Credit: Slug Signorino

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Did the oil spill in the Gulf of Mexico really cause any lasting environmental damage? Or did the environment just kind of take it in stride?

You know the old saying: Don’t cry over spilled oil—at least not if you’re getting billions in damages to make up for it. These things are bound to happen, right? A couple CEOs get fired, the president shakes his head disappointedly, and we’re a little short on Bayou shrimp for a year or so. But before long someone drops a bomb on someone else, or someone new turns up naked on the cover of something. Twenty-eight billion-plus in clean-up costs later and we can’t help but turn our eyes to more pressing matters.

In all honesty, though, you ask a fair question. Two hundred million gallons of crude oil gushed out into the Gulf of Mexico over the three months following the Deepwater Horizon explosion in April 2010—19 times the official volume figure for the Exxon Valdez spill of 1989—and then another two million gallons of chemical dispersants were pumped in to break up the slicks. President Obama called it a “potentially unprecedented environmental disaster.” Despite all this, the surface-level answer is that things are better than one might have feared: Humans, sea creatures, and BP alike have all seemingly recovered. The entire state of Louisiana wasn’t classified as a biohazard, and not all the dolphins died. But the consequences aren’t entirely dismissible, and the worst damage is often the hardest to quantify. It’s only been four and a half years, after all; some effects might not show up for decades.

Part of the reason things look so peachy is that the spill originated 50 miles offshore—oil didn’t penetrate much more than a few yards past the shoreline. What oil did manage to get that far was extensively weathered, meaning it had lost most of its volatile organic hydrocarbons, and with them a lot of capacity for damage. As a result, marine life closer to shore fared surprisingly well. Crab and shrimp were found to have three times as many deep lesions as before the spill, but fortunately they have an admirable reproductive instinct and their numbers rebounded to pre-spill levels very quickly. Fish were discovered with similar lesions, but these decreased by more than half after two years.

But, much like when the dog pees on your kid’s bed instead of yours, just because the damage isn’t front and center doesn’t mean it isn’t there. Promising population totals notwithstanding, there’s plenty of evidence to keep both the environmentalists and the fishing industry awake at night.

Various heavy metals contained in oil from the spill have been accumulating in the flesh of the gulf’s sperm whales ever since. Among these, nickel and chromium in particular are carcinogenic (some dispersant ingredients may be too), which could lead to mutations and resulting long-term impact on the ecosystem. Fish near the site have shown evidence of DNA damage, and studies suggest exposure to oil-spill hydrocarbons would likely cause heart defects in developing tuna, swordfish, and other large predator fish, limiting their ability to hunt for food. Something like 200,000 to 700,000 birds have died thus far following contact with oil; it’ll probably wind up being a million eventually. Dispersant chemicals were found in pelican eggs in Minnesota (where the birds migrate to) two years after the spill. And finally, the mammals: While only around 100 whale and dolphin carcasses were found in the months immediately following the spill, estimated historical carcass-to-death ratios suggest that 50 times as many may actually have died. Dolphins in the areas hit hardest with oil showed numerous health problems, with nearly half expected to die.

The impact on human mammals isn’t so clear either. Leaving aside the eleven oil-rig workers killed on the day of the explosion, a study of 117 people involved in the cleanup found changes in their blood chemistry and levels of liver enzymes; they also reported a variety of chronic conditions like headaches, rashes, and shortness of breath. Health surveys showed that alcohol and illegal drug use increased among residents in affected counties, with the most psychological stress on fishers and coastal dwellers. Overall, however, spill-specific results were difficult to distinguish from the lingering traumatic effects of hurricanes Katrina and Rita. It’s been a tough decade on the Gulf Coast.

If you’re still inclined to conclude that Obama’s a dirty liar (The environment’s fine! And these shrimp are terrific!), you should consider this: The 2010 spill was enormous, but only 8 percent of the total oil making its way into North American oceans each year comes from pipeline spills. The fact the environment recovered to the extent that it did is impressive, but this spill was just one of many, many factors contributing to to the ongoing damage of the marine habitat. Maybe in 20 years our waters will be full of three-eyed mutant fish, maybe not. We can predict with some confidence that however apocalyptic the future scenario, the Deepwater Horizon spill was probably a contributor.