Deep underwater currents are creating large build-ups of microplastics in biologically rich areas on the sea floor.
Ian Kane at the University of Manchester in the UK and his colleagues analysed the effect of slow-moving currents on the accumulation of 鈥� fragments and fibres less than one millimetre in size.
Looking at currents in the Tyrrhenian Sea, off the western coast of Italy, the team found that in biodiversity hotspots at concentrations of up to 1.9 million pieces per square metre.
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Bottom currents, which generally occur at depths of between 600 and 900 metres, pick up and carry sediment from the sea floor, creating large accumulations elsewhere.
鈥淭hey can be kilometres in length and they can be hundreds of metres high,鈥� says Kane. 鈥淭hey鈥檙e ubiquitous in all of the world鈥檚 oceans.鈥�
The currents are beneficial to sea life, says Kane.聽鈥淥cean currents also transport nutrients and they transport oxygenated water, so they can often support quite diverse ecosystems on the sea floor.鈥�
But they appear to also be sweeping up plastic waste. The researchers collected samples from sediment deposits at 16 sites on the sea floor, at depths of up to one kilometre, and found that the locations of microplastic hotspots correspond with these biodiverse ecosystems.
Microplastics by themselves are relatively inert, says Kane, but can accumulate toxins such as heavy metals, which become more concentrated as they are ingested and moved up the food chain.
鈥淭hey could potentially go through many different organisms in the lifespan of a single microfibre or microplastic fragment,鈥� says Kane.
Nearly all the microplastics the team found were , either from clothing or industrial processes.
The research highlights the need for better filtration systems and wastewater treatment plants, says Kane. 鈥淭hat鈥檚 where most of this material is coming from.鈥�
Most of the plastic in the ocean is thought to end up in the deep sea, with estimated to account for only one per cent of all marine plastic.
Science
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