Insect larvae may contribute to microplastic pollution

For the study, the researchers presented larvae with pieces of plastic film cut from a commercially available biodegradable plastic bag, alongside pieces of oak leaf. Credit: Katey Valentine, University of York

Common insect larvae could inadvertently contribute to microplastic pollution in our rivers and waterways by chewing up litter, a new study published in Environmental Toxicology and Chemistry has found.

Researchers from the University of York looked at how the larvae of Caddisflies interact with plastic rubbish. Caddisflies are common insects inhabiting freshwater environments worldwide, such as rivers, lakes and ponds.

They found that the larvae can bite plastic into smaller pieces. The larvae then use to build the protective casing they live in until they are ready to transform into adult flies.

The researchers observed them choosing to gnaw through the plastic film instead of natural building materials. The larvae can generate hundreds of microplastic particles in a matter of days.

What are microplastics?

Microplastics are tiny plastic fragments often formed from the breakdown of larger plastic litter. Scientists have found microplastics everywhere they have looked, including in Antarctic ice, deep oceans, shellfish, drinking water, rain, and drifting in the air we breathe.

Scientists don’t know if these particles are dangerous, but the risks are considered high.

Lead author of the study, PhD student Katey Valentine from the Department of Environment and Geography at the University of York, said, “Given the increasing concern for the effects of plastic pollution on our environment, we wanted to understand whether caddisfly larvae would interact with items of plastic litter which commonly pollute the environment, and determine what the consequences of these interactions might be.

“The active use of plastic litter by freshwater animals could contribute to the formation of microplastics within these habitats. Further work is needed to determine how these animals could be utilising plastic litter. We also need to know how they create microplastics globally throughout natural freshwater environments. Further studies need to occur on whether other common freshwater species exhibit similar behaviour.”

Caddisfly larvae casings

Caddisfly larvae usually use natural materials such as sand, gravel and plant debris to build protective casings, weaving pieces together using self-produced silk.

The researchers presented larvae with plastic film cut from a commercially available biodegradable plastic bag. At the same time, the larvae received pieces of oak leaf. Although larvae generally tended to use more oak leaf material, many larvae used pieces of plastic to build their new case while leaving suitable pieces of leaf material untouched.

The plastic film used for the experiment was made from a bio-based polyester traditionally marketed as biodegradable. This marketing has increased its use in food packaging and agricultural mulching films as an “eco-friendly” alternative.

The degradation of this plastic is reported to be extremely slow in aquatic environments. It is therefore thought to pose a similar pollution risk as conventional plastics.

Professor Alistair Boxall, said, “Our work also shows how these organisms can exploit plastics to construct their homes. This could make the larvae more prone to predation and increase exposure to additives that will slowly leach from the plastic.”

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