In 83 percent of cases, the perceived dangers of ocean trash were proven true. In most of the remaining cases, the working group found the studies too shoddy to draw conclusions from—they lacked a control group, for example, or used faulty statistics.
Strikingly, Rochman says, only one well-designed study failed to find the effect it was looking for, an investigation of mussels ingesting microscopic plastic bits. The plastic moved from the mussels’ stomachs to their bloodstreams, scientists found, and stayed there for weeks—but didn’t seem to stress out the shellfish.
While mussels may be fine eating trash, though, the analysis also gave a clearer picture of the many ways that ocean debris is bothersome.
Within the studies they looked at, most of the proven threats came from plastic debris, rather than other materials like metal or wood. Most of the dangers also involved larger pieces of debris—animals getting entangled in trash, for example, or eating it and piercing their guts.
But a lot of ocean debris is “microplastic,” or pieces smaller than five millimeters. These may be the beads from a facial scrub, fibers shed by synthetic clothing in the wash, or eroded remnants of larger debris. Compared to the number of studies investigating large-scale debris, Rochman’s group found little research on the effects of these tiny bits. “There are a lot of open questions still for microplastic,” Rochman says, though she notes that more papers on the subject have been published since 2013, the cutoff point for the group’s analysis.
There are also, she adds, a lot of open questions about the ways that ocean debris can lead to sea-creature death. Many studies have looked at how plastic affects an individual animal, or that animal’s tissues or cells, rather than whole populations. And in the lab, scientists often use higher concentrations of plastic than what’s really in the ocean. None of that tells us how many birds or fish or sea turtles could die from plastic pollution—or how deaths in one species could affect that animal’s predators, or the rest of the ecosystem.
“We need to be asking more ecologically relevant questions,” Rochman says. Usually, scientists don’t know how disasters like oil spills or nuclear meltdowns will affect the environment until after they’ve happened, she says. “We don’t ask the right questions early enough.” But if ecologists can understand how the slow-moving disaster of ocean garbage is affecting ecosystems, they might be able to prevent things from getting worse.
Asking the right questions can help policy makers, and the public, figure out where to focus their attention. The problems that look or sound most dramatic may not be the best places to start. For example, the name of the “Great Pacific Garbage Patch,” a collection of marine debris in the northern Pacific Ocean, might conjure up a vast, floating trash island. In reality, though, much of the debris is tiny or below the surface; a person could sail through the area without seeing any garbage at all. A Dutch group called The Ocean Cleanup is currently working on plans to put mechanical devices in the Pacific Garbage Patch and similar areas to suck up plastic. But a recent paper used simulations to show that strategically positioning the cleanup devices closer to shore would more effectively reduce pollution over the long term.
“I think cleaning up some of these misperceptions is really important,” Rochman says. Among scientists as well as in the media, she says, “A lot of the images about strandings and entanglement and all of that cause the perception that plastic debris is killing everything in the ocean.” Interrogating the existing scientific literature can help ecologists figure out which problems really need addressing, and which ones they’d be better off—like the mussels—absorbing and ignoring.