Anthropogenic Mercury Discovered At The Bottom Of The Mariana Trench
Ecologists from France and China collected soil and water samples from the bottom of the Mariana trench and found large amounts of methylated mercury, a toxic compound that can only be produced by human civilization. They told about this at the Goldschmidt 2020 scientific conference.
"This discovery was a big surprise. In the past, we assumed that methylated mercury occurs only in the upper layers of the ocean. Therefore, it was believed that deep-sea fish species were protected from the accumulation of these toxins. It turned out that this is not the case, " said one of the authors of the study, an ecologist from Tianjin University (China) Ruoyu Sun.
Mercury and its compounds are very harmful to humans and other living creatures. According to ecologists today, it is especially dangerous for animals that are located at the upper levels of the food chain, in the liver, and other organs of which it accumulates quite quickly. Therefore, mercury contamination of nature is especially dangerous for representatives of the indigenous peoples of the North, who eat the meat of seals, polar bears, and other large animals.
Early observations of the spread of mercury have shown that it can accumulate in different ecosystems, either in its pure form or as mercury oxide or its combination with methane. Pure mercury is very mobile, but it is chemically inactive. In this case, methylated mercury, the mechanism of formation of which is still unknown, on the contrary, actively interacts with various biomolecules and easily penetrates the body of fish and animals.
Deep-sea traces of humanity
Sun and his colleagues found that similar traces of human civilization began to occur even in the deepest layers of the World's oceans. Researchers studied water and soil samples collected at the bottom of the Mariana trench four and three years ago. Scientists got them using the deep Sea Warrior bathyscaphe, which can descend to a depth of 10 thousand meters.
During a series of dives into the Mariana trench, Sun and his colleagues collected samples of soil, water, and deep-sea crustaceans that live at depths of 5.5 to 9.2 thousand meters. Studying the contents of these samples, scientists measured the concentration of mercury compounds, as well as analyzed the ratio of its isotopes in the body of marine fauna and in the ground.
To the great surprise of ecologists, they found a lot of mercury everywhere, and the ratio of even and odd isotopes of mercury in them was exactly the same as in toxic molecules from the body tissues of fish, shellfish and other inhabitants of the near-surface layer of the seas, in which methylated mercury accumulates.
Sun and his colleagues believe that from the upper layers of the Pacific ocean, this compound gradually penetrates to its bottom and quickly accumulates there. According to ecologists, scientists greatly underestimate how human activity affects the spread of toxic mercury compounds across the planet. This should be taken into account when assessing the consequences of such pollution.