That Deepwater Horizon spill… it’s still killing dolphins.

Nature has the grisly details about the 1,300 dolphin deaths that can be traced to that one incident:

The spike in dolphin deaths began shortly before the spill in April 2010, and scientists have struggled to understand whether the two events are related. A study published on 20 May in PLoS ONE finds that many of the dead animals had lung and adrenal-gland lesions that are consistent with exposure to petroleum compounds.

That led the study’s authors to conclude that the Deepwater Horizon spill probably drove the mass deaths.

In the latest study, researchers analysed lung and adrenal-gland tissue samples from 46 dolphins that were found dead in Louisiana, Mississippi and Alabama — areas that experienced significantly elevated levels of petroleum compounds. The team compared these animals with a reference group of 106 dolphins that stranded before the mass deaths began, or outside of the area where these strandings took place.

The dolphins that died in the footprint of the Deepwater Horizon oil spill were more likely to have lesions in their lungs and adrenal glands than animals from outside that area were, says Kathleen Colegrove, one of the study’s authors and a veterinary pathologist at the University of Illinois at Urbana–Champaign.

More than one in five dolphins from the mass-death group had bacterial pneumonia, and the disease caused or contributed significantly to the deaths of 70% of these animals. In contrast, just 2% of the animals in the reference group had pneumonia.

“What’s been really striking to me as a pathologist has been the severity of some of these pneumonias,” Colegrove says. “They’ve been some of the most severe pneumonias that myself or some of the other pathologists involved in this investigation have ever seen.”

Dolphins in the Deepwater Horizon footprint were also more likely to have a thin adrenal cortex, which can increase the risk of death and disease — especially in animals that are already fighting infection, exposed to cold temperatures or are pregnant. The condition was observed in a third of the animals from the mass-death group….