As if the damage to flooded homes in Louisiana's coastal counties were not enough, Hurricane Isaac left behind another cleanup problem: the hurricane's storm surge and wave action uncovered old deposits of spilled oil and tar from 2010's devastating BP oil release. After finding tar balls and oil mats on the beach, Louisiana officials closed several stretches of beach to the public, the New Orleans Times-Picayune reported ("La. officials close 12 miles of coastline after Isaac washes up tar balls, oil from BP spill hotspot," by Bob Marshall.

Laboratory testing of oil samples from the affected beaches revealed the oil's chemical fingerprint, confirming the material as BP spill oil: "good solid matches," according to Louisiana State University chemist Ed Overton, who tested the oil for the state of Louisiana. The New York Post has that Associated Press report ("Tests confirm oil found on Louisiana beaches came from 2010 BP spill," by Cain Burdeau). Overton said the quantities of oil were far less extreme than in the original spill, and the oil has weathered to a less harmful condition.

Still, even the weathered oil has the potential to do damage, the Times-Picayune pointed out: "While the most toxic parts of raw oil quickly dissipate, the tar mats, tar balls and viscous sludge that reappear after storms remain a threat to fish, wildlife and humans, state authorities said. They can contain polycyclic aromatic hydrocarbons, known carcinogens that can also disrupt endocrine systems in both humans and wildlife."

And Auburn University researcher Joel Hayworth told the Associated Press that this year's event is likely to occur again: "We're in year three and this seems to be the new normal for the Gulf Coast. For some unforeseeable time, this is going to be the new normal for the beach."