Agricultural mulch films as soil microplastic contamination factor

Abstract

Plastic mulch films are increasingly used in agriculture to improve yields and simplify harvest as well as work processes. Beside the agronomic advantages, the use of mulch films is also associated with the risk of (micro) plastics entering the soil system. To which extend weathering and fragmentation of mulch films potentially leads to a soil contamination depends on the plastic characteristics, e.g. in terms of thickness, colour and UV resistance, which is associated with different purposes of mulch film application. This study aims to analyse the changes in plastic film properties as basis for plastic fragmentation and finally microplastic contamination, resulting from photodegradation and mechanical stress. We used different plastic mulch films and applied fixed UV light intensities at 50ºC temperature. We applied varying time of UV exposure and performed an abrasion test, where plastic film and soil were mixed at 4 rpm for 2 months to simulate mechanical stress. After the different treatments the effects on chemical groups, surface characteristics, hydrophobicity and mechanical stability of the mulch films were analysed. Therefore, the following techniques were utilized: (i) Fourier transform infrared with attenuated total reflectance (FTIR-ATR) spectroscopy, (ii) 3d laser confocal scanner microscopy (LSM), (iii) optical contact angle (OCA) analysis, and (iv) universal nanomechanical testing (UNAT). The FTIR-ATR analysis revealed spectral changes indicating an alteration in the carbonyl group content, related to photodegradation, when compared with samples without UV treatment. The OCA also demonstrated variations in the wettability of samples in both treatments, caused by the variation on the carbonyl content. Mechanical stress treatment also highlights changes on the sample surface, e.g., new scratches on the sample surface. UNAT results indicate variation on the Young’s modulus, related to the samples crystallinity. Overall, the combination of analyses suggests that photodegradation and mechanical stress cause changes in the carbonyl content, which can influence wettability and mechanical stability. Together with the surface changes under mechanical stress, the study presents a potential pathway of mulch foil fragmentation and MP formation.