You eat them. Fish eat them. Even birds and frogs eat them. In fact, we all scarf them down like condiments. And when we’re not busy swallowing colorful bits of plastic, we inhale them, sending beads and fragments into the deepest recesses of the human lung.1 From there, some of the smaller particles ride the waves of our circulatory system as if it were a high-tech water park with twists and turns, slides and slumps.2
If all of us earthlings bathe in a soup of foreign particles, it follows that honey bees do, too. I’m referring to microplastics, those tiny but ubiquitous pieces of trash that we’ve unleashed into every known environment, from the bottom of the sea to the top of the highest mountain.3
The news on these stable compounds is not good. So far, most of the research on microplastics has centered on the oceans where they proliferate throughout the food chain. But a recent study even found pigmented microplastics in human placentas, potentially interfering with normal fetal development.4 And if they damage fish, clams, and crabs, if they foul the intestines of birds and frogs, what are they doing to our bees? The fact is, we know little.
What is a microplastic?
Microplastics are tiny pieces of plastic debris — chunks and shreds measuring less than 5 mm long — that move willy-nilly throughout our environment. Their smaller next-of-kin, the nanoplastics, which measure less than 1 mm, often accompany the larger particles. Both types are small enough to float in the air and water, worm their way through tiny filters, and remain invisible to most of the creatures that consume them.
When we think of plastic waste, we often picture the big stuff: water bottles, milk jugs, produce boxes, and shopping bags. Microplastics, at least in part, derive from these larger things as they decompose. One of the most alarming sources is car tires that shred slowly as they wear against the pavement and produce countless airborne particles. But we make some microplastics from scratch, such as the synthetic fibers of our clothes, carpets, rainwear, and shoes.
Researchers have found that the shape of the particles influences their behavior inside the bodies of animals. Spherical shapes roll over each other, slipping and sliding like marbles. Since they don’t form mats or clogs, they are less destructive to living organisms. But many microparticles are fibers and irregular fragments that stick together and form blockages. Long threads can coil and capture other particles in a net-like wad. Flat fragments may stick like Velcro instead of sliding past each other, and they sometimes have rough or sharp edges that can tear into living cells.
We know microplastics damage birds and fish by accumulating in their digestive tracts. They may consume the particles directly from the water, but more likely they consume them in the bodies of their prey. Larger animals eat the smaller ones after the smaller ones consumed microplastics from water or soil.
The guts of aquatic invertebrates, whose larval stages often eat tiny waterborne flora and fauna, ooze with rainbow bits of plastic. And as you might expect, filter feeders such as mussels, clams, and oysters can be rich sources of plastic for larger animals to feed on.
Not plastic alone
Another worrisome aspect of microplastics is the chemical additives that go into them. For example, plasticizers that provide certain qualities are added during manufacture. Depending on the application, the plastic may need to be stiff, soft and pliable, or transparent. An array of plasticizers help achieve these goals.
In addition, other chemicals — not defined as plasticizers — used in the manufacture of plastics may be dangerous to living things. Bisphenol A, for example, used to produce polycarbonate plastic and epoxy resins, has been scrutinized for several years as a potential endocrine disrupter.5
Regardless of their purpose or classification, many of these substances migrate into the environment as the material degrades. What worries scientists is our lack of knowledge of how these particles and leachates affect the life forms that consume and breathe them.
The shape of particles also plays a role in the release rate of chemicals. Fragments and fibers have more surface area compared to spheres, meaning they may release their chemical constituents more quickly. A quicker release could increase the dose to vulnerable species.
Plants and plastics
Some estimates suggest humans consume about 52,000 plastic particles per year and inhale another 74,000.6,7,8 Although they contaminate the environment where we live — including all sources of air, water, and soil — they also contaminate much of our food.
Research shows that plant roots can absorb plastic from the soil and send it to the vegetative parts of a plant, beginning with shoots and stems.9 Once inside the vascular system, plastics can travel throughout the plant, reaching the edible tubers, leaves, and fruits. The smallest particles are then distributed to the nectar, pollen, honeydew, and resins. Soils treated with sludge and manure — a common practice — are especially high in microplastic and nanoplastic particles.
Given the ubiquitous nature of these plastics in plants, it’s not surprising we find them in honey. A study in Ecuador found that 12% of honey samples contained plastic particles, and a study in Denmark found microplastics in honey samples from both suburban and rural apiaries.10
What do all these synthetic “food additives” mean for the bees? Although the particles are small, so are bees. For reference, the average honey bee worker ranges from 15 to 18 mm long, meaning a 5 mm microplastic fiber could be a third of her length — the equivalent of a six-foot man harboring a 24-inch plastic worm. Of course, the shape of particles will influence how readily they are ingested, but many are fine filaments, much longer than wide, released from synthetic textiles.
An anecdotal story
Two years in a row, I had a beehive behind our pump house, nestled against the wall. The building contains a thousand-gallon holding tank for water, as well as a washer and dryer. The building is insulated, although an IR camera reveals heat leaks from the intersection of the walls and floor. I figured the heat might be a boon to the bees during our cold, damp winters, so I didn’t worry about it. Nor did I worry about the dryer vent on the opposite side of the building.
During the first year, the colony in that hive produced a bumper crop of honey but collapsed during the winter. My postmortem showed nothing amiss — no obvious disease or distress — so I installed a second colony in the same hive. Once again, it produced masses of honey but died during the winter. I still couldn’t find any obvious reason for the loss, and since the rest of my colonies were fine, I gave up on that location.
But now, years later, I wonder if the ….