Microplastic pollution levels in some freshwater lakes higher than in oceans
Microplastic pollution in freshwater lakes can reach levels that exceed those in the infamous ‘floating garbage patch’ ocean gyres, according to a new study. Microplastics are found in lakes and reservoirs all over the world, the study found, even in remote and mountainous locations.
The study, led by Dr. Veronica Nava and published in Nature, assessed plastic pollution in 38 lakes and reservoirs across six continents, each subject to different environmental conditions. They found microplastics – small fragments of plastic from clothing, packaging and other products – at all study sites.
Two types of lakes were found to be particularly vulnerable to microplastic pollution. First, those in densely populated and urbanised areas where human activity is intensive. Second, those with large watersheds, shorelines and water inflows, where plastic pollution has numerous routes to reach a lake across a wide area, and where water is retained for a long period of time.
“Our results provide the first comprehensive picture of microplastic pollution in lakes,” said co-author Professor Hans-Peter Grossart from IGB. “They highlight the importance of including lakes and reservoirs in the fight against microplastic pollution for pollution management and continued provision of lake ecosystem services.”
Polyester, polypropylene and polyethylene were the most common microplastics found by researchers, but the plastic ‘signature’ of each lake differed. Microplastics were found at high concentrations in some of the most remote sites in the study, including Lake Tahoe in the Sierra Nevada.
“The mechanism of transport of these plastics is not clear, especially when we talk about very small fragments or textile fibres,” said Dr. Nava. “We are wearing a lot of synthetic clothes, the majority of which are made of polyester, and they end up in aquatic systems. Even from far away, there can be atmospheric circulation and patterns that can carry these plastics a long way.”
Forty-five percent of the lakes studied contained more than one plastic particle per cubic metre of water, whilst the most polluted lakes had more than ten particles per cubic metre. The researchers state that concentrations of microplastics in Lakes Lugano and Maggiore at the Swiss-Italian Border and Lake Tahoe in the USA exceed those in ‘floating garbage patch’ oceanic gyres where huge rafts of plastic waste accumulates.
The findings have important implications for drinking water provision. Some of the lakes found to have high plastic concentrations – including Lake Maggiore, Lake Tahoe and Lough Neagh in Northern Ireland – are valuable sources of drinking water.
However, these large lakes often have high water ‘residence times’, meaning that water stays in the system for long periods of time – in Lake Tahoe this can be as high as 650 years. This means that the lakes can act as sinks for plastic pollution which is not flushed out and so accumulates in the system.
This finding presents significant challenges to water managers seeking to provide safe, clean drinking water to communities. It also is a valuable insight for the growing network of freshwater restoration scientists seeking to use nature-based solutions to help improve drinking water quality for humans.
Widespread microplastic pollution also has implications for freshwater ecosystems and even climate change. “Plastic that accumulates on the surface of aquatic systems can promote the release of methane and other greenhouse gases,” explained Dr. Nava. “Plastics can reach beyond the hydrosphere and interact with the atmosphere, biosphere and lithosphere, potentially affecting biogeochemical cycles, including the circulation between the various compartments of the earth of chemical elements that pass from living matter to inorganic matter through chemical transformations and reactions, through mechanisms that have yet to be understood and require a holistic assessment of plastic pollution in lentic [freshwater] systems.”
Microplastic pollution has been emerging as an environmental issue in recent years, as global society produces around 400 million tonnes of plastic waste each year, and plastic fibres have been documented on both the highest mountain ranges and deepest ocean trenches. The study by Dr. Nava and colleagues is valuable in documenting the startling extent of microplastic pollution in lakes and reservoirs.
Moreover, the study – along with another by Dr. Hudson Pinheiro and colleagues about microplastic pollution on coral reefs in the same issue of Nature – contributes to ongoing discussions at the United Nations over a new treaty to eliminate plastic pollution. Talks over a new plastic treaty began in March 2022 and are due to conclude in 2024.
This fast-track timescale offers only a short window for scientists to make their voices heard in negotiations. These studies provide timely documents of the magnitude and extent of global plastic pollution, and reminders of the urgent need to tackle it, both for people and nature.
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This article is supported by the MERLIN project.
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