European lakes are microplastic pollution hotspots. Researchers have now investigated how this affects the bacteria in the lakes. According to this, various bacteria are able to break down the carbon compounds from plastic bags and the like and use them for their growth – even better than natural carbon compounds. The discovery could possibly help to curb the pollution of water bodies with microplastics by specifically colonizing plastic-degrading bacteria there. On the other hand, the massive bacterial growth stimulated by the plastic affects the entire food web of the lake – with potentially serious consequences for the ecosystem.
If plastic waste, such as shopping bags and packaging materials, ends up in the environment, it often accumulates in bodies of water such as lakes. Depending on the material and environmental conditions, it may take centuries for the plastic to largely decompose. Various chemicals are released during the degradation process. In addition to various toxins, this also includes simple carbon compounds. These come, among other things, from adhesives and plasticizers that are added to plastic products.
Samples from 29 Scandinavian lakes
A team led by Eleanor Sheridan from the University of Cambridge in Great Britain has now investigated the influence of plastic pollution on the growth of bacteria in lakes. To do this, the researchers took samples from 29 lakes in Scandinavia, which differed in terms of latitude, depth, area, temperature and amount of dissolved organic matter. To introduce controlled plastic pollution, the researchers cut up plastic bags from four major UK supermarket chains and left them in a bottle of distilled water under UV light that mimicked natural sunlight for a week.
A small amount of this plastic water was added to the seawater samples by Sheridan and her team. As a comparison, they also retained samples of untreated water from each lake. After 72 hours, during which the samples were stored in the dark, the researchers examined bacterial activity. To do this, they used the increase in mass to measure how much the bacteria had multiplied. On the other hand, they measured the efficiency of bacterial growth based on the amount of carbon dioxide released during growth.
Appetizer for bacteria
The result: “The plastic water increased the bacterial biomass by a factor of 2.29 when it was added to the samples from the surface water of the lakes in an environmentally relevant concentration,” the researchers report. The analyzes showed that various types of bacteria that occur naturally in the lakes even prefer to use the carbon compounds in plastic. “It’s almost as if the plastic pollution stimulates the bacteria’s appetite,” says Sheridan’s colleague Andrew Tanentzap. “The bacteria first use the plastic as food because it is easily degradable for them, and are then more able to break down the more difficult food – the natural organic matter in the lake.”
The degradation of the plastic carbon compounds was particularly effective when the water sample came from a lake with many different types of bacteria and contained few natural carbon compounds from organic material such as leaves and branches. From the authors’ point of view, these findings could possibly contribute to enriching lakes that are particularly polluted with plastic with certain bacteria in a targeted manner in order to facilitate the breakdown of the plastic. In the study, however, they did not investigate the extent to which the plastic could actually be degraded. Before they added the plastic water to the samples, they filtered out all the larger bag components so that only dissolved compounds remained in the water.
Impact on the food web
However, the bacterial growth promoted by plastic pollution could have serious effects on the lake ecosystem: “The results indicate that plastic pollution stimulates the entire food web in lakes, because more bacteria means more food for larger organisms such as ducks and fish,” says Tanentzap . Adds Sheridan, “Our study shows that tote bags entering lakes and rivers can have dramatic and unexpected impacts on the entire ecosystem. We hope that our results will encourage people to be even more careful when disposing of plastic waste.”
Source: Eleanor Sheridan (University of Cambridge, UK) et al., Nature Communications, doi: 10.1038/s41467-022-31691-9