Novel methodology to form micro- and nano-plastics from agricultural plastic materials and their dimensional, thermal and chemical characterization
Astner, A. F., D. G. Hayes, H. M. O'Neill, B. R. Evans, S. V. Pingali, V. S. Urban, and T. M. Young.  2019.  Science of the Total Environment, 685: 1097-1106.

Abstract:
Release of microplastics (MPs) and nanoplastics (NPs) into agricultural fields is of great concern due to their reported ecotoxicity to organisms that provide beneficial service to the soil such as earthworms, and the potential ability ofMPs and NPs to enter the food chain. Most fundamental studies of the fate and transport of plastic particulates in terrestrial environments employ idealized M Pmaterials as models, such as monodisperse polystyrene spheres. In contrast, plastics that reside in agricultural soils consist of polydisperse fragments resulting from degraded films employed in agriculture. There exists a need for more representative materials in fundamental studiesof the fate, transport, and ecotoxicity of MPs and NPs in soil ecosystems. The objective of this study was therefore to develop a procedure to produceMPs and NPs from agricultural plastics (a mulch film prepared biodegradablepolymer polybutyrate adipate-co-terephthalate (PBAT) and low-density PE [LDPE]), and to characterize the resultant materials. Soaking of PBAT films under cryogenic conditions promoted embrittlement, similar to what occurs through environmental weathering. LDPE and cryogenically-treated PBAT underwent mechanical milling followed by sieve fractionation intoMP fractions of 840 μm, 250 μm, 106 μm, and 45 μm. The 106 μm fractionwas subjected to wet grinding to produce NPs of average particle size 366.0 nm and 389.4 nm for PBAT andLDPE, respectively. A two-parameter Weibull model described the MPs' particle size distributions, while NPs possessed bimodal distributions. Size reduction did not produce any changes in the chemical properties of the plastics, except for slight depolymerization and an increase of crystallinity resulting from cryogenic treatment. This study suggests that MPs formfromcutting and high-impact mechanical degradation as would occur during the tillage into soil, and that NPs form from the MP fragments in regions of relative weakness that possess lower molecular weight polymers and crystallinity.