Bottom sediments of a spring watercourse as a filter for microplastic – on the example of the Młynówka in Stary Imielnik (municipality of Stryków) – preliminary studies

Microplastic (MP) are currently one of the most serious and emerging environmental problems that involve rivers and streams with particular clarity. In the present study of the spring-fed watercourse bed sediments, the presence of microplastic particles was demonstrated and the pathway of their penetration into this environment was identified. The presence of microplastic in the form of fine plastic particles, taking the shape of fibres and fragments in dark and light colours within the hyporheic zone was found. This occurs directly beneath the lowland watercourses with sandy bottoms. There, groundwater is in contact with surface water and mixing takes place. This is an important ecological zone, where chemical and physical processes are crucial to the river environment. In the hyporheic zone there is an exchange of nutrients and oxygen between river water and groundwater, which is crucial to the ecological health of the river and its surroundings. This zone can play an important role in the processes of microplastic transport and retention, as it is where microplastic is washed into the channel infiltration (downwelling) zones and sediment is deposited on the sand filter penetrated by the mixture of river water and groundwater.