The participants of the consortium "Microplastics in the Environment" (Tomsk State University, Irkutsk State University and the Institute of Geography of the Siberian Branch of the Russian Academy of Sciences) have completed the first ever large—scale comprehensive study of the cleanest lake on the planet, Lake Baikal, for microplastic pollution. Scientists have found that the majority of synthetic particles are confined to the lower edge of the ice, where the larvae of the Baikal epicura, the famous filter crustacean, hibernate, which largely determines the purity of the lake's waters.
Until recently, the study of microplastics in Lake Baikal was fragmentary. Basically, the water from the surface was studied in the summer, which gave an idea only of the "tip of the iceberg". To get an overall picture of the pollution, the authors conducted a comprehensive interdisciplinary study of the Baikal Bay of Bolshye Koty.
"This place is unique in that, despite the absence of highways, it is stressed by water transport and tourism," explained Julia Frank, one of the authors of the article, director of the TSU Microplastics Research Center in the Environment.
The scientists tested surface waters, water column, bottom sediments, macrophytes, macroinvertebrates and fish, as well as ice and snow in winter for microplastics. The analysis results showed that high concentrations of microplastic particles are observed in certain locations. In some cases, this was due to the properties or characteristics of these locations, for example, at the water's edge, while in others it was due to local pollution (areas of piers and ship parking lots).
Among the polymer particles, scientists have identified both common types — polypropylene, polyethylene terephthalate, polystyrene, polyethylene, polyvinyl chloride, and rare ones — polyvinyl alcohol and alkyd resins — the main component of modern marine paints.
"The study showed that ice and snow work as giant pollution concentrators. Snow collects plastic dust brought by the wind, and ice literally "freezes" particles from the water. The highest concentration of microplastic particles is found at the bottom edge of the ice. It turned out that it was here, on the border of frozen water, that the microplastic content was higher than in open water. Near this layer, significant concentrations of nauplia (larvae) of the famous crustacean Epischura baikalensis, the main filter of Lake Baikal, are observed in winter," said Dmitry Karnaukhov, another participant in the study, a researcher at the IGU Laboratory of General Hydrobiology.
Scientists have found that aquatic plants play an important role in the accumulation of microplastics. Microplastic "sticks" to macrophytes, especially those species that have mucous membranes. Gastropods and amphipod crustaceans, eating these plants, can unwittingly absorb synthetic particles. Fish at the top of the food pyramid accumulate particles eaten by their victims.
According to the authors, the potential danger from the point of view of ecotoxicology is the period of spring ice melting. All the plastic accumulated in the snow and ice during the long Siberian winter simultaneously enters the surface water layer in spring. This "salvo release" occurs just at the moment when life in Lake Baikal is awakening and the larvae of fish and crustaceans begin to actively feed.
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