Some naturally occurring lake bacteria grow faster and more efficiently on the remains 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, enriching waters with specific species of bacteria could be a natural way to remove plastic pollution from the environment.
The effect is dramatic: when plastic pollution increased the overall carbon level in lake water by just 4%, the rate of bacterial growth more than doubled. The findings suggest that plastic pollution in lakes is ‘priming’ bacteria for rapid growth, as the bacteria not only break down the plastic but are also better able to break down other natural carbon compounds in the lake.
Lake bacteria were discovered to prefer plastic-derived carbon compounds over natural carbon compounds. According to the researchers, this is because the carbon compounds in plastics are easier for bacteria to break down and use as food.
The scientists 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 research was published in the journal Nature Communications.
Our research shows that when carrier bags enter lakes and rivers, they can have dramatic and unexpected effects on the entire ecosystem. Hopefully, our findings will encourage people to be even more cautious about how they dispose of plastic waste.
Eleanor Sheridan
“It’s almost as if the bacteria’s appetite is being stimulated by the plastic pollution. The bacteria eat the plastic first because it is easy to break down, and then they can break down some of the more difficult food — the natural organic matter in the lake, for example” Senior author of the paper is Dr. Andrew Tanentzap of the University of Cambridge’s Department of Plant Sciences.
He added: “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.”
The effect varied according to the diversity of bacterial species present in the lake water; lakes with more diverse species were more effective at breaking down plastic pollution. The authors discovered that European lakes are potential hotspots of microplastic pollution in a study published last year.
When plastics degrade, they emit simple carbon compounds. The researchers discovered that these carbon compounds are chemically distinct from the carbon compounds released when organic matter such as leaves and twigs decompose. Plastic carbon compounds were found to be derived from additives unique to plastic products, such as adhesives and softeners.
In addition, bacteria removed more plastic pollution in lakes with fewer unique natural carbon compounds, according to the new study. This is due to the fact that the bacteria in the lake water had fewer other food sources. The findings will aid in prioritizing lakes where pollution control is most critical. If a lake has a lot of plastic pollution but not a lot of bacterial diversity and natural organic compounds, its ecosystem will be more vulnerable to damage.
“Plastics, unfortunately, will pollute our environment for decades. On the plus side, our research contributes to the identification of microbes that could be used to help break down plastic waste and better manage environmental pollution “said David Aldridge, a researcher at the University of Cambridge’s Department of Zoology.
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 shopping chains, and shook these in water until their carbon compounds were released.
At each lake, glass bottles were filled with lake water. A small amount of the ‘plastic water’ was added to half of these, 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 mass increase and bacterial growth efficiency by the amount of carbon-dioxide released during the growing process. The bacteria had doubled in size in water containing plastic-derived carbon compounds. In 72 hours, roughly half of this carbon was incorporated into the bacteria.
“Our research shows that when carrier bags enter lakes and rivers, they can have dramatic and unexpected effects on the entire ecosystem. Hopefully, our findings will encourage people to be even more cautious about how they dispose of plastic waste” Eleanor Sheridan, first author of the study and a final-year undergraduate student at the University of Cambridge’s Department of Plant Sciences, said.
