Microplastics have become a common type of water pollutant. And these pollutants can now become airborne in the bellies of mosquitoes, a new study shows.
Researchers in the United Kingdom recently found that mosquito larvae can eat tiny bits of plastic from the water in which they’re living. As the mosquitoes grow into adults, much of that plastic stays inside them. That means birds and bats that eat mosquitoes may be taking in a mouthful of plastic with every meal. And any other animal that eats those birds and bats is probably also getting a little microplastic with their meals.
“We don’t yet know how harmful the microplastics will be,” says Amanda Callaghan. However, she adds, “If we wait to find out, it may be too late to do anything about it.” Callaghan is a zoologist who works at the University of Reading in England. Her team’s new findings appeared in the September Biology Letters.
Munching on microplastics
Microplastics are any bits of plastic smaller than half a centimeter (0.2 inch) across. In recent years, scientists have been finding these plastic bits in water all over the world. They tend to enter rivers as wastewater pollutants. From those rivers, they can drain into lakes and the ocean. Affected water can include sites where mosquitoes lay their eggs.
To find out what effects this might have, a member of Callaghan’s team, Rana Al-Jaibachi, fed microplastics to mosquito larvae in the lab. Larvae are the worm-like young of certain insects. Larvae often are adapted to survive very different environments than those they’ll live in as adults. Adult mosquitoes live in the air, for instance. Their larvae, however, hang out in small pockets of still water. There they gobble up algae and bacteria that live on the water’s surface.
In the lab, Al-Jaibachi put ground-up guinea pig food in the water where the larvae were growing. She added tiny beads of plastic. In total, she gave microplastic beads to 150 larvae.
To find out whether the larvae had gobbled up any microplastic, she randomly chose 15 larvae to examine. She selected 15 more mosquitoes after they’d grown into adults. Next she counted the number of beads in each insect.
“We counted the beads by grinding up the mosquito, filtering out the beads and looking down a microscope,” explains Callaghan. The plastic particles were too small to be ground up along with the animals’ tissue. And the beads were fluorescent, so they glowed green under blue light.
Microplastics showed up in all 30 mosquitoes, both larvae and adults. But the larvae hosted more of them. On average, each larva held more than 3,000 2-micrometer-wide beads. (A micrometer is one ten-thousandth of a centimeter.) The adults only had about 40 beads each. The researchers now suspect the mosquitoes may pee out some microplastics as they grow up.
Callaghan says the lesson from her team’s study is that microplastics are everywhere. “They can even move up into the air if they are eaten by an animal that can fly,” she concludes.
Marcus Eriksen is an environmental scientist at the 5 Gyres Institute in Los Angeles, Calif. There, he studies plastic pollution in oceans and lakes. And he would like to know how microplastics move through the environment outside of the lab.
The study by Callaghan’s team is helpful, he says, because it shows microplastic can stay in the bodies of mosquitoes as they grow into adults. “Now it's time to move to a real population of mosquitoes in nature and real quantities of plastic in the environment,” he says. “If we see an effect, then we've got something to act on.”
Cause for concern
How might mosquito larvae end up gobbling plastic in the wild? There are many ways microplastics can get into the lakes, ponds and puddles where mosquitoes lay their eggs. Some bits come from larger pieces of plastic that can break down in landfills and large bodies of water. Sunlight and waves help break these pieces into tiny bits.
Some clothing can shed microplastics, too. Fabrics such as fleece and nylon are made from plastic. When washed, they release bits of plastic lint into the wash water. This lint can then travel down household drains and into rivers, lakes and oceans.
Some companies also add tiny plastic beads to toothpastes and skin-care products. These beads help scrub away tooth plaque and dead skin cells. Then they, too, wash down the drain.
Plastics are made from many different chemical ingredients. Scientists still don’t know how many of these ingredients might affect human health. Plastics can also act like a chemical sponge, soaking up other pollutants from the water around it. For example, pesticides and other toxic compounds have turned up in plastics floating in water.
Callaghan’s study is concerning because it shows we can’t escape microplastics, says Kennedy Bucci. She is a PhD student in Canada at the University of Toronto. She studies how microplastic pollution affects freshwater organisms.
