Some naturally-occurring bacteria grow faster on the remains of plastic bags than in organic matter like twigs and leaves, according to a study published in the journal Nature Communications. The authors from the University of Cambridge, UK, defend that enriching waters with these particular species could be a natural way to eliminate plastic pollution.
The study was done with samples from 29 lakes across Scandinavia between August and September 2019. To assess a wide range of conditions, lakes sampled covered different latitudes, depths, areas, average surface temperature, and diversity of carbon-based molecules. For each location, researchers cut up plastic bags, mixed them with the water samples, and measured bacterial growth after a few days.
It turned out that these bacteria can use carbon compounds present in plastic as food to support their growth. Even when the level of plastic in the water was raised by just 4%, the rate of bacterial growth more than doubled. They grow faster in response to the presence of plastic and not only break down the carbon in plastic but are also better at degrading other forms of natural carbon present in the lake. The authors suggest that this preference for plastic is because these carbon compounds are easier to break down and use as food. However, the team is quick to highlight that this does not condone the ongoing plastic pollution. Some of the compounds can be extremely toxic to the environment and cannot be degraded by these bacteria.
“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,” said Dr. Andrew Tanentzap at the University of Cambridge’s Department of Plant Sciences, senior author of the paper. “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.”
Curiously, when bacteria break down plastic, they release simple carbon compounds, which differ from those released when bacteria digest organic matter. The compounds derived from plastic come from specific additives unique to plastic products, including adhesives and softeners.
The authors are hopeful that these results can help to prioritise the fight against plastic pollution. If a lake is heavily polluted but has low bacterial diversity capable of digesting plastic, then this ecosystem is more vulnerable.
“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,” said Professor David Aldridge in the University of Cambridge’s Department of Zoology, who was involved in the study.
“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,” added Eleanor Sheridan in the University of Cambridge’s Department of Plant Sciences.
Sheridan, E.A., Fonvielle, J.A., Cottingham, S. et al. Plastic pollution fosters more microbial growth in lakes than natural organic matter. Nat Commun 13, 4175 (2022). https://doi.org/10.1038/s41467-022-31691-9