Field Lysimeter Experiments for Tracing Microplastics Transport in the Unsaturated Zone

Understanding the transport of microplastics (MPs) in the unsaturated zone (UZ) is essential for assessing their environmental impact, particularly regarding groundwater contamination. MPs are increasingly detected in groundwater systems; however, their transport mechanisms through the UZ remain poorly understood, and field-scale experimental evidence is scarce.

This study presents a field-based methodological approach using lysimeter experiments to investigate MP migration under realistic environmental conditions. Four lysimeters, each designed as a vertical column with a diameter of 0.6 metres, were installed outdoors to closely simulate natural UZ environments. The columns were packed with 16 cm of sand and gravel of known granulometric fractions, incorporating variable grain sizes to represent diverse porous media and hydraulic properties. Comprehensive granulometric analyses and infiltration tests were conducted to characterise the physical properties of the columns. Commercial Polypropylene (PP) MPs of different shapes (fibres, fragments, and spheres) were applied as tracers, alongside deuterium oxide (D₂O) as a conservative tracer for hydraulic characterisation.

This experimental approach provides valuable data on MP transport under controlled yet realistic conditions, reducing uncertainties associated with laboratory-only studies. The experimental design allows for the quantification of retention and breakthrough behaviour of MPs under variable hydraulic regimes. Furthermore, the integration of multiple tracer shape-types facilitates the differentiation between physical transport processes, providing a robust framework for future modelling efforts.  

A comprehensive description of the experimental setup, together with the initial results derived from the lysimeter studies, will be presented.

 

This research is part of the project “Improved methods for determination of transport processes and origin of microplastics in groundwater resources—(GWMicroPlast)” (J1-50030), funded by the Slovenian Research and Innovation Agency (ARIS).