River–Groundwater Interaction and Recharge Effects on Microplastics Contamination of Groundwater in Confined Alluvial Aquifers

Abstract

Literature provides only a few examples of contamination of groundwater with microplastics, mainly investigated using a chemical approach. Little importance is given to the hydrogeological processes able to affect the contamination, such as river–groundwater interactions. This study was carried out with two aims. The first aim is the formulation of a method with a high result-to-cost ratio, based on the hydrogeological aspects of the investigated area. Microplastics were extracted from samples through filtration and successively counted and characterized morphologically through analysis of optical microscopy images. The second aim is to evaluate the presence of microplastics in some portions of an alluvial aquifer using this methodology. Microplastics in groundwater showed a higher circularity and Feret diameter than those found in surface waters, indicating that in porous aquifers the transport is likely more influenced by the microplastics’ shape than by their size. The aquifer recharge did not modify the microplastics’ characteristics in groundwater, whereas in surface water the flood wave promoted the resuspension of microplastics with lower circularity. These findings provide new pieces of evidence on the presence and transport of microplastics in both groundwater and surface waters, underlining how the hydrogeological characteristics of the area can be one of the main drivers of microplastics’ contamination.

High-throughput microplastic assessment using polarization holographic imaging

“…Circularity measures how closely a shape resembles a perfect circle, which has a circularity value of 1, whereas a highly elongated object approaches a value of 0. The circularity of MPs reflects their interaction with the environment 53 .…”

Microplastics in Groundwater: Pathways, Occurrence, and Monitoring Challenges

“…They may be taken up by benthic organisms or transported through the hyporheic zone (HZ) into the GW [54]. This process depends on the relationships between pore diameters and MPs' dimensions [55], particularly in the case of MPs of smaller diameters. Smaller size MPs can move through the pore space from the surface of the streambed into the subsurface layers [48,56].…”

Contaminant Trends in Urban Groundwater: Case Study from Ljubljana (Central Slovenia)

“…Numerous EOCs are frequently detected at high concentrations across Europe [63] but are not yet formally regulated by European directives, despite their potentially harmful effects on the environment and human health [64,65]. Among the emerging pollutants, microplastics have recently gained attention due to their ubiquity and persistence in the environment, especially as their occurrence, fate and transport processes in groundwater are not yet fully understood [66][67][68][69]. The main obstacle to achieving comparable results in existing reports on the significance and distribution of microplastics and other emerging pollutants in natural waters (e.g., perfluorinated compounds, benzotriazoles and certain widely used pharmaceuticals) lies primarily in the challenges of sampling and analytical methods.…”