Bacteria can remove plastic pollution from lakes
A study of 29 European lakes found that some naturally occurring lake bacteria grow faster and more efficiently on leftover plastic bags than on natural matter like leaves and twigs.
The bacteria break down the carbon compounds in the plastic to use as food for their growth.
Scientists say enriching waters with particular species of bacteria could be a natural way to remove plastic pollution from the environment.
The effect is pronounced: the rate of bacterial growth more than doubled when plastic pollution increased the overall level of carbon in the lake water by just 4%.
The results suggest that plastic pollution in lakes “primes” bacteria for rapid growth – the bacteria not only break down plastic, but are then more able to break down other natural carbon compounds in the lake.
It has been found that bacteria in the lake favor plastic-derived carbon compounds over naturally occurring compounds. Researchers believe this is because the carbon compounds in plastics are easier to break down and use as food for bacteria.
Scientists warn that this does not condone ongoing plastic pollution. Some of the compounds in plastics can have toxic effects on the environment, especially at high concentrations.
The results are published today in the journal Communication Nature.
“It’s almost as if plastic pollution is whetting bacteria’s appetites. Bacteria first use plastic as food because it’s easy to break down, and then they’re better able to break down some of the more difficult foods – natural food organic matter in the lake,” said Dr Andrew Tanentzap from the Department of Plant Science at the University of Cambridge, 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.
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 helps identify microbes that could be harnessed to help break down plastic waste and better manage environmental pollution,” said the professor. David Aldridge of the University of Cambridge Science Department. Zoology, who 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, average 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 pay even more attention to how which they dispose of as plastic waste,” said Eleanor Sheridan of the University. from Cambridge’s Department of Plant Science, first author of the study who undertook the work as part of an undergraduate graduation project.