Science and Technology Daily Beijing, December 5 (reporter Hu Dingkun) swimming in the sea, choking water is inevitable. But according to Jennifer Brandon, a biological oceanographer at the Scripps Institution of Oceanography at the University of California, San Diego, who recently published a paper in Limnology and Oceanography Letters, you're not just choking in salty water, you're also choking in more than 400 microplastics.

The US National Oceanic and Atmospheric Administration (NOAA) defines microplastics as pieces of plastic less than 5 millimeters in diameter. Previous studies have suggested there could be anywhere from a few to hundreds of microplastic particles per cubic meter of seawater. However, the traditional way of measuring them is to filter seawater through a net, which can only find small plastic particles that are large enough.

Of more than 11,000 experiments conducted between 1971 and 2013, 90 percent used the same type of net, which can only trap plastic chunks larger than 333 microns (a third of a millimeter) in diameter, according to statistics. As Brendan says: "We've been using the same method for years, collecting samples with nets to study microplastics. But anything smaller than the mesh has escaped."

So Branden targeted even smaller microplastics with diameters between 5 and 333 micrometers. She filtered seawater with a polycarbonate filter with a diameter of just five microns. She also used a special fluorescent microscope to look for microplastics. She found 8.3 million microplastics per cubic metre of seawater, tens of thousands or even millions of times more than previously measured.

And, as she explains in the paper, "The particles in question were excluded, and our estimates are conservative and likely underestimate the total amount of microplastics."

The average adult takes a sip of water of about 50 milliliters. By Brandon's count, there are more than 400 microplastic particles in a single mouthful of seawater.

More significantly, Brandon also studied the ingestion of microplastics by small Marine plankton called salps. She examined 100 water samples collected in 2009, 2013, 2014, 2015 and 2017. She found microplastics in all types of salps, in all areas and at all stages of their lives.

Salps sit at the bottom of the Marine food chain, feeding on the smallest organisms in the ocean, such as nanoscale plants and microscopic zooplankton. The plastic in its body can travel up the food chain to the creatures that feed on it, such as sea turtles, grouper, king crabs, etc., and may eventually enter the human body. "Nobody eats sea salps, but it's not that far up the food chain from what you eat." Mr Brandon said.

< p> Editor's Circle < p> The oceans produce half of the Earth's oxygen, and to destroy the oceans is to destroy ourselves. But since the 1950s, human demand has led to an exponential increase in plastic production, which today has caused a large amount of plastic into the ocean, where the bulk will break down into particles. And those species at the bottom of the ocean food chain act as carriers, "responsible" for transporting the microplastic layers. Eventually, the particulate pollution spread far deeper and wider into deep-sea waters, sediments and animal communities than expected. If no action is taken, there will be more plastic than fish in the ocean by 2050; And even if we start now, the fight against plastic pollution in our oceans will be the "fight of the century," and we need everyone, every day, to get ready.

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