A coalition of environmental groups says it has discovered that large-scale shipments of low-quality heavy crude oil from Canada’s tar sands are being delivered by rail for processing by Southern California refineries.

The groups on Tuesday called for an investigation by air-quality officials to evaluate the effects on health, air quality, safety and the climate of processing the heavy Canadian crude, which requires intensive processing to remove higher levels of sulfur to meet U.S. standards.

The Natural Resources Defense Council and Communities for a Better Environment say they worry that refineries now processing the semi-solid form of oil have increased their noxious emissions and raised risks of accidental spills and accidents. The process of refining tar sands oil is more corrosive on refinery equipment and produces more greenhouse gases than liquid crude, environmentalists said.

“Tar sands crude is a whole new level of bad,” said Julia May, senior scientist at the Communities for a Better Environment, a nonprofit dedicated to preventing and reducing pollution in California’s low-income communities. “Bringing it into the Los Angeles area by rail has taken everyone by surprise.”

Of particular concern is the low-income community of Wilmington, a Los Angeles harbor town surrounded by five oil refineries and long decried by social justice groups as a “sacrifice zone” of commerce and toxic pollution. Three of the Wilmington refineries — Valero Energy Corp., Phillips 66 Co. and Tesoro Corp — recently announced plans to use rail cars to bring in more of the heavy Canadian crude.

Joe Gorder, president and chief executive of Valero Energy Corp., told shareholders recently that his company plans to import an additional 30,000 barrels a day of the Canadian crude to its Wilmington refinery. Deliveries of the heavy crude totaled about 29,000 barrels a day last year for the entire Los Angeles area, NRDC scientists said.

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