Turns out, not all microplastics are created equal.
Although the term typically encompasses any plastic fragment with a diameter of 0.2 inches or less, microplastics can stem from anything from a polyester hoodie that sheds thousands of tiny filaments every time it’s laundered to a facial scrub that uses microbeads as a means of mechanical exfoliation.
But microfibers from synthetic clothing might be the greater evil, at least when it comes to damaging for marine life, warned the European Commission in its latest Science for Environment Policy bulletin.
Published last month, the news alert cited a 2017 study by the International Union for Conservation of Nature (IUCN) that compared the effects of microplastic polyester fibers and polyethylene beads on the survival, growth and reproductive health of Ceriodaphnia dubia, a common species of water flea that lives in freshwater lakes, ponds and marshes around the world. Researchers placed C. dubia into water-filled beakers that contained different concentration of either microbeads (0.5 to 16 milligrams per liter) or microfibers (0.125−4 mg/l) for a period of 48 hours. To serve as controls, some C. dubia were placed in beakers containing just water or water mixed with a solvent.
To examine the effects of chronic exposure, researchers also left C. dubia in beakers that contained smaller concentrations of microbeads (62.5 to 2,000 micrograms per liter) or microfibers (31.25 to 1,000 μg/l) for eight days. Meanwhile, control organisms were left in beakers of water and solvent for the same amount of time.
Both the polyester fibers and the polyethylene, scientists found, were toxic to C. dubia. Although short-term exposure to the highest concentrations of both types of microplastics proved particular lethal (4 mg/l for microfibers and 8 mg/l for microbeads), IUCN allowed that these concentrations are unlikely to be found in nature. The study did find, however, that long-term exposure to lower concentrations of plastics, including those seen in nature, caused deformities, stunted growth and interfered with the water flea’s ability to reproduce.
While C. dubia had to be exposed to a microbead concentration of 1,000 μg/l for its offspring numbers to be significantly curtailed, as well as 2,000 μg/l to shrink adult body size, a microfiber concentration of 500 μg/l was enough to do the same.
Exposing a water flea to a concentration of 1,000 μg/l of polyethylene beads, for instance, resulted in 56 percent fewer young than a flea from the control beaker. Exposing it to the same concentration of polyester fibers, on the other hand, led to 84 percent fewer offspring.
“Interestingly, the fibers were more toxic to the water flea than the beads,” the bulletin noted. “Whilst chronic exposure to both beads and fibers reduced the crustaceans’ body size and the number of young they produced, this effect was greater for fibers.”
IUCN researchers had a couple of ideas why this happened. C. dubia tends to mistake microbeads for food, a theory that bore out when they peered into the organisms’ stomachs to find them full of tiny white polyethylene beads. The higher the concentration of microbeads the water fleas were exposed to, the fuller their stomachs were.
“A full stomach could stop the organisms from eating real food, depriving them of vital energy,” the bulletin’s authors wrote. “With depleted energy reserves, C. dubia may be forced to invest more in survival rather than growth and reproduction, resulting in a reduced number of offspring.”
Microplastic fibers, however, were not taken up as food, scientists said. Instead, they appeared to interfere with the water flea’s ability to swim. At high concentrations, organisms became “entangled and immobilized” in the fibers, IUCN said. A microscope revealed that prolonged exposure to even lower concentrations of microfibers produced deformities in C. dubia’s shell and antennae. The stress of physical contact with the fibers, and the resulting damage, might explain the stunted reproduction and growth, researchers surmised.
The study is important because it’s the first to show the “serious harm” microfibers can inflict on aquatic animals, the European Commission said. For the most part, policymakers across the globe, including in the United States and Europe, have focused on microbeads. Individual EU member states that have banned or are planning to ban microbeads in cosmetics and personal-care products include Finland, France, Ireland, Luxembourg, Sweden and the United Kingdom.
“However, this research suggests microfibers from our clothes may be just as harmful, if not more so,” added the European Commission, which announced in January an inaugural Europe-wide strategy on plastics, including actions to restrict the intentional addition of microplastics to products and to ameliorate microplastic pollution from sources such as tires, textiles and pre-production plastic-resin pellets.
Other attempts at stemming microplastic waste might be forthcoming.
“In the follow-up to the plastics’ strategy and, taking into account the above-mentioned study, the Commission will examine which additional legislation or measures will be needed to address the specific problems presented by microfibers,” it said.