Exploration of Source-Specific Markers for Secondary Microplastics Derived from Polyolefin-Coated Fertilizers

Polyolefin-coated fertilizers, widely used in Japanese agriculture, were analyzed to identify characteristic additives that could serve as source-specific markers for secondary microplastic originating from them. Four types of polyolefin-based samples were examined, revealing polyethylene as the main polymer component, along with poly(vinyl acetate), starch, and clay minerals as minor components. Thermal desorption gas chromatography-mass spectrometry led to the identification of three plasticizers, three fatty acids, and levoglucosan, a thermal degradation product of starch. Among these compounds, characteristic fatty acids and levoglucosan were found not only in unused commercial products but also in environmental samples and laboratory-degraded materials exposed to heat and ultraviolet radiation. These findings demonstrate their utility as markers of fertilizer-derived microplastics. Based on these findings, a stepwise identification framework was constructed and applied to white secondary microplastics collected from agricultural soil, with the origin of 14 out of 15 microplastic samples being attributed to polyolefin-coated fertilizers. Thus, we present a practical framework for source attribution of microplastics in agroecosystems.