A few facts about mosquitos: Only the females bite (unlike the males, they need the protein in blood to produce eggs) and they spend the first three stages of their life in water. New research has now added another unpleasant fact to this list – they can carry microplastics in their gut and kidneys from cradle to grave.
Microplastics are now a well-known menace, present in our water supply in vast quantities. The most recent estimate puts the total number of microplastic particles in the ocean at five trillion, a number so vast it’s hardly helpful in visualising the true scale. They reach the water in a number of ways – falling from our clothes in the wash, degrading from larger plastic items or washed down the drain in the form of cosmetic microbeads. Once in lakes, rivers and oceans they are consumed by marine animals and passed through the ecosystem as predator consumes prey.
Researchers from Reading University have now discovered another way that microplastics could be moving from water to land, with mosquitos being the first example of the phenomenon. Like many flying insects, female mosquitos lay their eggs in water. The young remain submerged as larvae (or ‘wrigglers’) and then as pupae (‘tumblers’), only leaving the water when fully-formed as flying adults. By feeding microplastic beads to mosquito larvae in a laboratory the team was able to show that they not only ate the plastic but that some of the particles stayed in their systems as they transformed into pupae and then flying insects. Though the quantity of plastic did decrease at each stage of growth, it did not disappear entirely.
Amanda Callaghan, lead author of the study, finds this new route to the skies alarming – ‘despair’ is the word she uses. ‘The bit that was most surprising was plastics going through metamorphosis and escaping their original form into the air,’ she says. ‘I find that really quite worrying. It means that there is this whole new route of microplastics getting into the environment – as if we need another one – because we know there are loads of lakes that are really heavily contaminated with microplastics that will be full of insects such as mosquitos that have this kind of lifecycle.’
Although Callaghan and her team haven’t tested insects living in the wild, she is confident that the results would be the same, particularly around lakes already proven to contain high levels of microplastics, such as Lake Garda in Italy and lakes in the US and Canada.
The key question is whether this is really a problem – are microplastics harmful to animal and human life? The answer is as yet unclear. In the course of her experiments, Callaghan was surprised to note that the microplastics didn’t appear to have any effect on the mosquitos tested, or on water fleas fed the same artificial diet. But she cautions against reading too much into this. ‘The fact that you can’t measure an impact in the laboratory doesn’t mean there isn’t an impact out there. I think it’s going to take decades before we really know what the impact of microplastics is.’ She also says that further research done by the team, as yet unpublished, shows a significant drop in the number of animals present in ponds that have been contaminated with microplastics.
Other studies are also emerging that demonstrate a negative impact on marine life. In one piece of research at the University of Exeter, marine lugworms were found to eat less and suffer low energy when living near ocean sediments heavily contaminated with microplastics. Another paper, from researchers at Plymouth University, showed that ingesting microplastics can also reduce the health of lugworms by delivering harmful chemicals to them.
This side-effect of microplastics is something that Callaghan is also keen to point out. ‘Quite often chemicals bind onto them and therefore they expose the animal to the chemical through eating the plastic, so it’s a kind of secondary poison,’ she says. It’s another reason why Callaghan’s lab-conditions, in which the microbeads fed to the larvae were in pristine condition, may not reflect the real dangers of plastic in the wild.
Then there’s the issue of nanoplastics, particles even smaller than microplastics (a common definition puts them at less than 0.001mm). Callaghan says that studies into these microscopic specks has shown that they can cross tissue boundaries: ‘They go through the gut into tissue and those are worrying because who knows what they’re going to be doing if they’re getting into tissues and cells.’
The unknowns are even greater when considering human health. It seems inevitable that microplastics will make their way to the top of the food chain but not what the impact will be. Scientists presenting a study on 23 October at United European Gastroenterology Week in Vienna revealed for the first time that they had found microplastics in the faeces of eight people from eight different parts of Europe and Asia. It’s no longer a question of whether they are there, but rather what they might do.
For Callaghan this is where the despair sets in. She’s adamant that lack of evidence shouldn’t lead to delay but is concerned about slow progress. ‘Everyone’s becoming much more aware but it’s got to translate into some action,’ she says. ‘Waiting to see what the impact will be down the line isn’t good enough.’
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