One of the most worrying papers I’ve read this year is by Rillig and colleagues, proposing that microplastics could pose a threat to plants. Sadly, it’s time to update that title as a new paper published in Plants, People, Planet shows that microplastics do pose a threat to plants.
Mark van Kleunen and colleagues examined Ethylene propylene diene monomer (EPDM), a microplastic used in artificial sports turfs. They measured its effect on the growth of Plantago lanceolata and on competition between seven grassland‐plant species.
Microplastics have come to the public eye as a danger to aquatic systems, but they get into other ecosystems too. “Much less attention has been paid to the potential effects of plastic pollution in terrestrial environments…,” said van Kleunen and colleagues in their article. “This is surprising, because the release of plastic in terrestrial ecosystems is likely to be higher than in the oceans. For example, for the European Union, Horton, Walton, Spurgeon, Lahive, and Svendsen calculated that 4–23 times more plastic is released and retained in terrestrial environments than in the oceans. So, there is a clear need to test the ecological consequences of plastic pollution in terrestrial ecosystems…”
To test the effect of EPDM on plants, van Kleunen and colleagues conducted two experiments. One was growing Plantago lanceolata in varying concentrations of EPDM. They then measured how the plants grew. “[A]t low concentrations, the effect of the EPDM granules on biomass production was actually slightly positive,” the authors said in their paper. “The same, however, was also the case when we used cork instead of EPDM granules. Possibly, the addition of EPDM and cork granules, which were overall larger than most sand and vermiculite particles, improved the drainage or aeration of the soil. At higher concentrations, however, the effect of the EPDM granules became strongly negative and at concentrations above 8% v/v almost all plants died.”
The next experiment was to examine how EPDM affected competition between seven European grassland species. “We grew each of the seven species as target plants without competition, and in competition with a plant of the same species (intraspecific competition) or a plant of one of the other six species (interspecific competition),” said van Kleunen and colleagues. “Competition, as expected, resulted in a reduced growth of the plants. The effect of competition, however, was weaker in the presence than in the absence of the tested granules. Probably, this reflects that the granules reduced the growth of both plants in a pot, and that due to their small sizes they interacted less intensively. Nevertheless, if the two plants are differently affected by the granulate, the competitive balance between them might change.”
The authors caution that this is one study, so it’s too early to draw general conclusions about the effects of microplastics. Sadly though, it seems their findings are consistent with the warning from Rillig and colleagues in New Phytologist earlier this year. If we study the effects of plastics, we might well find more serious problems to tackle.