Revealed: Caddis flies uses plastic waste from their surroundings to build shells but the new protective layer actually makes it EASIER for predators to attack the mysterious underwater insects

Caddis flies are small insects that live on riverbeds and pond bottoms Scientists found they built narrow shells for themselves with plastic waste The plastic shells were weaker than ones they'd otherwise build with sand

As microplastics continue to fill the world's oceans and rivers, one mysterious yet resourceful insect is using the pollutants to build shelters for itself.

A new study from the University of Koblenz-Landau in Germany has revealed how caddis flies use the growing volume of microplastics in their surroundings as a construction material.

Caddis flies are tiny insects that typically live in riverbeds, ponds or streams, and build artificial shells around their bodies by arranging sand particles in complex webs of silk that they spin.

Small water-dwelling insects called caddis flies have been observed building long artificial shells for themselves using microplastics collected from riverbeds

According to the researchers, caddis flies will readily substitute microplastic particles for sand granules to create these long protective shells, which they add to in segments as they mature.

While it may seem like a clever adaptation, the team discovered caddis fly structures made with microplastics are actually weaker than those made with sand particles.

These weaker shells are easier for predators to break through and fall apart more readily when shifts in water currents or large ripples sweep through the environment.

According to the team, this was likely due to the fact that the plastic particles are lighter and softer than sand particles, which makes them more susceptible to external manipulation.

Microplastics also expose the caddis flies to toxic chemicals as they draw fresh water in through their shells as part of their respiration process.  

Caddis flies typically build these shells with small but hard particles of sand and a sticky silk webbing that's much more stable than the shells made from microplastics

Caddis flies are an important part of river ecosystems, helping to keep riverbeds from overgrowing with grasses, while providing a food source for other animals, like bats, spiders, and frogs

'They are creating water flow inside the case so the water passes their gills,' the University of Koblenz-Landau's Sonja Ehlers told Wired.

'And so if there's plastic incorporated, then of course those leachates could also reach the gills maybe and do some harm.'

While caddis flies are small they're not insignificant. They play an important role in river ecosystems by feeding on plants and grasses on riverbeds, which keep them from becoming overgrown.

They're also important prey for a number of other animals, including bats, frogs, and spiders, who might be exposed to toxic plastic material after eating caddis flies.

The researchers believed the plastic shells in part because the micriplastic particles are lighter and more flexible than sand particles, which makes them easier to pull apart and stretch in water currents, tearing holes in the underlying silk that holds them together

Caddis flies continue to add to their shells in segments as they grow from larvae to mature insects, something which microplastics make easier to see with different colored plastic particles

Microplastics have become a growing environmental concern as more plastic waste ends up in the world's oceans and rivers each year.

A recent study found there are nearly 2 million pieces of microplastic debris every 10 square feet of ocean in the world.

Scientists also recently discovered microplastics in Antarctic sea ice for the first time ever, giving an indication of how far plastic waste from the western world travels after its thrown away.

WHAT FURTHER RESEARCH IS NEEDED TO ASSESS THE SPREAD AND IMPACT OF MICROPLASTICS?

The World Health Organisation's 2019 report 'Microplastics in Drinking Water' outlined numerous areas for future research that could shed light on how far spread the problem of microplastic pollution is, how it may impact human health and what can be done to stop these particles from entering our water supplies.

How widespread are microplastics?

The following research would clarify the occurrence of microplastics in drinking-water and freshwater sources:

More data are needed on the occurrence of microplastics in drinking-water to assess human exposure from drinking-water adequately.  Studies on occurrence of microplastics must use quality-assured methods to determine numbers, shapes, sizes, and composition of the particles found. They should identify whether the microplastics are coming from the freshwater environment or from the abstraction, treatment, distribution or bottling of drinking-water. Initially, this research should focus on drinking-water thought to be most at risk of particulate contamination.  Drinking-water studies would be usefully supplemented by better data on fresh water that enable the freshwater inputs to be quantified and the major sources identified. This may require the development of reliable methods to track origins and identify sources.  A set of standard methods is needed for sampling and analysing microplastics in drinking-water and fresh water.  There is a significant knowledge gap in the understanding of nanoplastics in the aquatic environment. A first step to address this gap is to develop standard methods for sampling and analysing nanoplastics. 

What are the health implications of microplastics?

Although water treatment can be effective in removing particles, there is limited data specific to microplastics. To support human health risk assessment and management options, the following data gaps related to water treatment need to be addressed: 

More research is needed to understand the fate of microplastics across different wastewater and drinking-water treatment processes (such as clarification processes and oxidation) under different operational circumstances, including optimal and sub-optimal operation and the influence of particle size, shape and chemical composition on removal efficacy.  There is a need to better understand particle composition pre- and post-water treatment, including in distribution systems. The role of microplastic breakdown and abrasion in water treatment systems, as well as the microplastic contribution from the processes themselves should be considered.  More knowledge is needed to understand the presence and removal of nanoplastic particles in water and wastewater treatment processes once standard methods for nanoplastics are available.  There is a need to better understand the relationships between turbidity (and particle counts) and microplastic concentrations throughout the treatment processes.  Research is needed to understand the significance of the potential return of microplastics to the environment from sludge and other treatment waste streams. 

To better understand microplastic-associated biofilms and their significance, the following research could be carried out:

Further studies could be conducted on the factors that influence the composition and potential specificity of microplastic-associated biofilms.  Studies could also consider the factors influencing biofilm formation on plastic surfaces, including microplastics, and how these factors vary for different plastic materials, and what organisms more commonly bind to plastic surfaces in freshwater systems.  Research could be carried out to better understand the capacity of microplastics to transport pathogenic bacteria longer distances downstream, the rate of degradation in freshwater systems and the relative abundance and transport capacity of microplastics compared with other particles. Research could consider the risk of horizontal transfer of antimicrobial resistance genes in plastisphere microorganisms compared to other biofilms, such as those found in WWTPs. 

Can water treatment stop microplastics entering our water supplies?

Although water treatment can be effective in removing particles, there is limited data specific to microplastics. To support human health risk assessment and management options, the following data gaps related to water treatment need to be addressed: 

More research is needed to understand the fate of microplastics across different wastewater and drinking-water treatment processes (such as clarification processes and oxidation) under different operational circumstances, including optimal and sub-optimal operation and the influence of particle size, shape and chemical composition on removal efficacy.  There is a need to better understand particle composition pre- and post-water treatment, including in distribution systems. The role of microplastic breakdown and abrasion in water treatment systems, as well as the microplastic contribution from the processes themselves should be considered. More knowledge is needed to understand the presence and removal of nanoplastic particles in water and wastewater treatment processes once standard methods for nanoplastics are available.  There is a need to better understand the relationships between turbidity (and particle counts) and microplastic concentrations throughout the treatment processes.  Research is needed to understand the significance of the potential return of microplastics to the environment from sludge and other treatment waste streams.

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