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The influence of microplastics on the dry end of the soil-water retention curve

2023
Hannes Laermanns, Markus Rolf, Susanne Forche, Elena Castrucci, Alexander Stelzer, Christina Bogner

Summary

Researchers measured how adding microplastics to soil affects the soil-water retention curve beyond the wilting point — the level at which plants can no longer extract water. Different microplastic types affected water retention differently depending on their surface properties and shape. These changes in soil water dynamics could affect plant available water and agricultural productivity in microplastic-contaminated soils.

Polymers

Most studies focus on the detection of microplastic particles in different compartments of the environment. While impacts of microplastics on aquatic systems have already a wide acceptance in public, the research on microplastics in terrestrial systems is quite young. Our study aims to decipher the consequences of microplastics on the soil-water retention curve beyond the wilting point. Using a dew point WP4C hygrometer, we measured water retention curves of loess and sand samples with added microplastics, namely amorphous biopolymer, polystyrene in two sizes and three different types of UV-aged particles. All the different microplastics were added in concentrations of 0.1 wt.%, 0.5 wt.%, and 4.5 mg/kg. Reference samples without microplastics were prepared as well. For the analysis, we fitted the Webb model and calculated the water content at the wilting point and the slope of the soil-water retention curve. Our preliminary results did not show any significant differences between the different microplastics and their concentrations, however, the lowest slope and highest water content at pF 4.2 were observed in the samples without microplastics. Furthermore, the results indicated a greater variability with increasing size of microplastic particles.

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