oil is compared with the toxicity of the crude oil that has been dispersed by using the dispersant. And as long as the toxicity is not increased when dispersant is used, then that dispersant is approved.
The reason I mentioned the tainting in particular is that it is a lower-level effect. The first effect that you-might look for, I agree, is a toxic effect resulting in a kill of fish populations. Even in the BRAER incident, where you are getting as high a concentration of oil as you are ever likely to get, the fin fish swam away from the dispersed oil. So therefore, there were no acute toxic effect to any moving organisms. That was also the case in the SEA EMPRESS incident. There were no acute effects to any organisms that could actually move away from the dispersed oil. The organisms that are more likely to be affected by the dispersed oil are those like the bivalves, which are anchored to the substatum. With them, there is more likely to be an effect of physical smothering, and the oil droplets, particularly for the filter feeders, clogging up their filtering mechanisms. There were some acute effects, particularly near the spill site. I mentioned those with regard to the SEA EMPRESS, again the same with the BRAER. Those are very localized within something like the first kilometer from where the oil was spilled in both those cases. Bivalves were affected, and there was actual mortality with the bivalves in that local area. But it was very localized, and as soon as the concentration is diluted to below about 10 parts per million, then there aren't those acute toxic effects. And that has been a threshold level that has been agreed upon in some of the workshops that have been held in North America recently. If the concentrations are not exceeding 10 ppm for more than 2 hours, then acute toxic effects are unlikely.
Coming back to the tainting issue, there is the possibility of tainting of the flesh, in terms of being able to taste the oil in the flesh, which makes the fish unmarketable, at much lower oil concentrations. But that's a commercial fisheries' issue rather than an environmental issue.
And the final point that you raised, on the plankton, in the area where the oil is first dispersed into the water column, if the concentrations are significantly above 10 parts per million, which does not happen often, and did not happen in the SEA EMPRESS incident, even after dispersant application, there is likely to be a toxic effect. And there will be some reduction in the plankton population. I think then, in terms of net envi-ronmental benefit, that effect has to be weighed against what might be a toxic effect if the oil hits the shoreline. There is very rapid recolonization of plankton in most open seas. I am not aware of, and Alan Mearns might want to comment in more detail about, any studies that have shown that dispersed oil in any concentration results in a significant impact on any open-sea plankton population.
Mearns： In the United States some years ago, we seemed to be approaching whether or not to use dispersants from the point of view that if you did not use dispersants you would not have any oil in the water. With most of the oils and fuels that we deal with, there will always be some amount of oil in the water. So, from a marine biological point of view, I think that the answer is not that we are putting oil into clean water, but we are putting oil into water that already has oil in it. And the question is : "How much is too much?" But to start with the assumption that there is no oil in the water is wrong.
The second thing is that we have learned a lot from these oil spills in the U.K., and in Canada to some extent, and in the United States about how fast tainted animals lose oil. It's what we call depuration. And there is a very fast process, perhaps a half-life of a week or 2 weeks at the most, for most fish or crustaceans that are contaminated to lose their oil. It's a very rapid process, once they get into clean water.
There is another point that I have been very interested in for a long time, and I think I have discussed this with Dr. Lunel and his colleagues to some extent. There was a very interesting study done in Canada 25 years ago, where a scientist sampled the plankton, copepods and small animals, and found they were alive during an oil spill, and they had 7,000 parts per million of Bunker-C oil in them. They were feeding on these fine dispersed particles of oil and using the oil as food. And they were alive and well and producing fecal pellets.
