And here’s yet another clue to the question of what happened to all that oil spilled into the Gulf of Mexico from BP’s blown well.

A Canadian toxicologist reports that dispersants did break up the oil and make it less visible—but in doing so, the oil was allowed to contaminate a volume of water up to 1,000 times greater than if the oil was left alone. As a result, the oil, along with the dispersant, was made much more readily available to living organisms, including micro-organisms and wiildlife.

On the plus side, the dispersed oil also became more readily available for hungry bacteria that devoured much of it, said Peter Hodson, an aquatic toxicologist from Queen’s University in Ontario. However, he said, as reported by nature.com:

Until it is degraded by such bacteria, the dispersed oil becomes mixed into the water rather than sitting on top of it. This means that its toxic constituents, most notably polycyclic aromatic hydrocarbons (PAHs), are likely to have a greater effect on marine wildlife.

Hodson’s research suggests that fish embryos, still in their eggs, are extremely sensitive to dispersed oil. "Exposures as brief as an hour can have a negative effect on embryonic fish," he says. That, combined with the fact that for any some species, large numbers of fish can spawn at about the same time of year, means that an entire hatch could be decimated by a plume of contaminated water.

As it turns out, the endangered Atlantic bluefin tuna spawn in the precise location of the spill and at the same time of year that the spill occurred (starting in April and continuing three months). Satellite surveys indicate that much of this year’s tuna spawn may have perished in the oil.

Hodson’s report, made public this week at a meeting of the Society of Environmental Toxicology and Chemistry in Portland, Oregon, was accompanied by statements from Ronald Atlas, a microbiologist at the University of Louisville, Kentucky, who has studied the aftermath of the 1989 Exxon Valdez spill in Alaska and says the toxic components of oil persist much longer than other components.

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