Microplastic Lateral Transport in Agricultural Slopes: A Field-Based Approach

Microplastics (MPs, diameter < 5mm) are pervasive, persistent environmental contaminants. MPs enter agricultural soil via direct sources, such as plastic mulches and irrigation pipes, as well as indirect sources, including compost and sewage sludge. Once in soil, MPs can be incorporated into soil aggregates, altering soil structure and hydro-physical properties (e.g., bulk density, aggregate stability, water retention curve). These changes could potentially limit or enhance the transport of MPs in soil as well as their detachment and transport with runoff and erosion. Despite their significance, research on MPs transport on agricultural fields via runoff and erosion remains limited, and detailed empirical data is missing. 

This study aims to investigate the dynamics of MPs transport on agricultural slopes during natural rainfall events, focusing on quantifying lateral MPs transport with runoff and erosion, assessing MPs enrichment or depletion in eroded sediment, exploring the preferential flow patterns of MPs (whether free or sediment-bound), and comparing transport behaviors of various MPs polymer types. To achieve this, we will construct three enclosed soil flumes (22 m long and 2 m wide) in hilly south-Limburg, the Netherlands. From April to October 2025, we will use ISCO automatic samplers, attached at the outlet of the soil flumes, to capture runoff and eroded sediment at six-minute intervals. For each rainfall event, the runoff and eroded sediment will be continuously collected and quantified. Additionally, MPs in runoff water and eroded sediment will be extracted and analyzed respectively using μ-FTIR to determine the MPs polymer types and particle numbers.  

This project is currently in the initial stages, and we anticipate installing the soil flumes in April 2025, followed by collecting and analyzing the data as described, with results expected to be available at the beginning of 2026. The expected findings aim to bridge the gap in empirical data regarding MPs' lateral transport in agricultural slopes during natural rainfall events. We will use this dataset to incorporate MPs as a pollutant in erosion models, enabling the estimation of their transport under various scenarios. The project will also provide insights into the potential for agricultural soils to act as sources or sinks of MPs pollution.