Application of FTIR-ATR spectroscopy in the detection of microplastics in Croatian agricultural soils

Microplastics (MP) smaller than 5 mm have become widespread in the environment, including agricultural soils, due to increasing production and use. MP is characterized by a large specific surface area and hydrophobicity, which makes it a carrier of organic pollutants, heavy metals, and microorganisms. Their slow degradation and small size allow it to enter the food chain, potentially threatening human health.

Fourier transform infrared spectroscopy coupled with attenuated total reflectance (FTIR-ATR) is a powerful, cost-effective, and non-destructive method for identifying MP, and analyzing its functional groups in soil samples. This study aimed to assess the applicability of FTIR-ATR spectroscopy for detecting MP in Croatian Luvisol and Eugley soils. Polyethylene (PE) and polypropylene (PP) were added to soils at concentrations of 2% and 5% and analysed in triplicate.

FTIR-ATR successfully detected PP and PE functional groups in both soils. However, in Eugley soil, strong absorption bands from minerals and inorganic soil particles overlapped the characteristic PP bands at 1454 cm⁻¹ and the 1237–720 cm⁻¹ range, whereas in Luvisol, interference occurred only within the 1237–720 cm⁻¹ range. These findings highlight FTIR-ATR strong potential for MP detection in soils, although further research is needed for MP particle quantification.

Keywords: microplastics, polyethylene, polypropylene, FTIR-ATR spectroscopy, agricultural soil