UV and tillage abrasion facilitate macro- and micro-plastic fragmentation in agricultural soils

Understanding mulch film fragmentation is essential for predicting macroplastic (MaP) and microplastic (MiP) contamination in farmland. Under laboratory conditions, we investigated the fragmentation of four typical mulch films (8 µm polyethylene (PE) (PE08-f), 40 µm PE (PE40-f), 15 µm polybutylene adipate terephthalate-based film (PBAT-f), and 15 µm starch-based film (Starch-f)) at two soil moisture levels (20% and 60% of field capacity) under UV exposure, tillage abrasion (TA, using a rotavator model), both factors combined (UVTA), and twice UVTA (2UVTA). UV more effectively generated MiPs (590-4800 items 100 cm^-2), whereas TA more effectively generated MaPs (up to 2.3 items 100 cm^-2), if comparing individual factors only. Across all treatments, Fourier transform infrared spectroscopy and scanning electron microscopy revealed that 2UVTA induced the strongest surface oxidation and abrasion, accelerating film mass loss (1.4-18.5%) and promoting MaP (0-3.3 items 100 cm^-2) and MiP (1970-30200 items 100 cm^-2) formation. Most MiPs were fragment (29.2-78.4%) or particle (15.2-69.6%) shaped, predominantly < 500 µm (62.3-97.5%). Starch-f fragmented most, followed by PBAT-f, PE08-f, and PE40-f. Redundancy analysis showed strong positive correlations between 2UVTA and MaP area distribution (%), MaP and MiP counts. Our results demonstrate that UV and TA, together with soil moisture, drive distinct fragmentation behaviors in PE versus biodegradable films. Further study is urgently needed to take agricultural management practices into account for better understanding plastic fragmentation and its potential risks to soil health.