Studies show that in 2018, 27 million tons of plastic went into American landfills. Containers and packaging accounted for the vast majority, even as consumers try their best to avoid plastics when shopping.
Although bioplastics have been deemed as a potential solution, a study published in the journal Environmental Science & Technology shows that they can also have a negative impact on the environment. According to the study, earthworms have a strong capability for consuming bioplastic derived from polylactic acid (PLA), which is typically made from plant-based sugars. Lei Wang, a professor at Nankai University, compared how earthworms interacted with various forms of plastic, as well as their ability to break them down. He found that the process doesn’t just end at decomposition.
The plastics exposed to wind, sun, and water in landfills break down into microplastics, which are then carried into oceans, food, and soil. As earthworms make tunnels in the soil, they eat the dirt to digest the organic matter, meaning that if contaminated with plastic, it can become part of the worms’ diets.
According to Wang, existing research does not support a significant difference between bioplastics and petroleum-based plastics in terms of environmental pollution, even though degradable and non-degradable plastics present different levels of risk.
“At present, the degradation of most biodegradable plastics in the natural environment is not as fast as people think, because such design will reduce their durability,” Wang explains. “But in general, they have a higher affinity for microorganisms than non-degradable plastics. This may imply differences in ecological and health risks associated with microorganisms.”
Wang and his team planted four materials in a test chamber: a fully fossil fuel-based plastic, a fully degradable and bio-based plastic, and two semi-synthetic plastics, and observed which was prefered by the earthworms to digest. Earthworms appeared to avoid the two semi-synthetic plastics, which were made with cellulose, while they tended to approach soil containing both the bio-based PLA plastic and fossil fuel-based PET plastic. They were able to break down PLA much easier than PET.
If PLA breaks down too easily, it would be dangerous in natural environments. Wang and his team found that most of the PLA had been degraded into nanoparticles, which are up to 1,000 times smaller than a micron. Although microplastics have been linked to potential health risks in recent years, bio-based microplastics and nanoplastics are understudied, a fact that Wang notes in his study.
“They can be left behind as particles, and they are long-lasting. It doesn’t matter if they are biodegradable. They will still act as a microparticle.”
“The impact chemicals have on the environment is really complex,” he says. “It’s not as simple as ‘bio-based is better than oil-based.’”
Wang hopes to continue research on the breakdown of bioplastics in soil. It’s unknown if the earthworms gain any nutritional value from digesting plastics made from PLA. The life cycle of bioplastics is a crucial factor to understand how the earth’s ecosystems are adapting to them, Wu says.
