Earthworms like to eat some plastics, but side effects of their
digestion are unclear

Date:
April 6, 2022
Source:
American Chemical Society
Summary:
Earthworms are a welcome sight for gardeners and farmers because
the wriggling invertebrates recycle nutrients from soil, making
them more accessible to plants. As worms burrow, they consume
almost everything in their path, including microscopic plastic
pollution. Now, researchers have observed that earthworms actually
prefer soil with some types of microplastics but digest the polymers
differently, which the team suggests could impact the animals'
health and the ecosystem.



FULL STORY ========================================================================== Earthworms are a welcome sight for gardeners and farmers because the
wriggling invertebrates recycle nutrients from soil, making them more accessible to plants. As worms burrow, they consume almost everything
in their path, including microscopic plastic pollution. Now, researchers reporting in ACS' Environmental Science & Technology have observed that earthworms actually prefer soil with some types of microplastics but
digest the polymers differently, which the team suggests could impact
the animals' health and the ecosystem.


==========================================================================
Soil is becoming increasingly contaminated by fragments of plastic -
- especially microplastics less than 5 mm wide -- that have broken off
of larger plastic waste or have been directly released from products as
small particles. Previously, researchers have shown that earthworms will
ingest these synthetic particles, even breaking them apart into smaller
pieces. But during the digestion process, animals could potentially be
harmed by the microplastics themselves or by the toxic substances they
carry. Currently, companies are producing alternatives to petroleum-based plastics that are derived from plants, are biodegradable or both. Just
like traditional plastics, these "bioplastics" can also fragment into microscopic particles, but there is limited information on whether
earthworms will also ingest and decompose these materials. So, Lei Wang
and colleagues wanted to compare the willingness of earthworms to consume
soil laced with microscopic pieces of bioplastic and petroleum-derived
plastic, studying the in vitrodigestion and excretion of the particles.

By placing earthworms in chambers with different types of plastics in
certain locations in the soil, the researchers found that worms preferred
soils with bio-based polylactic acid (PLA) particles or petroleum-derived polyethylene terephthalate (PET) particles but actively avoided
some semi-synthetic plastics. When lactic acid and terephthalic acid, sour-smelling monomers that make up PLA and PET, respectively, were spiked
into soil, the worms were also attracted, suggesting that the animals were drawn in by the odors as potential cues for food. In another experiment,
the researchers put earthworms in soil mixed with either microscopic
PLA or PET particles. Analysis of the creatures' excretions showed that
their digestive systems broke down PLA into much smaller fragments than
was observed with PET plastics. The animals also excreted PLA much more
slowly. The researchers say the results show that earthworms can promote
the breakdown of bioplastics, such as PLA, in soil. They add that more
studies are needed to determine how the slow excretion of PLA fragments
affects the health of these animals and whether the worms are an option
to remove degradable plastics from the environment.

The authors acknowledge funding from a National Key Research and
Development Project of China, the National Natural Science Foundation of
China, the Tianjin Municipal Science and Technology Bureau, the Ministry
of Education (China) and the Tianjin Research Innovation Project for Postgraduate Students.


========================================================================== Story Source: Materials provided by American_Chemical_Society. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Lei Wang, Yawen Peng, Yali Xu, Junjie Zhang, Chunguang Liu,
Xuejiao Tang,
Yuan Lu, Hongwen Sun. Earthworms' Degradable Bioplastic
Diet of Polylactic Acid: Easy to Break Down and Slow to
Excrete. Environmental Science & Technology, 2022; DOI:
10.1021/acs.est.1c08066 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220406101636.htm

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