Microplastics now spread even further by flying insects
Scientists have recently discovered that microplastics can be transferred by flying insects from polluted waters to other environments – and into the food chain.
In an experiment carried out at the University of Reading, microplastics were fed to mosquito larvae, which inhabit water. When the larvae then changed into flying adults, scientists discovered that the microplastics were still within their digestive systems. The tiny plastics pieces of plastic have been found in half of the mayfly and caddish fly larvae in rivers in Wales, but this is the first time they have been found in the animals' bodies after their transformation from larvae to adult.
Microplastics are defined as anything smaller than five millimetres, tiny pollutants which are found in marine, freshwater and terrestrial ecosystems. They can originate from much larger pieces of plastic which have been broken up over time; they can also be released into the environment as already microscopic plastic pieces, such as microbeads, which were commonly used in the beauty industry in the UK until a full ban came into force in January this year, and microfibres. Synthetic clothing can release up to 700,000 minute plastic fibres during a single wash.
The new research involved fluorescent microbeads, which were readily ingested by the larvae. Professor Amanda Callaghan, who led the project, explained: “Larvae are filter feeders that waft little combs towards their mouths, so they can’t actually distinguish between a bit of plastic and a bit of food. They eat algae which are more or less the same size as these microplastics.”
When larvae undergo metamorphosis to become pupae, the front part of their gut dissolves. During this experiment, scientists found that microplastics survive this transformation because they are stored in pupae’s lower digestive system and thus are carried through to adulthood.
Larger pieces of plastic have been a cause of concern for marine life for some time, with animals in danger of choking on or being trapped by the items, but scientists are now beginning to understand how smaller forms of aquatic life, such as plankton, mussels and fish, can consume large amounts of microplastics. 70 per cent of the fish within the River Thames have ingested plastic, causing long term damage, while research has shown that microplastic ingestion decreases energy reserves in marine worms.
The food chain at risk
Culex pipiens mosquitoes were used in the experiment at Reading University, which has further serious implications – this species inhabits a vast range of environments around the world. Callaghan told the Guardian that it is “highly likely” that other flying insects starting life as water larvae will eat and subsequently retain microplastics. “You could have a lot of plastic going up [into the food chain]. It’s totally depressing. These plastics are going to be around forever.”
With aquatic life already threatened by microplastics, this research reveals that a whole new range of wildlife is being jeopardized. “This is a new pathway to get plastics up in the air and expose animals that are not normally exposed,” Callaghan said. “We don’t know what the impact will be.” Being a source of food for a range of animals, flying insects containing plastic within their systems will then contaminate larger insects, seabirds and other terrestrial vertebrates.
So far, microplastics have been found in the oceans, in Arctic sea ice and even in the Swiss mountains – as well as in tap water across the globe. In 2016, Eunomia Research & Consulting released research estimating that 950,000 tonnes of microplastics enter the ocean every year, while one river near Manchester has recorded the worst microplastic pollution in the world.
Matt Shardlow, chief executive of the conservation charity Buglife, said: “Aquatic insects are in the microplastic front line. We emit billions of plastic fibres every year, many of which go straight into rivers, so there is an urgent need for more research into the role microplastics may be playing in observed declines in aquatic life.”
The shocking reality
Microplastics are now a global cause for concern. Seemingly ubiquitous within our immediate environments and wildlife, the threat to humans from these minute pieces of plastic can not be overlooked. “We all eat them, there’s no doubt about it,” Callaghan said. Eating seafood, from mussels to tuna, which has ingested plastic straight from the ocean could pass that plastic into the human body; microplastics have also been found in salt and beer.
With plastic production only expected to grow in response to increased demand, scientists are calling for further experiments to investigate the effects of plastic on the human body, which are as yet unknown.