Chemicals from plastic bag pollution could unbalance lake ecology

Bacterial productivity in Scandinavian lakes has been boosted by leachate from plastic bags, but that’s not necessarily good news for aquatic ecosystems


July 26, 2022

A lake in Norway that was part of the study

SG Woodman

Plastic pollution could disrupt the ecology of lakes and rivers by leaching chemicals that promote the proliferation of bacteria, which unbalances the aquatic ecosystem.

Eleanor Sheridan at the University of Cambridge and his colleagues compared the impact of chemical compounds leached from cut-out shopping bags from various stores. The plastic pieces were added to water samples taken from 29 Scandinavian lakes in 2019. The group found that bacteria exposed to leachate from the bags grew on average at more than double the rate of bacteria in control samples from ‘distilled water.

If reproduced in nature, the increase in bacteria could stimulate the aquatic food web by providing food for other organisms. But Sheridan says that doesn’t mean plastic pollution is good news for fish populations at the top of the web. “Yes, you are going to benefit certain species of bacteria, but you are definitely going to upset the whole balance of species in the ecosystem. And that’s not a good thing at all,” she says.

The team based the plastic leachate levels on concentrations found in a study of Swiss lakes, but the amount added in the experiment may have been a sweet spot that promotes growth. Other studies have shown that higher concentrations can be toxic to bacteria. “So we may have hit that kind of low threshold that is able to benefit growth,” Sheridan says.

The study comes with some caveats. Although lakes of a wide range of sizes were tested, all were from Scandinavia. The team also did not test different leachate concentrations and only tried with low-density polyethylene (LDPE) rather than other plastic leachates.

However, the LDPE from bags is the biggest pollutant of water bodies. People should be aware of the unintended consequences of plastic waste and prevent it from entering the wider environment, Sheridan says. “We’re focusing much more on the macro-level type, and it’s important for people to also be aware that there can be this chemical effect on a much smaller scale on species in an ecosystem,” she says.

Journal reference: Nature Communication, DOI: 10.1038/s41467-022-31691-9

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Bryce K. Locke