If you took 1,000 liters (264 gallons) of ocean water, how many pieces of plastic do you think you’d end up with: a hundred? A thousand? A hundred thousand?

According to a new study, the answer is 8.3 million. That’s 8,300 for every liter of water, or 31,439 per gallon.

That’s also a million times more than previous estimates.

A big tiny problem

The problem with plastic is that it never really goes away — well, it does go away, but it takes centuries or millennia. Instead, what plastic usually does is break down into smaller and smaller pieces, until you can’t really see it; but it’s still there.

Microplastics are pieces of plastic smaller than 5 millimeters. They come from a variety of sources, either from products that contain microplastics themselves (like some cosmetics or cleaning products) or from larger pieces of plastic that break down.

Plastic is everywhere, and it usually makes its way into the oceans. It doesn’t just stay in the water. It’s absorbed by creatures and accumulates higher up the food chain, even ending up inside humans.

It’s not exactly clear how microplastics are affecting wildlife and human health, but establishing just how much of it is around is a good step.

Biological oceanographer Jennifer Brandon had an unsettling idea: what if we’ve been counting microplastics wrong? She suspected that the current counting methods miss the smallest plastic pieces.

“For years we’ve been doing microplastics studies the same way (by) using a net to collect samples,” said Brandon in a press release. “But anything smaller than that net mesh has been escaping.” She suspected that existing papers are missing some of the plastics.

“I saw these published size ranges and thought, we are under-sampling this smaller range. There’s a big knowledge gap,” Brandon said.

So instead, Brandon and colleagues used a different method, gathering samples from both water and salps, gelatinous filter-feeding invertebrates that suck in water both to eat and propel themselves around the upper 2,000 meters (6,500 feet) of the ocean. Salps suck in and expel the water. They presumably also expel the microplastics, but it takes them a few hours to do so, so you’d be able to see if their last meal included any microplastics.

The researchers gathered 100 salps and sent them to the Scripps Oceanography, where co-authors Alexandra Freibott and Michael Landry searched for plastic in salp guts. They used a fluorescent microscope because conveniently, plastic lights up when exposed to multiple wavelengths of light — which means it’s easy to detect with this type of method. But the results were not so convenient.

Out of the 100 analyzed salps, 100 contained microplastics. There is good reason to believe that close to 100% of all the ocean’s salps are infested with microplastics. This was even surprising to the researchers.

“I definitely thought some of them would be clean because they have a relatively quick gut clearance time,” Brandon said. The time it takes a salp to consume and defecate is two to seven hours. As filter feeders, salps are almost always eating.

From land to sea

Surprisingly, the concentration of microplastic wasn’t higher around the great garbage patch in the ocean. Instead, there seemed to be more pieces in surface waters closest to the shore. The most likely cause for this is runoff pollution from the land.

Other than that, the plastic distribution seemed to be quite uniform, which is quite concerning. This suggests that the plastic is spread throughout entire ecosystems. Since most plastics are too strong to be broken by bacteria and digestive systems, they are simply passed along the food chain. Humans don’t eat salps, but other things do — and other things eat those other things… and after a few connections, you end up in the range of fish that humans do eat.

“No one eats salps but it’s not far away on the food chain from the things you do eat,” Brandon said.

Some microplastics can also be small enough to enter the human bloodstream. While the consequences of this ingestion are not fully understood, there are valid concerns about potential health impacts.

Microbeads are not a recent problem. We’ve recently started to properly acknowledge it, but according to the United Nations Environment Programme, plastic microbeads appeared when the firs plastics appeared, more than 50 years ago. As the world is producing more and more plastic, the number of microplastics continues to grow dramatically. Researchers from several countries are working to understand their distribution and impacts. Studies such as this one fill an important knowledge gap in this direction.

You can read the full study here.