WASHINGTON (AP) - More than a month after oil stopped spewing into the Gulf of Mexico, big questions remain about where it is.

Scientists who've just finished a cursory examination of the Gulf are disputing government claims that half the leaked oil is completely gone from the ecosystem.

They've been looking at plant plankton at depths of anywhere from 900 to 3300 feet, and have found considerable toxicity. That's worrisome because plankton is a vital part of the food chain of the Gulf.

And, there's concern for how fast oil trapped at super-low levels can dissipate, to say nothing of the immense amounts of natural gas that also belched from the well in its 3-month assault on the Gulf.