Bacteria can remove plastic pollution from lakes – “Boosting the entire food web”

A freshwater lake in Norway, one of 29 European lakes that were part of the study. Credit: Samuel Woodman

Scientists have found that some naturally occurring lake bacteria grow faster and more efficiently on leftover plastic bags than on natural materials like leaves and twigs. Their study included 29 European lakes.

The carbon compounds in the plastic are broken down by bacteria and used as food for their growth.

According to the researchers, enriching waters with particular species of bacteria could be a natural way to remove plastic pollution from the environment.

“This suggests that plastic pollution stimulates the entire lake food web, as more bacteria means more food for larger organisms like ducks and fish.” — Dr. Andrew Tanentzap

The effect is pretty obvious: when plastic pollution increased the overall carbon level in the lake water by just 4%, the rate of bacterial growth more than doubled.

According to the findings, plastic pollution in lakes likely “primes” the bacteria for rapid growth – the bacteria not only break down plastic, but are then more capable of breaking down other naturally occurring carbon compounds in the lake.

It has been found that bacteria in the lake prefer plastic-derived carbon compounds to natural ones. Scientists believe this is because the carbon compounds in plastics are easier to break down and use as food for bacteria.

This does not tolerate ongoing plastic pollution, the researchers warn. This is because some of the compounds in plastics can have toxic effects on the environment, especially at high concentrations.

The results are published today (July 26, 2022) in the journal Nature Communication.

Study the lake in Norway

A freshwater lake in Norway, one of 29 European lakes analyzed in the study. 1 credit

“It’s almost as if plastic pollution is whetting the appetite of bacteria. Bacteria first use plastic as food because it is easy to break down, then they are more able to break down some of the more difficult foods – the lake’s natural organic matter,” said Dr Andrew Tanentzap of the University. . from Cambridge’s Department of Plant Sciences, lead author of the paper.

He added: “This suggests that plastic pollution stimulates the entire food chain in lakes, as more bacteria means more food for larger organisms like ducks and fish.”

The effect varied depending on the diversity of bacterial species present in the lake water – lakes with more different species were better at breaking down plastic pollution.

A study published by the authors last year found that European lakes are potential hotspots for microplastic pollution.

Eleanor Sheridan

Eleanor Sheridan from the University of Cambridge’s Department of Plant Science, first author of the study who undertook the work as part of an undergraduate graduation project. Credit: Samuel Woodman

When plastics break down, they release simple carbon compounds. The researchers found that these are chemically distinct from the carbon compounds released during the decomposition of organic matter like leaves and twigs.

Carbon compounds in plastics have been shown to come from additives unique to plastic products, including adhesives and softeners.

The new study also found that bacteria removed more plastic pollution in lakes that had fewer unique natural carbon compounds. This is because the bacteria in the lake water had fewer other food sources.

The results will help prioritize lakes where pollution control is most urgent. If a lake has lots of plastic pollution, but low bacterial diversity and lots of different natural organic compounds, then its ecosystem will be more vulnerable to damage.

“Unfortunately, plastics will pollute our environment for decades. On the positive side, our study is helping to identify microbes that could be harnessed to help break down plastic waste and better manage environmental pollution,” said Professor David Aldridge from the University of Cambridge’s Department of Zoology, who has participated in the study.

The study involved sampling 29 lakes across Scandinavia between August and September 2019. To assess a range of conditions, these lakes differed in latitude, depth, area, mean surface temperature and diversity of dissolved carbon-based molecules.

The scientists cut up plastic bags from four major UK retail chains and shook them in water until their carbon compounds were released.

At each lake, glass bottles were filled with water from the lake. A small amount of “plastic water” was added to half of them, to represent the amount of carbon leached from plastics into the environment, and the same amount of distilled water was added to the others. After 72 hours in the dark, bacterial activity was measured in each of the bottles.

The study measured bacterial growth – by increased mass and bacterial growth efficiency – by the amount of carbon dioxide released during the growth process.

In the water containing plastic-derived carbon compounds, the bacteria had doubled in mass very effectively. About 50% of this carbon was incorporated into the bacteria in 72 hours.

“Our study shows that when carrier bags enter lakes and rivers, they can have dramatic and unexpected impacts on the entire ecosystem. Hopefully our results will encourage people to be even more careful about how they dispose of plastic waste,” said Eleanor Sheridan of the University of Cambridge’s Department of Plant Sciences, first author of the study who undertook the work. within the framework of a final year. undergraduate project.

Reference: “Plastic pollution promotes microbial growth in lakes more than natural organic matter” July 26, 2022, Nature Communication.
DOI: 10.1038/s41467-022-31691-9