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Mosquitoes Are Passing Microplastics Up the Food Chain

These reviled insects are adding another charge to their rap sheet: ferrying harmful microplastics ingested from contaminated water

Researchers fed microplastics to mosquito larvae in the lab. (imv/iStock)
smithsonian.com

We don’t exactly need another reason to detest mosquitoes. But on Wednesday, scientists at the University of Reading reported that, in addition to a dizzying array of deadly diseases ranging from malaria to Zika fever, these infamous insects can now ferry yet another growing public health concern: environment-contaminating microplastics.

Plastics have infiltrated just about every last corner of the planet—and while this initially spelled good fortune for cheap, disposable packaging, these human-made synthetics, like many others, have imperiled wildlife.

Marine animals in particular have been waging a losing battle with plastic pollution, entangling themselves in six-pack rings and choking on grocery bags. But some of the most dangerous contaminants—microplastics—clock in at less than five millimeters in diameter, and are often invisible to the naked eye. And size matters: The majority of ocean plastics—over 90 percent—measure less than 10 millimeters in length, marine biologist Matthew Savoca explained to Laura Parker of National Geographic last year.

These tiny terrors can be created when larger bits of plastic debris break down after they’re discarded, or enter sewage directly in the form of tiny beads found in many cosmetic products. Rather than felling animals through strangulation or the blockage of an airway, microplastics do their dirty work when they’re swallowed—an almost inevitable fate when our oceans have been polluted to the point of resembling “plastic soup,” as Parker reported for National Geographic.

Apart from potentially chauffeuring harmful chemicals or pathogenic microbes straight into the mouths of hapless fish and birds, microplastics can also crowd out actual nutrition as they accumulate, undigested, in animal bodies. Even worse, because they’re so hardy, microplastics—and their toxic baggage—move easily up through the food chain in both marine and freshwater environments, eventually landing on our own dinner plates.

The ubiquity of microplastics means that any animal that spends part of its life cycle in water could be vulnerable to exposure—and this new research shows that mosquitoes are no exception. Most of these bloodthirsty buggers lay their eggs in stagnant water, only fleeing the nest as adults. And, because most microplastics aren’t exactly biodegradable, even if they’re only ingested early on, they have a good chance of sticking around through adulthood.

And that’s exactly what the researchers found when they fed microplastics to mosquito larvae in the lab. Even though the insects weaned off the microplastics as they developed, a fraction of the contaminants stayed in their systems, eventually hitching a ride as stowaways aboard winged adults—who, in their natural environment, can eventually fall prey to mosquito-munching birds, bats and other insects, Josh Gabbatiss at The Independent reports.

“This [study] is just a proof of concept, but we know those plastics are in the environment in very large numbers,” study author Amanda Callaghan explains to Gabbatiss. “There’s no doubt this is going to happen in the wild.”

If true, this creates two pretty serious problems: Not only are microplastics getting the chance to climb new food chains, but they’re also getting dispersed far from the waters they initially contaminated. What’s more, mosquitoes aren’t alone in their semi-aquatic lifestyle: according to Callaghan and study co-author Rana Al-Jaibachi in a piece for The Conversation, many winged insects have similar life cycles, making them candidate carriers of plastic pollution.

“Aquatic insects are in the microplastic frontline,” explains Matt Shardlow, chief executive of the conservation charity Buglife, in an interview with The Guardian. Accordingly, other work has already shown that mayfly and caddisfly larvae in Wales are also harboring microplastics.

“It’s totally depressing,” Callaghan says in her Guardian interview. “These plastics are going to be around forever.”

Considering that plastic production is still expected to climb by 40 percent in the next decade, The Guardian reports, so too will the presence of contaminants in our food. Unless humankind takes action—quick—we’ll be tasting our own cold, hard, shiny medicine for years to come.

About Katherine J. Wu
Katherine J. Wu

Katherine J. Wu is a Digital Editor at PBS NOVA and Story Collider producer. She holds a Ph.D. in Microbiology and Immunobiology from Harvard University. Previously, she served as a AAAS Mass Media Fellow at Smithsonian magazine.

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