We have underestimated the amount of microplastic in the ocean, by a factor of 2.5 at least. Many of the smallest pieces are thin fibres, not hard chunks.
Millions of tonnes of plastic waste enter the ocean every year, mostly as tiny fragments, known as microplastic, which are invisible to the naked eye.
鈥淲hen we started looking for microplastic in the sea, people used traditional plankton nets,鈥� says Penelope Lindeque at Plymouth Marine Laboratory in the UK. These have holes about 333 micrometres across, so fragments smaller than that can slip through.
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To find out how many smaller fragments were present, Lindeque and her colleagues trawled the ocean surface with three kinds of net. One had the standard 333-micrometre holes, while the others had holes 500 and 100 micrometres wide. They repeated the study in two widely separated regions: the Gulf of Maine and the English Channel.
鈥淭he smaller the net you use, the more microplastic,鈥� says Lindeque. The nets with 100-micrometre holes collected 2.5 times more microplastic than the standard plankton nets.
Extrapolating from these findings, the team estimated how much microplastic would be caught by a net with 1-micrometre holes. The calculations suggested there are 3700 pieces in every cubic metre of seawater.
That is far more than thought. For instance, an influential 2015 study estimated that there are 15 trillion to 51 trillion particles of microplastic in the ocean. 鈥淭hey always admitted that that budget is very conservative,鈥� says Lindeque, because it was based on studies that used 333-micrometre nets. The real total could 鈥渆asily鈥� be 10 times more, she says.
The smaller microplastics are a different kind to the larger ones previously found. Most of them are short, thin fibres, often blue or black.
鈥淵ou can鈥檛 be absolutely sure where they鈥檙e coming from,鈥� says Lindeque. But likely possibilities include fishing rope, textiles and clothes like fleeces made from artificial fibres that are shed. 鈥淚t can go through the washing machines because it鈥檚 so small, and it doesn鈥檛 get trapped by waste treatment plants, so it goes straight out into rivers and the sea.鈥�
鈥淲e don鈥檛 know if it鈥檚 harmful to us,鈥� says Lindeque.
However, lab experiments indicate that the microplastic harms tiny marine animals called zooplankton, which are crucial links in the food chain. 鈥淲e know it impacts on their reproduction,鈥� says Lindeque. 鈥淭hey still produce eggs, but the eggs are less likely to be viable.鈥� Larger animals like fish and whales rely on zooplankton to survive.
Environmental Pollution
