Featured image: Plastic is working its way into every corner of the environment and into animals too. Researchers fed tiny “microplastic” fragments to mosquito larvae to see what happened next. Source: Wikimedia Commons/James Gathany, CDC.
Original Paper: Al-Jaibachi, R., R.N. Cuthbert, A. Callaghan. 2019. Examining effects of ontogenic microplastic transference on Culex mosquito mortality and adult weight. Science of the Total Environment. 651:871-876. https://doi.org/10.1016/j.scitotenv.2018.09.236
Plastics know no bounds
At first glance the edge of a pond might look like a boundary where the water ends and the land begins. But ecologists know that water and land are connected by a web of invisible bridges that continually pass energy and materials back and forth. Animals that start life in the pond—such as insects or salamanders—move to the land as adults where they feed terrestrial predators. Leaves drop into the pond, as do insects that fall from the air, and make their way into the aquatic food web. This give-and-take supports life in both realms. But what happens when pollutants enter the pictures – could they catch a ride and move between the worlds of water and air?
Plastics are among the most widespread and persistent pollutants on the planet. Most of us have seen dramatic images of plastic fragments amassing in the ocean, but this is not just an ocean problem. Tiny plastic particles—microplastics—are also accumulating in freshwaters, where many small animals are known to eat them.
Microplastics on the menu
Scientists in the United Kingdom discovered that mosquito larvae not only eat microplastics from their environment, but the particles also stay in their stomachs as the mosquito transitions through metamorphosis and into adulthood. When those insects become winged adults their internal stash of plastic particles also takes flight (1). Because mosquitoes are eaten by predators like birds, spiders, bats and more, the microplastics mosquitoes carry could make their way from freshwater into neighboring terrestrial food webs.
And how does having a stomach full of microplastics affect the mosquitoes themselves? In a more recent study, the same scientists found that despite having stomachs filled with microplastic particles, mosquitoes didn’t suffer negative effects. To discover this, researchers housed mosquito larvae in containers where they were exposed to microplastic fragments. The mosquitoes chowed down on the plastic, just as researchers expected. Then, as the larvae grew scientists monitored their development and survival. When they eventually became adults and emerged from the water, scientists measured their growth and weighed the microplastics in their stomachs. It was no surprise that the mosquitoes munched on microplastic particles. But what scientists didn’t expect is that eating plastic didn’t harm mosquitoes. They grew as much and survived as long as mosquitoes eating all-natural food.
The success of mosquitoes on polluted diets suggests that microplastics can flow from aquatic to terrestrial food webs through an open pipeline. If mosquitoes with plastic-filled stomachs are as likely to survive as those who stick to an organic diet, there is no natural control on the transport of plastics across this intricate boundary between water and land.
Plastics are here, there and everywhere
Microplastics originate from a vast array of synthetic products humans rely on but routinely discard or rinse down the drain—packaging, everyday household items and personal cosmetics. These tiny toxins lurk around every corner of the natural world. They drift through expanses or air over remote mountain tops (2) and stow away in the stomachs of the smallest animals. Studies like this one teach us that we are just starting to comprehend how vast the reach of these pollutants is and how widespread their effects on Earth’s biology could be.
- Al-Jaibachi, R., R.N. Cuthbert, A. Callaghan. 2018. Up and away: ontogenic transference as a pathway for aerial dispersal of microplastics. Biology Letters. 14:9. https://doi.org/10.1098/rsbl.2018.0479
- Allen, S. D. Allen, V.R. Phoenix, G. Le Roux, P. Durantez Jimenez, A. Simonneau, S. Binet and D. Galop. 2019. Atmosphere transport and deposition of microplastics in a remote mountain catchment. Nature Geoscience. 1752-0908. https://doi.org/10.1038/s41561-019-0335-5