Emission of microplastics by geosynthetics during Snow Farming

Geosynthetics are a wide range of materials used in many fields ranging from civil engineering to agriculture, road transport and environmental protection. Made up of synthetic or natural polymers, these materials are characterized by their strip shape of varying width and length. It is estimated that currently 150 million m² of geosynthetics are used in France (data from the French Geosynthetics Committee). Despite this massive and constantly increasing use in recent years, their impact on the environment and in particular in terms of the emission of plastic particles, has been very little studied. It is therefore crucial (1) to quantify the risk of fragmentation and emission of plastic particles by geosynthetics and (2) to investigate how exposure to environmental conditions or implementation methods of these materials are likely to modify the quantities of particles emitted.In partnership with the Tignes ski slopes authority, the Grande Motte cable car company and the Cimes Conseil design office, a quantification of the fluxes of plastic particles emitted by geosynthetics used for Snow Farming was set up between 2020 and 2023. In a context of climate change, Snow Farming makes it possible to reduce the melting of snow on sensitive parts of the ski area (e.g. ski lifts), during summer periods and thus to optimize the opening periods of the ski stations. The geosynthetics used in this context are exposed to extreme environmental conditions including strong ultraviolet radiation and significant daily temperature variations. These conditions could lead to the fragmentation of plastics and to the subsequent release of microplastics.The work carried out in this study focused on vertical (through the snow cover) and horizontal (at the surface) particle fluxes. These fluxes were compared to the atmospheric fallout of microplastic at the scale of the glacier on which the ski area is located. In addition, 3 types of geosynthetics were compared: a waterproof PVC tarpaulin, a permeable polypropylene tarpaulin and a tarpaulin made from natural materials. The work showed very contrasting results between the 3 types of tarpaulins.Permeable polypropylene tarps showed the greatest fluxes of particles (microplastics and mesoplastics) to the snowpack in terms of mass, with transfers exceeding one meter in depth. PVC tarpaulins showed grater fluxes in terms of number of particles and the transfers were limited to snow directly in contact with the tarpaulins. These differences are probably explained by contrasting emissions processes linked either to environmental exposures or to the handling of the tarpaulins. No plastic contamination could be detected in the tarpaulins of natural origin. On the scale of the glacier, the fluxes emitted annually represent approximately 2.3 kg and are of the same order of magnitude as the atmospheric fallout (about 8 kg) while the tarpaulins only cover 0.44% of the glacier surface.