“We already know that microplastics are found in our oceans, lakes, rivers, agricultural fields and soil,” she says. “But now this study suggests that they can also be found in our skies.”
algae Single-celled organisms, once considered plants (they aren’t). As aquatic organisms, they grow in water. Like green plants, they depend on sunlight to make their food.
average (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.
bacteria (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals).
bat A type of winged mammal comprising more than 1,100 separate species — or one in every four known species of mammal.
biology The study of living things. The scientists who study them are known as biologists.
birds Warm-blooded animals with wings that first showed up during the time of the dinosaurs. Birds are jacketed in feathers and produce young from the eggs they deposit in some sort of nest. Most birds fly, but throughout history there have been the occasional species that don’t.
cell The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
compound (often used as a synonym for chemical) A compound is a substance formed when two or more chemical elements unite (bond) in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.
environment The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).
fabric Any flexible material that is woven, knitted or can be fused into a sheet by heat.
fluorescent (v. fluoresce) Adjective for something that is capable of absorbing and reemitting light. That reemitted light is known as fluorescence.
freshwater A noun or adjective that describes bodies of water with very low concentrations of salt. It’s the type of water used for drinking and making up most inland lakes, ponds, rivers and streams, as well as groundwater.
guinea pig A rodent (Cavia porcellus) often kept as pets or used in research. Colloquial: A person or other animal that is used as an experimental subject.
gyre (as in the ocean) A ringlike system of ocean currents that rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. Many of the biggest, most persistent gyres have become collection sites for floating long-lived trash, especially plastic.
insect A type of arthropod that as an adult will have six segmented legs and three body parts: a head, thorax and abdomen. There are hundreds of thousands of insects, which include bees, beetles, flies and moths.
landfill A site where trash is dumped and then covered with dirt to reduce smells. If they are not lined with impermeable materials, rains washing through these waste sites can leach out toxic materials and carry them downstream or into groundwater. Because trash in these facilities is covered by dirt, the wastes do not get ready access to sunlight and microbes to aid in their breakdown. As a result, even newspaper sent to a landfill may resist breakdown for many decades.
larva (plural: larvae) An immature life stage of an insect, which often has a distinctly different form as an adult. (Sometimes used to describe such a stage in the development of fish, frogs and other animals.)
micrometer (sometimes called a micron) One thousandth of a millimeter, or one millionth of a meter. It’s also equivalent to a few one-hundred-thousandths of an inch.
microplastic A small piece of plastic, 5 millimeters (0.2 inch) or smaller in size. Microplastics may have been produced at that small size, or their size may be the result of the breakdown of water bottles, plastic bags or other things that started out larger.
microscope An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.
nylon A silky material that is made from long, manufactured molecules called polymers. These are long chains of atoms linked together.
organism Any living thing, from elephants and plants to bacteria and other types of single-celled life.
particle A minute amount of something.
pesticide A chemical or mix of compounds used to kill insects, rodents or other organisms harmful to cultivated plants, pets or livestock; or unwanted organisms that infest homes, offices, farm buildings and other protected structures.
PhD (also known as a doctorate) A type of advanced degree offered by universities — typically after five or six years of study — for work that creates new knowledge. People qualify to begin this type of graduate study only after having first completed a college degree (a program that typically takes four years of study).
plaque (in dental medicine) A biofilm, or community of bacterial species, that grows on teeth and other surfaces in the mouth.
plastic Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.
pollutant A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.
population (in biology) A group of individuals from the same species that lives in the same area.
sponge Something that sops up liquids or other materials and holds them until squeezed out or removed in some other way. (in biology) A primitive aquatic animal with a soft, porous body.
tissue Made of cells, it is any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.
toxic Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.
United Kingdom Land encompassing the four “countries” of England, Scotland, Wales and Northern Ireland. More than 80 percent of the United Kingdom’s inhabitants live in England. Many people — including U.K. residents — argue whether the United Kingdom is a country or instead a confederation of four separate countries. The United Nations and most foreign governments treat the United Kingdom as a single nation.
wastewater Any water that has been used for some purpose (such as cleaning) and no longer is clean or safe enough for use without some type of treatment. Examples include the water that goes down the kitchen sink or bathtub or water that has been used in manufacturing some product, such as a dyed fabric.
wave A disturbance or variation that travels through space and matter in a regular, oscillating fashion.
Journal: R. Al-Jaibachi, R.N. Cuthbert and A. Callaghan. Up and away: Ontogenic transference as a pathway for aerial dispersal of microplastics. Biology Letters. Vol. 14, Sept. 19, 2018, p. 20180479. doi: 10.1098/rsbl.2018.0479.