Plastispheres: the plastic-based micro-ecosystems that menace Antarctica

(By Federico Citterich on 9th August 2024)

One of the world’s most pristine and remote environments must deal with the impacts of microbe-colonised microplastics that are threatening its ecological stability

“The problem is that most of them are not even visible to the naked eye,” says Dr Maurizio Azzaro, Head of the Polar Sciences Department of the Italian National Research Council, while adjusting the microscope lenses. As his eyes approach the eyepiece, he can feel the coldness of the metal, frosted by the freezing temperatures of Terra Nova Bay, Antarctica.

There it is. A red spot in a transparent expanse. An immensely small plastic fragment sitting in the water sample. Azzaro amplifies the lenses towards the particle. On it, thousands of microbes are present.

“When people think about plastic pollution, they probably imagine bottles and bags strewn along a street or a beach,” says Azzaro. “Yet, they often forget that plastic items can also degrade into smaller particles, known as microplastics.”

Microplastics are now found in almost every environment on Earth, such as water bodies, soil, and air, and have even reached the most pristine areas of the world, including Antarctica and its seas.

“The issue with microplastics is that they are so small that they can be easily transported by wind and other atmospheric agents from one part of the world to the other,” says Dr Angelina Lo Giudice, a researcher at the Italian National Research Council. “This is how some of these particles reach these extremely remote areas, including Antarctic seas.”

And once there, microplastics can be erroneously ingested by animals, entering the food chain and reaching its highest levels.

“But that happens only after microorganisms have colonised these particles,” says Lo Giudice. In aquatic environments, microplastics provide a stable, long-lived, and mobile environment onto which microbes can grow, and thus immediately adhere to them. This creates a new plastic-based micro-ecosystem, known as plastisphere.

Plastispheres host photosynthetic organisms, predators and preys, symbionts and parasites, enabling an incredible amount of potential interactions between the microorganisms that inhabit them. “They are fully-working ecosystems,” says Azzaro.

According to recent research, microbial communities living in plastispheres significantly differ from the free-living, independent communities of their surroundings.

“Plastispheres tend to host more consolidated and structured microbial communities,” says Dr Maria Papale, first author of the study. “While free-living microbial communities are exposed to variables that influence their composition – such as temperature, salinity, pH, solar radiation, presence of dissolved nutrients, etc. – plastisphere-colonising communities are protected by a solid and stable substrate.”

The plastic component of these microparticles can in fact act as a physical barrier, shielding microbes from direct exposure to external factors.

“Furthermore, microbes on plastic surfaces often form biofilms,” adds Lo Giudice, co-author of the study. “These are protective layers of cells and extracellular material that preserve the plastisphere-colonising communities even further.”

From an ecology standpoint, however, this is problematic. The presence of plastispheres alters microbial communities and, consequently, the balance of their environment, having a chain effect on the entire ecosystem.

“Plastispheres affect the normal functioning of nutrients cycles,” adds Papale. “This ultimately modifies the structure of all biological communities in the ecosystem, not just the microbial ones.”

“And we have to remember that these microscopic particles are ingested by a wide range of animals, either because they confuse them with preys or because they are already present in the organisms they eat,” explains Azzaro.

The effect is that animals at the base of the food chain ingest microplastics because they mistake them for food items. These animals are then eaten by predators, which in turn become prey for other predators, continuing up the food chain until reaching the top.

According to the scientists, this also creates problems in terms of the spread of pathogenic microbes.

“If pathogens adhere to a microplastic particle and this is then ingested by other organisms, the pathogens will transfer through the food chain and circulate more easily,” says Azzaro. “The same applies for heavy metals,” he adds.

In fact, microplastics can also attract and accumulate other pollutants such as heavy metals due to the chemical and environmental conditions of the water (e.g., salinity, pH, and temperature) and of the microparticle itself (e.g., chemical composition, surface area, size, and shape).

“On microplastics, we often detect the presence of industrially-derived heavy metals such as copper, lead, nickel, and chromium,” says Azzaro. “Clearly, the fact that these can easily spread through the food chain is very problematic.”

For example, a study by the University of Toronto reported for the first time the presence of microplastics in the Arctic char, a cold-water fish of the same family of the salmon and native to Arctic and sub-Arctic regions, including Northern Europe. The Arctic char is commonly used for human consumption, emphasising how microplastics can be a significant problem for us as well.  

“Microplastics can definitely impact humans as well,” explains Azzaro. “A lot of the food we eat and of the water we drink is contaminated by microplastics.” And if these contain heavy metals, those heavy metals will end up in our organism.

“Hence, it is imperative that we take urgent actions to mitigate and contrast microplastic pollution, even in remote areas such as Antarctica,” says Lo Giudice. “We need to monitor the presence and distribution of plastic material in polar regions, and we need to better evaluate the impacts they have on biodiversity.”

Recently, scientists have been focussing their attention on plastic-degrading microbes, microorganisms that have been observed ‘eating’ the plastic material they adhere to.

“Although plastics are a relatively new material in the history of the world, the chemicals they are made from – primarily components of oil – are not,” says Lo Giudice. “This means that microorganism had millions of years to develop mechanisms to degrade them.”

However, Azzaro explains that this procedure is extremely slow. “Currently, the process is not efficient enough to be used at a global scale,” he says. While plastic-degrading microbes constitute a promising prospect for the future, they are still far away from being used in industry.

“Often, these plastic-degrading microorganisms can’t even fully degrade microplastics,” says Lo Giudice. “This is because their efficiency can be influenced by biological factors such as the presence of specific microbial species.”

With this solution still far from being effective, Papale warns that we urgently necessitate alternative responses.

“We require immediate solutions both on a local and a global scale, and we need to understand the source and fate of plastic materials in Antarctic regions,” she adds.

At a microplastics conference held in Messina (Italy) in May, Papale suggested that polar research stations can be a source of pollution. “Field research is extremely important, but by traveling there we inevitably pollute those environments,” she says.

“Our study even demonstrates that plastispheres recovered from the surroundings of the Italian ‘Mario Zucchelli’ research station (Road Bay, Antarctica) grew abnormally, leading to a massive microbial abundance,” Papale adds.

According to the researchers, anthropogenic stressors influenced the chemical structure of the biofilm and the microbial composition in plastispheres around the station, promoting microbial growth even during winter, despite the hostile environment.

“This creates a paradox,” says Papale. “On the one hand, we need to conduct field research to understand and combat plastic pollution in Antarctica; on the other hand, however, the more we visit, the more we pollute and alter the ecosystem.”

“It’s a tough one,” says Azzaro bitterly chuckling. “However, field research has a number of benefits that outweigh its drawbacks.” Field studies are essential for accurately measuring the levels of microplastic pollution and for gathering data to inform policy and develop mitigation strategies.

“I will still need to venture there, I believe,” says Azzaro. “And I will still feel the icy grip of the frozen eyepiece as I approach the microscope,” he concluded. 

Feature photo: Photo by Bob Brewer on Unsplash