DETROIT (WWJ/AP) – Tests by the Michigan Department of Environmental Quality have found that hulking black mounds along the banks of the Detroit River in southwest Detroit don’t pose a threat to human health.

The petroleum coke, or pet coke, mounds are a byproduct of oil refining used in energy production. The material has been brought by trucks from the nearby Marathon Petroleum Co. refinery. The pet coke is stored at a site off Jefferson Avenue in southwest Detroit, where it’s loaded onto freighters.

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The mounds drew attention starting earlier this year. Area residents, the Canadian government and U.S. lawmakers are among those concerned about potential pollution and health effects.

Findlay, Ohio-based Marathon Petroleum says the pet coke stored along the Detroit River is no longer owned by the company. Officials say it was sold to Wichita-based Koch Minerals LLC, who couldn’t be reached for comment.

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Andrew Hartz, district supervisor of the DEQ’s Water Resources Division in Warren, told The Detroit News that the pet coke will apparently continue to be produced “in large volumes for some time to come.”

“They are controlling storm water on the site — not allowing it to release from the piles into the river,” Hartz said. “And the only real issues we’ve seen from the dust perspective have come when the material is being loaded onto conveyor belts leading to the ships.”

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