Astner A F, Hayes D G, O'Neill H, Evans B R, Pingali S V, Urban V S, Schaeffer S M, Young T M
The University of Tennessee, Biosystems Engineering and Soil Science, 2506 E J. Chapman Dr, Knoxville, TN 37996, United States of America.
The University of Tennessee, Biosystems Engineering and Soil Science, 2506 E J. Chapman Dr, Knoxville, TN 37996, United States of America.
Sci Total Environ. 2023 Apr 20;870:161867. doi: 10.1016/j.scitotenv.2023.161867. Epub 2023 Jan 28.
Microplastics (MPs) and nanoplastics (NPs) from mulch films and other plastic materials employed in vegetable and small fruit production pose a major threat to agricultural ecosystems. For conducting controlled studies on MPs' and NPs' (MNPs') ecotoxicity to soil organisms and plants and fate and transport in soil, surrogate MNPs are required that mimic MNPs that form in agricultural fields. We have developed a procedure to prepare MPs from plastic films or pellets using mechanical milling and sieving, and conversion of the resultant MPs into NPs through wet grinding, both steps of which mimic the degradation and fragmentation of plastics in nature. The major goal of this study was to determine if cryogenic exposure of two biodegradable mulch films effectively mimics the embrittlement caused by environmental weathering in terms of the dimensional, thermal, chemical, and biodegradability properties of the formed MNPs. We found differences in size, surface charge, thermal and chemical properties, and biodegradability in soil between MNPs prepared from cryogenically treated vs. environmentally weathered films, related to the photochemical reactions occurring in the environment that were not mimicked by cryogenic treatment, such as depolymerization and cross-link formation. We also investigated the size reduction process for NPs and found that the size distribution was bimodal, with populations centered at 50 nm and 150-300 nm, and as the size reduction process progressed, the former subpopulation's proportion increased. The biodegradability of MPs in soil was greater than for NPs, a counter-intuitive trend since greater surface area exposure for NPs would increase biodegradability. The result isassociated with differences in surface and chemical properties and to minor components that are readily leached out during the formation of NPs. In summary, the use of weathered plastics as feedstock would likely produce MNPs that are more realistic than cryogenically-treated unweathered films for use in experimental studies.
来自蔬菜和小水果生产中使用的地膜及其他塑料材料的微塑料（MPs）和纳米塑料（NPs）对农业生态系统构成重大威胁。为了对MPs和NPs（微纳塑料，MNPs）对土壤生物和植物的生态毒性以及在土壤中的归宿和迁移进行对照研究，需要能够模拟在农业田地中形成的MNPs的替代微纳塑料。我们开发了一种程序，通过机械研磨和筛分从塑料薄膜或颗粒制备MPs，并通过湿磨将所得MPs转化为NPs，这两个步骤都模拟了自然界中塑料的降解和破碎。本研究的主要目标是确定对两种可生物降解地膜进行低温处理，在形成的MNPs的尺寸、热学、化学和生物降解性特性方面，是否能有效模拟环境风化引起的脆化。我们发现，由低温处理薄膜与环境风化薄膜制备的MNPs在土壤中的尺寸、表面电荷、热学和化学性质以及生物降解性存在差异，这与低温处理未模拟的环境中发生的光化学反应有关，如解聚和交联形成。我们还研究了NPs的尺寸减小过程，发现尺寸分布是双峰的，群体集中在50nm和150 - 300nm，随着尺寸减小过程的进行，前一个亚群体的比例增加。MPs在土壤中的生物降解性大于NPs，这是一个违反直觉的趋势，因为NPs更大的表面积暴露会增加生物降解性。该结果与表面和化学性质的差异以及在NPs形成过程中容易浸出的次要成分有关。总之，使用风化塑料作为原料可能会产生比用于实验研究的低温处理未风化薄膜更符合实际的MNPs。
