Published: Nov 25, 2013 1:08 PM EST

CHICAGO (AP) - There's a new environmental concern in America's heartland.
    
Huge black piles of petroleum coke are accumulating along Midwest shipping channels, raising concerns about how it could affect public health.
    
Petroleum coke, or "petcoke" is a byproduct of oil refining that's burned as a fuel by some industries.
    
It appeared in Detroit and Chicago neighborhoods this year after nearby refineries expanded to handle a glut of heavy crude oil coming from Canada's oil sands region.
    
That oil has been trapped in the Midwest because of limited pipeline capacity to the South and West coasts.
    
Companies that handle petcoke say it's not hazardous.
    
But Detroit officials ordered the mountains of petcoke removed after a cloud of it blew across the Detroit River. Chicago officials are debating whether to regulate or ban it.

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