2023-09-17 15:00:10
A “Tetragnatha” spider. ALAMY STOCK PHOTO
Mercury is a terrible poison. A “global pollutant”, say scientists, because they are found everywhere on the globe. Fearsome because it takes a tortuous path: present on land, it reaches its full toxicity when it is transformed in water by aquatic bacteria into methylmercury. It then accumulates in all the creatures found there, from insects to fish. For humans, it can be harmful, particularly for fetuses. So much so that the World Health Organization has classified it among the ten pollutants of greatest concern. Because, even if its use has been considerably reduced, gold panning, the consumption of fossil fuels, particularly coal, and even old industrial waste continue to pollute waterways, lakes and oceans. The European Environment Agency estimates that the concentration of mercury in the seas is three times higher than it should be. And it’s worse in some lakes.
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Spiders of the genus Tetragnatha are at the forefront of this sad spectacle. They even play a role, for the moment secondary, but which could gain momentum, according to an article published Wednesday September 13 in the journal Environmental Science & Technology Letters. Scientists from the US Geological Survey (USGS) point out: these creatures feed exclusively on aquatic insects and are devoured by frogs, snakes and birds. They therefore help to reinject the pollutant into the terrestrial food chain.
So should we get rid of it? ” Surely not, protests Sarah Janssen, first author of the publication. Otters and rats Muskies also feed in water. Tadpoles grow in rivers and then, becoming frogs, emerge. Aquatic insects breed on land. They also contribute to the transfer. » Understand: we are not going to eradicate them all.
True sentinels
Especially since tetragnaths have an advantage: they are real sentinels. They see everything, preserve everything. Indeed, the different sources of mercury (natural, combustion, waste) each present a particular balance between the different isotopes. By analyzing insects, fish and spiders in two tributaries of North America’s immense Lake Superior, USGS researchers showed, for the first time, that the latter retained the signature already observed in the first two.
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And, between the dragonfly, the perch and the spider, there is no comparison, scientists insist. First of all, the spider not only provides information on aquatic pollution, it also shows how mercury is transferred to the terrestrial environment. But that’s not all, insists David Walters, research coordinator. “They are much easier to catch, no need for equipment other than a flashlight, he said. Much more fixed too, unlike fish which never stop moving; they therefore offer incomparable spatial information. Finally, tetragnaths are found almost everywhere where there is fresh water: they will therefore allow global comparisons. »
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