A study of 29 European lakes found that certain bacteria naturally present in lakes grow faster and more efficiently on leftover plastic bags than on natural materials such as leaves and twigs. The bacteria break down the carbon compounds in the plastic to use as food for their growth.
Given this discovery, scientists claim that enriching water with certain species of bacteria could be a natural way to remove plastic pollution from the environment, as published in the journal “Nature Communications”.
Furthermore, they point out that the effect is pronounced because the rate of bacterial growth more than doubled when plastic pollution increased the overall carbon level in the lake water by just 4%.
The results suggest that plastic pollution in lakes “primes” bacteria for rapid growth: not only do bacteria break down plastic, but they are more capable of breaking down other natural carbon compounds in the lake.
Bacteria in lakes have been found to favor plastic-derived carbon compounds over naturally occurring compounds. 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 since some of the compounds in plastics can have toxic effects on the environment, especially at high concentrations.
“It’s almost as if plastic pollution is whetting the appetite of bacteria,” says Dr Andrew Tanentzap, from the Department of Plant Science at the University of Cambridge, UK, lead author of the plastic paper. as food, because it is easy to break down, and they are then better able to break down some of the toughest foods: the lake’s natural organic matter. »
“This suggests that plastic pollution stimulates the entire lake food web, 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 broke down plastic pollution better.
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. Researchers have found that these are chemically different from the carbon compounds that are released when organic matter, such as leaves and twigs, decomposes.
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 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,” warns Professor David Aldridge, from the University of Cambridge’s Department of Zoology, who took part 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 the sampling of 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 molecular diversity. based on dissolved carbon.
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. Half of them had a small amount of “plastic water” added, 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 during the growth process.
In water containing plastic-derived carbon compounds, the bacteria doubled their mass very effectively. About 50% of this carbon was incorporated into the bacteria in 72 hours.
“Our study shows that when trash bags enter lakes and rivers, they can have a dramatic and unexpected impact on the entire ecosystem. Hopefully our results will encourage people to pay even more attention to how they get rid of plastic waste.” says Eleanor Sheridan, from the University of Cambridge’s Department of Plant Science, first author of the study, who carried out the work as part of a final project.