an “impressive” toxic cocktail found in mountain lakes

This article, originally published in The Conversation, written by Dirk S. Schmeller, professor at the Ecole Nationale Supérieure d’Agronomique de Toulouse, discusses research conducted in lakes in the French Pyrenees. Reprinted under Creative Commons license.

Compared to the plains flooded by humans, the mountains are a paradise. A sanctuary for many tourists, for our dear pets and of course also for our wild animals. Clean air, clean water, green landscapes, impressive reliefs and a lot of tranquility.

However, this paradise is cracked. Climate change has a particularly strong impact on these altitudes (as in the Arctic and Antarctic) and degrades forests. The increase in average temperature is more marked there than on the plain, just as the variations in precipitation – there are sometimes droughts and sometimes floods – which help to make our glaciers disappear. New studies have also shown that plastic pollution has reached mountains believed to be untouched.

Why is this lake affected, and not another? In 2014, we achieved an important breakthrough after three years of careful teamwork: We were able to demonstrate that the zooplankton of mountain lakes constitute a biological barrier that preserves the habitat of amphibians (ponds and mountain lakes). It protects them from the dangerous chytrid fungus Batrachochytrium dendrobatidisthe cause of chytridiomycosis.

However, zooplankton are very sensitive to environmental changes, especially in mountainous areas, which experience extreme environmental conditions and can serve as habitat for relatively few adapted species.

During our research, we were also able to observe some very striking changes: the disappearance of amphibians, growth of algae, ever-increasing variations in water levels, and so on.

In 2016, we launched the Belmont-Forum-funded project “Humans, Pollution and Pathogens”. Purpose: to take a closer look at the development of mountain lakes. In addition to studying the dynamics of zooplankton, bacteria and other microorganisms, the aim was also to better understand the chemical pollution of these waters.

To analyze chemical pollution, we placed passive samplers in eight mountain lakes in the French Pyrenees located between 1714 and 2400 m altitude. Passive samplers, made of silicone pads, simulate fat bodies of live animals and have the function of accumulating lipophilic (fat-loving) substances. Most of the 1,500 chemical molecules of pesticides and other organic substances (which contain many carbon atoms) that are currently circulating in Europe and in the world are precisely lipophilic.

We visited each of our lakes three times a year for three years (2016-2018) to perform not only a spatial but also a temporal analysis of the pollution. In the laboratory, it is today possible to detect 479 organic chemicals, including persistent organic pollutants, polycyclic aromatic hydrocarbons, old and current pesticides, biocides and musk fragrances.

It was clear to us that we needed to find chemicals in our lakes. Why should they be spared when we have already chemically contaminated almost desert areas on our planet, such as Antarctica? However, we were surprised by the extent of this pollution: we discovered 141 different molecules in our eight mountain lakes, in the Ariège Pyrenees (two lakes), Néouvielle (three lakes) and Béarn (three lakes).

Among them, fungicides, herbicides, insecticides, difficult-to-degrade pesticides, polycyclic aromatic hydrocarbons, polychlorinated biphenyls and others. We were able to detect between 31 and 70 different molecules per lake. The greatest diversity of molecules was found in the Ayes dam in Ariège.

An impressive chemical cocktail in the eight lakes that results in chronic toxicity to crustaceans. The latter are an important component of zooplankton, and their abundance decreases as toxicity increases. Our data also show a reduction in the diversity of wheeled animals, another group of zooplankton species, with increasing toxicity to algae.

The latter come mainly from the detected herbicides (eg atrazine, terbuthylazine and others). We assume that some algae are killed by pollution and that the specialized wheeled animals that feed on these algae also disappear locally. This is a hypothesis that needs to be tested further.

The chemical pollution of mountain lakes causes a sharp change in the composition of the zooplankton community and therefore in the functioning of these ecosystems. This may be one of the reasons why algae grow in some of our lakes because the crustaceans, once gone, can no longer control the growth of green algae.

The same could be the case for other pathogens and therefore pose a health risk to humans and grazing livestock. Our samples will be examined further in this direction.

There is still the question of how this pollution arose. The great diversity of molecules is very likely associated with atmospheric transport: the chemicals used in the plain are lifted into the air by evaporation. These air masses are then pushed towards the mountains and the chemicals they contain pour out there in the form of precipitation.

also read : These glacial lakes that threaten the Kingdom of Bhutan

These molecules are then found in mountain lakes and can accumulate in living organisms, for example in introduced fish, and of course in zooplankton. The high toxicity in some of our mountain lakes is mainly caused by two molecules, diazinon and permethrin, very active insecticides. Diazinon is used to fight cockroaches, silverfish, ants and fleas in the home.

Permethrin is found in products to control sucking insects, such as mosquitoes or ticks, and is used to protect dogs and pets. It is also found in insecticides for humans. This means that these two molecules were most likely introduced into the lakes by local sources (such as domestic animals, tourists, dogs) in high concentrations, otherwise we would have struggled to detect them in the hundreds of hectoliters of water found in these lakes.

A radical change of mentality is needed: we must stop using these insecticides. Only the chemicals that we do not use will have no impact on our environment. Self-cleaning of lakes, which is possible through biological processes and through dilution, can only take place if no new pollutants are introduced into the ecosystem. There are already herbal alternatives to insecticides, such as vegetable oil sprays, or repellents such as citronella.

But the question also arises as to who is responsible for the pollution and degradation of mountain lakes: the producers of these products or the users? Decision makers are challenged.


The Axa Research Fund was established in 2007 to accelerate and share scientific knowledge on major societal issues and has supported nearly 650 projects worldwide, led by researchers from 55 countries. To find out more, visit the Axa Research Fund website or follow us on Twitter @AxaResearchFund. Dirk S. Schmeller, Professor of Conservation Biology, Axa Chair for Functional Mountain Ecology at the École Nationale Supérieure Agronomique de Toulouse, University of Toulouse III – Paul Sabatier. This article is republished from The Conversation under a Creative Commons license. Read the original article. © Pixabay

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