Some naturally produced lake bacteria grow quicker and more effectively on the remnants of plastic bags than on natural matter such as leaves and twigs, according to a study of 29 European lakes.
Bacteria degrade the carbon compounds in plastic to use as food for growth.
According to the researchers, imbuing waters with specific species of bacteria could be a natural way to eliminate plastic environmental contamination.
The effect is dramatic: when plastic pollution increased the total carbon level in lake water by just 4%, the percentage of bacterial growth more than doubled.
The findings suggest that plastic pollution in lakes is “priming” bacteria for rapid development, as the bacteria not only deteriorate the plastic but also are better able to break down other leftover carbon compounds in the lake.
Lake bacteria were discovered to prefer plastic-derived carbon compounds to natural carbon compounds. According to scientists, this is because the carbon compounds in plastics are convenient for bacteria to break down and use as food.
The researchers are quick to point out that this does not excuse ongoing plastic pollution. Some of the compounds found in plastics can be toxic to the environment, especially at high concentrations.
The results are published in the journal Nature Communications.
It’s almost like the plastic pollution is getting the bacteria’s appetite going. The bacteria use the plastic as food first, because it’s easy to break down, and then they’re more able to break down some of the more difficult food—the natural organic matter in the lake.
Dr. Andrew Tanentzap, Study Senior Author, Plant Sciences, University of Cambridge
“This suggests that plastic pollution is stimulating the whole food web in lakes because more bacteria means more food for the bigger organisms like ducks and fish,” he added.
The effect varied based on the diversification of bacterial species existing in the lake water; lakes with more diverse species were better at removing plastic pollution.
The researchers noted that European lakes are promising hotspots of microplastic pollution in a study published last year.
When plastics degrade, they emit simple carbon compounds. The scientists found that these carbon compounds are chemically distinguishable from the carbon compounds released when organic matter such as leaves and twigs decompose.
Plastic carbon compounds were found to be derived from additives distinctive to plastic products, such as adhesives and softeners.
In addition, bacteria eliminated more plastic pollution in lakes with fewer unique natural carbon compounds, according to the new study. This is because the bacteria in the lake water had fewer other sources of food.
The findings will aid in prioritizing lakes where pollution control is most critical. If a lake has a bunch of plastic pollution but not a lot of bacterial diversity and natural organic compounds, its ecosystem will be more susceptible to damage.
Unfortunately, plastics will pollute our environment for decades. On the positive side, our study helps to identify microbes that could be harnessed to help break down plastic waste and better manage environmental pollution.
David Aldridge, Professor, Zoology, University of Cambridge
Aldridge was also involved in the study.
Between August and September 2019, almost 29 lakes in Scandinavia were sampled for the study. These lakes varied in latitude, depth, area, average surface temperature, and the diversity of dissolved carbon-based molecules to evaluate several scenarios.
The researchers cut up plastic bags from four major UK retailers and shook them in water to release carbon compounds.
Glass bottles were packed with lake water at each lake. To depict the quantity of carbon dioxide leached from plastics into the environment, a small amount of “plastic water” was incorporated into half of these, and the same quantity of distilled water was added to the others. The bacterial activity was evaluated in each bottle after 72 hours in the dark.
The study assessed bacterial growth by mass increase and bacterial growth performance by the level of carbon released during the growth period.
The bacteria had doubled in size in the water containing plastic-derived carbon compounds. In 72 hours, approximately half of this carbon was incorporated into the bacteria.
“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 in the University of Cambridge’s Department of Plant Sciences, and study first author who undertook the research as part of a final-year undergraduate project.
The European Research Council funded the research.
Sheridan, E. A., et al. (2022) Plastic pollution fosters more microbial growth in lakes than natural organic matter. Nature Communications. doi.org/10.1038/s41467-022-31691-9.