Some of the world’s oceans are so polluted with plastic waste that huge garbage patches have formed there. But lakes are also affected, even if you don’t always see it at first glance. As researchers have now found, there are even more microplastics in some lakes – including Lake Maggiore in Italy and Lake Lugano in Switzerland – than in the world’s most polluted subtropical ocean. They must therefore not be overlooked when it comes to environmental protection, according to the scientists.
Plastic waste doesn’t rot if you throw it down the embankment or into the sea. Instead, over time, countless tiny plastic particles come loose from the bags, bottles and packaging, some of which can no longer be seen with the naked eye. They become microplastics. The pieces of plastic, which are less than five millimeters in size, pose a risk to health and the environment. For example, they have already been detected in our brain and liver, but also in many marine animals.
On the lookout for microplastics in 38 lakes
While gigantic garbage patches in the world’s oceans make it clear at first glance how serious the microplastic situation is there, the situation in lakes has not been documented in a uniform way so far. But researchers led by Veronica Nava from the Italian University of Milan-Bicocca have now also examined the condition of these inland waters for the first time in a globally representative and standardized manner. In total, the research team sampled 38 lakes in 23 countries, covering a spectrum of different water features – including area, depth and retention time of the water. Human factors such as population density and the presence of sewage treatment plants were also taken into account when selecting the lakes.
The researchers filtered an average of 140 cubic meters of lake water per site and counted how many microplastic items were contained per cubic meter, but also what type of plastic they were, such as polyester or polyethylene. The team used a mesh size of 0.25 millimeters for their filters and thus primarily captured plastic particles between 0.25 and 5 millimeters in size. Smaller, possibly even more common plastic particles were therefore not recorded.
More polluted than the oceans
The result: The researchers found microplastics in each of the lakes they sampled – no matter how untouched and isolated it seemed at first glance. However, the intensity of microplastic pollution varied greatly. For example, while Lake Avery in the US state of Michigan had 0.01 particles per cubic meter, Lake Lugano in Switzerland led the ranking with more than ten particles per unit volume. Together with two other lakes – Lake Tahoe in California’s Sierra Nevada and Lake Maggiore in Italy – this lake thus exceeded the critical mark of five particles per cubic meter.
“These results are worrying in that these three lakes already have a higher microplastic load than the world’s most polluted subtropical ocean eddies,” says Katrin Attermeyer from the University of Vienna. Lake Stechlinsee in Brandenburg is just below this threshold and thus ranks fourth among the most heavily polluted lakes. Although its bank is largely natural and surrounded by beech forest, the researchers unexpectedly found many microfibers in it. “These are probably fibers from the bathers’ clothing,” reports Hans-Peter Grossart from the Leibniz Institute of Freshwater Ecology and Inland Fisheries. Across lakes, most plastic particles in the still waters consisted of either polyester, polypropylene, or polyethylene.
The research team was also able to determine in which types of water the microplastics were particularly concentrated. On the one hand, Nava and her colleagues observed that lakes in densely populated and urbanized areas were particularly badly affected, but on the other hand large lakes were also affected. The water stays in them for a relatively long time, which is why they become sinks for plastic, as the researchers explain. Lake Tahoe, for example, takes around 650 years to completely replace its existing body of water with inflow and outflow, which is why microplastics that have landed there stay for quite a while.
Drinking water quality and ecosystems at risk
According to the scientists, the research results are also worrying because many lakes are used as sources of drinking water. The microplastic does not simply remain in them, but sooner or later ends up in the bodies of the people living there via the drinking water. The top three – Lake Lugano, Lago Maggiore and Lake Tahoe – are also popular with bathers. In addition to the possible negative consequences for people who drink from these lakes or swim in them, the high concentration of microplastics also threatens aquatic organisms and with them entire ecosystems.
“Plastic that accumulates on the surface of bodies of water can fuel the release of methane and other greenhouse gases. Plastics in water can interact with the atmosphere, biosphere and lithosphere, potentially affecting biogeochemical cycles through mechanisms that are not yet understood,” explains Nava. She and her research colleagues therefore warn that still waters such as lakes should not be overlooked in the fight against the plastic flood.
Source: University of Vienna, Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB); Specialist article: Nature, doi: 10.1038/s41586-023-06168-4