WASHINGTON (AP) -- Federal regulators say a scientific analysis of dioxin exposure in the Midland-Saginaw area won't be much help as they plan the cleanup of dioxin pollution near a Dow Chemical Co. plant.

The Environmental Protection Agency said Thursday the University of Michigan study provided good information but failed to answer crucial questions. EPA said that limits its usefulness in designing the cleanup of a polluted 50-mile-long watershed near the Midland plant.

The 2006 study found that some residents of the two counties had elevated dioxin levels in their blood. But it also concluded that where they lived wasn't a significant factor in determining those dioxin levels.

The lead scientist, David Garabrandt, said regulators and Dow officials should use its findings as they plan the cleanup.