A “Tetragnatha” spider. ALAMY STOCK PHOTO
Mercury is a terrible poison. A “global pollutant,” scientists say, because it occurs all over the world. Frightening because it takes a tortuous path: present on land, it reaches its full toxicity when it is converted into methylmercury by aquatic bacteria in the water. It then accumulates in all living creatures found there, from insects to fish. It can be harmful to humans, especially fetuses. So much so that the World Health Organization lists it among the ten pollutants of greatest concern. Even though use has been significantly reduced, gold panning, the consumption of fossil fuels, especially coal, and old industrial waste continue to pollute waterways, lakes and seas. The European Environment Agency estimates that mercury levels in the oceans are three times higher than they should be. And in some lakes it’s even worse.
Also read (2017): Article reserved for our subscribers. Pollution: French pregnant women are excessively exposed to arsenic and mercury
Spiders of the genus Tetragnatha are the focus of this sad spectacle. They even play a role that is secondary at the moment but could be increasing, according to an article published Wednesday, Sept. 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 eaten by frogs, snakes and birds. They thus help to reintroduce the pollutant into the terrestrial food chain.
So should we get rid of it? “Certainly not,” protests Sarah Janssen, first author of the publication. Otters and rats Musk deer also feed on water. Tadpoles grow in rivers and then hatch into frogs. Aquatic insects breed on land. They also contribute to the transfer. » Understand: We will not eradicate them all.
True Guardians
Especially since tetragnaths have one advantage: they are real guardians. They see everything, preserve everything. In fact, the different sources of mercury (natural, combustion, waste) each have a particular balance between the different isotopes. By analyzing insects, fish and spiders in two tributaries of the vast Lake Superior in North America, USGS researchers showed for the first time that the latter retain the signature already observed in the first two.
Also read: Mercury pollution would cause Europe to lose intelligence and money
And there is no comparison between the dragonfly, the perch and the spider, scientists emphasize. First of all, the spider not only provides information about water pollution, it also shows how mercury enters the terrestrial environment. But that’s not all, emphasizes David Walters, research coordinator. “They’re much easier to catch, you don’t need any equipment other than a flashlight,” he said. They are also much more rigid, unlike fish that never stop moving. They therefore offer unparalleled spatial information. After all, tetragnaths occur almost everywhere there is fresh water: they therefore enable global comparisons. »
You still have 18.3% of this article left to read. The rest is reserved for subscribers.