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A beachgoer holds a solidified piece of oil, or "tarball," which washed up on Dauphin Island, Alabama (map), in a photo taken on Saturday.
Tar balls found on the island are believed to be from the massive Gulf of Mexico oil spill, according to "comparison of the major biomarker indices" carried out by Louisiana State University for the National Oceanic and Atmospheric Administration. The oil leaks began when the BP-leased Deepwater Horizon oil rig exploded and sank last month.
Tarballs are common byproducts of oil spills, said Ronald Kendall, an environmental toxicologist at Texas Tech University. The sticky masses can form when ocean waves concentrate surface oil slicks into clumps, which then wash ashore.
The tar balls represent a risk to wildlife, Kendall added: They're "not as toxic or as big a problem as a sheen of oil that gets on feathers or fur, but they can still be toxic if swallowed." (See pictures of ten animals at risk due to the Gulf oil spill.)