Microplastic in Danish Soils—Combining Extraction and Infrared Spectroscopy Prediction Methods

ABSTRACT Microplastic (MP) pollution presents a considerable challenge to soil ecosystems, yet the local‐scale presence and concentration of MP in soils remain poorly understood. This is partly because traditional extraction methods are time‐consuming, and MP concentrations vary widely due to factors such as local exposure levels and soil properties. In this study, the effectiveness of a density separation method as well as visible near‐infrared spectroscopy (vis–NIRS) and Fourier‐transform infrared (FTIR) spectroscopy for quantifying MP concentrations were assessed. Eight different soils artificially polluted by MP in concentration levels from 0.2 to 20.0 g MP kg −1 were analyzed. Additionally, this study investigated the distribution of MP in various ecosystems around Viborg, Denmark. The results showed that the more time‐consuming density separation method effectively extracted MP, showing strong correlations between spiked and extracted concentrations ( r > 0.96), although the extraction accuracy varied by MP type and soil properties. Soils with non‐complexed organic carbon (NCOC) showed greater interference in MP extraction, particularly for polypropylene, polyethylene, and polyamide. The faster spectroscopic analyses using vis–NIRS and FTIR effectively predicted MP concentrations, with vis–NIRS showing a moderate predictive accuracy ( R 2 = 0.663), similar to FTIR ( R 2 = 0.622). These results highlight the potential of spectral methods for rapid MP quantification. However, further work is needed before vis–NIRS or FTIR scans can be reliably used to estimate MP concentrations, such as the development of a spectral library for MP in soils to account for varying MP types, colors, and soil properties.