Investigators say the driver may have tried to take the ramp too fast, causing the rig to overturn.
"The sludge oil is used to clean up the bottom of tanks and it does possibly contain some sort of Benzene," said Officer T.L. Roberson with the Houston Police Department.
Environmental crews are at the scene as well.
Meanwhile, commuters can go to Irvington, U-turn and come back or instead, can take the Hirsch exit to Kelly to continue on the Loop.
Houston police says the big rig driver was not injured in the wreck.
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