greatly increased with the widely publicised Torrey Canyon tanker spill in 1967. Although much of the damage caused during the Torrey Canyon spill was from the use of toxic dispersants, the belief remains that oil itself is extremely harmful.

In contrast to this belief, accumulating scientific case histories of oil spills have suggested that crude oil does not cause the severe damage to organisms or habitats that is often suggested in the popular media.

This is especially true on waveexposed shores, where mixing enhances natural cleansing. The scientific evidence indicates that the environmental effects of crude oil are generally short lived, and that shores that are not cleaned usually recover in one to three years after a spill.

There are exceptions -- sea otters and birds usually die if oiled, and habitats such as wave-protected estuaries and bays, tropical reefs and mangrove forests can be very adversely affected by crude oil.

However, even in these cases massive cleaning efforts do little to improve survival of oiled animals, and may increase the damage to habitats, not reduce it. The amount of damage to organisms living on or near shore is reduced when there is sufficient time (a few hours to a few days) for the more toxic, low molecular weight fractions of crude oil to evaporate before the oil reaches shore.

Mechanical Cleanup Damaging

Because dispersants used during the Torrey Canyon spill were so damaging, a great deal of effort has gone into developing mechanical techniques for removing oil from shores.

These techniques are commonly evaluated solely on their ability to remove oil, and rarely are the effects on organisms examined. This may be because of the belief that stranded oil causes more environmental harm than any possible mechanical cleanup.

Dispersants with very low toxicity have been developed since 1967, but their use is still under question, perhaps because of prior experience or simply because their use involves releasing additional chemicals into the sea. Tests have shown that modern dispersants are not very effective in dispersing oil once it has reached shore.

There have been claims of successful cleanup using bacteria that decompose oil. These techniques, called bioremediation, involve stimulating the growth of bacteria with fertilisers, or releasing bacteria that decompose oil. We have yet to see good evidence that bioremediation actually works this way on shores without damaging associated organisms.

The Exxon Valdez oil spill involved the first large-scale use of intensive mechanical cleanup. There was some evidence from prior oil spills that mechanical cleanup, such as the use of high pressure and hot water on rocky shores, or the mechanical removal of oiled marsh vegetation from estuaries, can cause more damage and result in longer recovery times than if such methods were not used.

Unfortunately, this information was largely ignored in the politically-charged crisis atmosphere of the spill, and a massive, multi-billion dollar effort was made to try to remove the oil from all contaminated shores.

Studies of the effects of this effort have been little publicised because numerous lawsuits between Exxon, the Federal Government, the State of Alaska, environmental groups, and native peoples placed severe constraints on the discussion and publication of results.

Most of the litigation is now over, and the evidence that is slowly emerging suggests that this massive cleanup effort on rocky shores may have been a greater environmental disaster than that caused by the oil.

A colleague, Andrew DeVogelaere, and I have been examining the effects of the use of several types of cleanup, including the widespread use of high pressure/hot water, on the rocky intertidal zone in one bay in Prince William Sound.

The shore in this bay and much of the rest of the sound is dominated by Fucus, an intertidal seaweed or rockweed common on many temperate shores of the world. Numerous periwinkle snails, limpets, and barnacles are associated with rockweed. It is habitat for foraging birds, and some marine fish such as herring lay their eggs on it.

We are comparing areas that were neither oiled nor cleaned; areas that were oiled but lightly cleaned, leaving behind a distinct oil band on the upper shore; and areas that were oiled and intensely cleaned with high pressure/hot water, with no oil band left.

Shores Scoured
To Death

The results show that intense cleaning removed nearly all large organisms from the rocks, leaving behind only a few dead plants. Moreover, while the species present and their abundances were similar between unoiled/not cleaned and oiled/lightly cleaned areas a year after the spill, the high intertidal zone of areas that had been intensely cleaned was still very different two years after the spill.

Rockweed on intensely cleaned upper shores has not recolonised well, only one of the many snail species is abundant, and barnacles commonly dominate the substratum. Fucus recovery is delayed in intensely cleaned areas partly because nearly all living, adult plants were removed during the cleanup. In Fucus populations, even a very few adults can enhance recovery by serving as sources of local recruits and providing favorable microhabitats for recruitment and growth.

We also marked patches of tar that were not removed by cleanup, and have found that most are removed naturally after one to three years. Another research group working at a variety of sites in the Sound has found similar effects.

These results indicate that if damage to and recovery of the environment is a primary concern during the response to an oil spill, then only manual techniques should be used during cleanup. These include the use of absorbent materials that can be easily removed from the environment, or vacuum pumping of accumulated oil from pools and skimming the water at high tide.

These methods should only be used if it is possible to minimise associated human disturbances, including those resulting from the disposal of oil and oiled debris on land.

Instead of massive attention to shores, responses should be directed at removing or dispersing oil at sea, and preventing it from stranding on shores, especially low energy shores such as bays and estuaries. The environmental effects of removing or dispersing oil offshore are minimal.

Although it has not yet been put into practice for large oil spills, perhaps the most important lesson is that decisions concerning the response to a spill should, as much as possible, be made before a spill occurs. It is difficult to rationally consider response alternatives or to educate during a crisis.

The best way to avoid shore damage is to skim, disperse, burn or otherwise prevent the oil from reaching shore. It is also necessary to plan for the protection of bays and estuaries.

Given that winds and currents can quickly spread oil on the sea, prior planning is the only way to ensure a rapid, environmentally sound response that minimises the amount of oil reaching shore. Experience has repeatedly shown that such a response is very unlikely if government agencies and the concerned public must agree to a response after a spill occurs.

Michael Foster is a professor of Marine Science at Moss Landing Marine Laboratories in California, and was a visiting Erskine Fellow at the University of Canterbury.