As honeybees make their way through the world, they are ideally suited to pick up bits and pieces of it along the way. Bees are covered with hairs that have evolved to hold tiny particles that the bee collects intentionally or simply encounters in its daily travels. These hairs become electrostatically charged in flight, which helps attract the particles. Pollen is the most obvious substance that gets caught up in these hairs, but so do plant debris, wax, and even bits of other bees.
Now, another material has been added to that list: plastics. Specifically, 13 different synthetic polymers, according to a study of honeybees and microplastics in Denmark. The study was published earlier this year in Science of the Total Environment.
It’s well established that microplastics are spread extensively around the planet. Yet scientists are still learning how they move through the atmosphere. Sampling them is difficult and most research of airborne microplastics to date has been conducted at ground level, scientists say.
It turns out that honeybees—and all those hairy legs and bodies—provide a viable means for better assessing the distribution of windborne plastic fibers and fragments. Thanks to their large numbers and wide-ranging foraging, honeybees can be drafted as living probes of how microplastics are scattered around the world.
“This work demonstrates for the first time the possibility of using honeybees as a bioindicator for the presence of MPs (microplastics) in the environment,” the scientists say.
For decades, scientists have used bees as pollution sentinels, tracking heavy metals, pesticides, air pollution, and even radioactive fallout. But research into bees’ interactions with plastics, which also dates to the 1970s, has focused more on macro plastics than micro.
Leafcutter bees, for example, which are similar in size to European honeybees but solitary and found all around the world, have been shown to use their huge mandibles to cut half-moon shaped pieces out of plastic, just as they do from leaves and petals.
Scientists in Chile, Argentina, and Canada, and the United States have observed leafcutter bees collecting such bits from bags, packaging, and other plastic materials and lining their nests with them. In the United States U.S. a study suggested that the bees also cut nesting material from plastic flagging used for surveying or marking construction sites.
In the Denmark study, scientists gathered thousands of worker bees, which are all female, from 19 apiaries—nine in the center of Copenhagen and 10 in suburban and rural areas beyond the city. The researchers collected bees directly from the interior of their hives in the spring, when colonies were building up. Because bees interact with plants, water, soil, and air—all areas where microplastics accumulate—they had abundant opportunity to encounter plastics. The collection team wore clothing made of natural fibers and took other precautions to avoid contaminating the sample bees.
The bees were frozen to euthanize them, then washed and scrubbed to remove the particles attached to their legs and bodies. Using a microscope and infrared light, the particles were then sorted by size, shape, and material type.
Fifteen percent of the particles recovered were microplastics. Of those, 52 percent were fragments and 38 percent were fibers. Polyester was the dominant fiber, followed by polyethylene and polyvinyl chloride.The bees also picked up natural cotton fibers.
The city bees presented the highest counts of microplastics, as expected, since it’s known that urban areas contain the highest densities of microplastics. The surprise was that the counts of microplastics on suburban and rural bees were not much lower. That suggests that wind dispersion evens out the concentration of microplastics over large areas, the scientists say.
“I would have expected more ‘clean’ bees in the countryside than in central Copenhagen,” Roberto Rosal, a professor of chemical engineering at the University of Alcalá in Madrid and a co-author of the study, said in an email. “But the high mobility of small microplastics offers an explanation for it.”
Is plastic pollution harming bees?
The question of how exposure to plastics is affecting bees is still open. Scientists are divided over whether nest-building with plastic bits by leafcutter bees is simply evidence of the bees adapting to the presence of a new material or whether it ultimately may prove harmful.
In a study published earlier this year in the Journal of Hazardous Materials, scientists in China sought to assess the potential risks that microplastics pose to honeybees. They fed honeybees polystyrene microplastics for two weeks and found it did not change their mortality rate. It did however alter the bees’ microbiome—the assemblage of gut bacteria essential to basic biological functions—in a way that the Chinese team concluded might present “substantial health risks.”
In particular, the team found that the bees’ death rate shot up from less than 20 percent to around 55 percent when the bees consumed a combination of polystyrene and tetracycline, a common antibiotic used in beekeeping to prevent a larval disease. “In isolation, microplastics might not be the most toxic contaminant, but the existence of other chemicals might increase their toxicity,” the Chinese researchers concluded.
Illaria Negri, a researcher at the Università Cattolica del Sacuro Cuore in Italy, who was not involved with either the Denmark or China studies, expressed similar concerns. The toxic effects of microplastics “could be magnified when they occur in combination with other pollutants, such as pesticides, veterinary drugs, plastic additives,'' she said in an email.
Certain pesticides can be absorbed by plastic debris, Negri said, and could have “devastating effects” on the health of bees and other wildlife and insects if ingested.