A study of 29 European lakes has found that some naturally occurring bacteria in lakes grow more quickly and efficiently on the remains of plastic bags than on natural matter such as leaves and twigs. Bacteria break down the carbon compounds in the plastic to use as food for their growth.
Given this finding, scientists say that enriching the water with certain species of bacteria could be a natural way to eliminate plastic pollution from the environment, as published in the journal ‘Nature Communications’.
Furthermore, they highlight that the effect is pronounced as the rate of bacterial growth more than doubled when plastic pollution increased the overall level of carbon in the lake water by only 4%.
The results suggest that plastic pollution in lakes is “priming” bacteria for rapid growth: bacteria not only break down plastic, but are better able to break down other natural carbon compounds in the lake.
Bacteria in lakes were found to favor plastic-derived carbon compounds over natural ones. The researchers believe this is because the carbon compounds in plastics are easier for bacteria to break down and use as food.
Scientists warn that this does not justify continued plastic pollution, especially as some of the compounds in plastics can have toxic effects on the environment, especially in high concentrations.
“It’s almost as if plastic pollution whets the appetite of bacteria,” explains Dr Andrew Tanentzap, from the Department of Plant Sciences at the University of Cambridge, UK, lead author of the paper. plastic as food, because it’s easy to break down, and then they’re better able to break down some of the hardest food: the natural organic matter in the lake.”
“This suggests that plastic pollution is stimulating the entire food web in lakes, because more bacteria means more food for larger organisms like ducks and fish,” he says.
The effect varied depending on the diversity of bacterial species present in the lake water: those 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 discovered that these are chemically different from the carbon compounds that are released when organic matter, such as leaves and twigs, decomposes.
The carbon compounds in plastics are derived from additives unique to plastic products, such as 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 food sources.
The results will help prioritize the lakes where pollution control is most urgent. If a lake has a lot of plastic pollution, but little bacterial diversity and many different natural organic compounds, its ecosystem will be more vulnerable to damage.
“Unfortunately, plastics will pollute our environment for decades to come,” warns Professor David Aldridge, from the University of Cambridge’s Department of Zoology, who was involved in the study. “On the positive side, our study helps identify microbes that could be harnessed to help break down plastic waste and better manage environmental pollution.
The study included 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.
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 lake water. Half of them had a small amount of “plastic water” added to them, to represent the amount of carbon released from plastics into the environment, and the rest had the same amount of distilled water added. After 72 hours in the dark, the bacterial activity in each of the bottles was measured.
The study measured bacterial growth by increased mass and bacterial growth efficiency by the amount of carbon dioxide released in the growth process.
In water containing carbon compounds derived from plastic, the bacteria doubled their mass very efficiently. About 50% of this carbon was incorporated into the bacteria within 72 hours.
“Our study shows that when garbage bags enter lakes and rivers they can have a dramatic and unexpected impact on the entire ecosystem. Hopefully our results will encourage people to be even more careful about how they dispose of plastic waste.” “, says Eleanor Sheridan, from the Department of Plant Sciences at the University of Cambridge, first author of the study, who carried out the work as part of a final project.
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