Microplastics in groundwater: a global analysis

Microplastic particles (MPs) have emerged as contaminants of concern in the aquatic environment and recent research has made substantial progress to improving our understanding of the transport of MPs in riverine systems. Much less is known about the potential contamination with MPs of the world's groundwater resources while transport into and fate in these anoxic systems is largely unclear. However, closing this knowledge gap is imperative to predict any potential long-term impact of MPs on groundwater ecosystems. Here we present first results of a global groundwater sampling study conducted with the help of the scientific community. Samples were obtained from around the world via caves, boreholes, monitoring wells and surface springs. Sample collection followed a standardised protocol to guarantee comparability among different sampling locations and to ensure ease of use at low cost. At each site, about 300 L of groundwater were collected and filtered through a series of metal sieves (123 and 25 µm mesh size). Filtrates and meshes were then stored in 50 mL glass vials for further analysis. Field blanks ¿25 µm were collected on a metal mesh during groundwater sampling to account for potential contamination. Samples were processed by first cutting the metal meshes into pieces and submerging them in a ZnCl2 solution in glass beakers in an ultrasonic bath. Afterwards, mesh pieces were rinsed with ZnCl2 and beaker contents were washed into glass units (270 mL volume) to facilitate density separation. After density separation had completed, the supernatant containing putative MPs was subjected to organic matter digestion using hydrogen peroxide. Samples were then prepared for fluorescent microscopy using Nile red dye, while MP characterisation and polymer identification were carried out using Raman spectroscopy. First results indicate variable MP concentrations in groundwater resources, with increasing concentrations towards the smaller size range. Also see: https://micro2024.sciencesconf.org/559353/document