Mosquitoes could carry plastic particles in the food chain

Mosquito larvae eat microscopic pieces of plastic that can remain in their bodies as they metamorphose into adulthood, researchers have shown for the first time. Amanda Callaghan, Associate Professor of Zoology, explains that they and similar insects could spread plastic particles that contaminate aquatic ecosystems – where many insects spend their childhood – to land predators such as birds or spiders. at the University of Reading in England.

Callaghan's study, detailed this week in Letters of biologyis the latest in a series of research studies on the potential impacts of tiny pieces of plastic that have accumulated in the environment from the sea floor to agricultural land, as more and more large plastic waste is decomposing. These microplastics are small enough to be ingested by smaller creatures, increasing the potential for them to accumulate in the food chain. It remains to be seen if this occurs in the wild – and if it occurs on a scale that could have significant effects on the overall environment.

Many species, from earthworms to mussels, inevitably eat plastic particles. Callaghan wanted to know if the mosquitoes would do it and they would keep the pollutants throughout their life cycle. His team exposed the mosquito larvae to two sizes of fluorescent polystyrene particles (two and 15 microns, roughly the size of a Escherichia coli bacteria and 1.5 human blood cells, respectively) and then put them in clean water. When the researchers dissected several larvae, they found the microplastics in their bowels. The team dissected more mosquitoes once they became pupae, as well as adults – and always found microplastics in the kidney equivalent of insects. "So what they ate in larvae stayed in the digestive system," says Callaghan.

The number of particles found has decreased at each stage of development; Callaghan says that this might suggest that mosquitoes excrete some of what they eat at the larval stage and again as soon as they become adults. But further research would be needed to confirm this intuition.

According to Martin Wagner, an ecotoxicologist at the Norwegian University of Science and Technology, as is often the case with researchers in ecotoxicology at the Norwegian University of Science and Technology, the amount of plastic to which the larvae have been exposed not involved in the new study. The amount found in mosquitoes was also relatively low, he notes. One of Wagner's PhD students performed an experiment similar to that of Callaghan – although with a midge species and lower microplastic concentrations – and did not find the same retention for life, he says.

Callaghan says that one of the next steps in this research will be environmental sampling of mosquitoes from areas polluted by microplastics, to see if they found the same evidence of transfer between different stages of the life they did at the laboratory. She also wants to see if this happens with other insects that undergo such metamorphoses.

The team has found no indication that microplastics affect the survival rates of the mosquitoes themselves. But the results raise concerns about mosquito larvae that could take microplastics at the bottom of a pond, for example, and possibly transfer them to birds, bats and other terrestrial animals that feed on adult insects, sending them in food. chain. "There is no other way they would use to pick up these plastics," Callaghan said.

Microplastics growing in the gut of an animal could reduce its appetite, potentially reducing its growth and reproduction, which has been demonstrated in some species. But unlike pollutants such as mercury, it is unclear how easily microplastics can escape the intestine and reach other organs. And microplastics come in a wide variety of sizes, shapes and types of polymers, which could have equally diverse impacts. Wagner also points out that mosquitoes and other animals are also exposed to many natural particles that they can not digest, but that they have adapted to treat them, and it remains to be seen if microplastics will have a different result.

Callahan thinks that it is unlikely that mosquitoes will transfer microplastics to humans or other animals via their bites; for this to happen, the plastic particles will have to make their way to the salivary glands of the insects. On the contrary, she says, "I think the human angle is about the effect of humans – it's the effect humans have on ecosystems.