31 January 2020
By Adam Vaughan
Hotspots of microplastics can significantly reduce the number of certain animals vital to the ecosystems at the bottom of lakes, ponds and canals.
We know our waterways are being contaminated by plastic particles, but we don’t know if this is harming the animals that live at the bottom of freshwater bodies of water, which are a crucial source of food for larger species.
Now, a study has found that exposing a family of worms called Naididae to a high concentration of microplastics roughly halved their number. Losing the Naididae worms matters, says study author Paula Redondo-Hasselerharm at Wageningen University and Research in the Netherlands.
“The worms have an important role in the ecosystem: they incorporate the organic matter, they participate in the nutrient cycling of the system,” she says.
Redondo-Hasselerharm and her colleagues set up an experiment that mimicked plastic pollution in the Rhine river. They set up trays containing worms in a layer of sediment beneath fresh water in which between 0 and 5 per cent of the weight of sediment contained microplastics.
After three months, there was no effect on the worms in the sediment, but after 15 months the worms in sediment containing the highest concentrations of plastics had experienced “significant negative effects” on the abundance of different species of worms, the authors concluded.
Exactly how the microplastics harm the worms isn’t clear. Redondo-Hasselerharm says it is possible they ingest the microplastic and it remains within them, reducing their ability to eat and grow, and potentially killing them.
At lower concentrations of plastic – between 0.005 and 0.05 per cent – didn’t have a negative impact on the worms, and these are the levels that are more similar to the Rhine. But the apparently harmful level of 5 per cent microplastics may be found elsewhere in some plastic pollution hotspots, says Redondo-Hasselerharm, who believes they may be found more often in fresh water in the future.
Our knowledge about the hazard posed by microplastics is based on studies of short-term exposure, says Alice Horton at the UK National Oceanography Centre in Southampton, whereas organisms are more likely to be exposed to plastics in the long-term.
“This study gives the first evidence that long-term exposure can lead to different and more severe ecosystem effects than the short-term exposures usually studied,” she says. She echoes Redondo-Hasselerharm’s concerns that given our continued use of plastics, microplastic concentrations in the environment are likely to increase.
Hotspots of microplastics can significantly reduce the number of minuscule worms vital to the ecosystems at the bottom of lakes, ponds and canals, researchers have found.
Journal reference: Science Advances, DOI: eaay4054
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