我们使用机械铣削,研磨和成像分析的逐步过程来展示微塑料和纳米塑料(分别为MP和NP)的形成和尺寸表征。
分散在农业生态系统中的微塑料(MP)和纳米塑料(NPs)可能对土壤和附近水道中的生物群构成严重威胁。此外,NPs吸附的农药等化学物质会损害土壤生物,并可能进入食物链。在这种情况下,农业上使用的塑料,如塑料地膜,对农业生态系统中的塑料污染有重大影响。然而,大多数关于命运和生态毒性的基础研究都使用理想化且代表性较差的MP材料,例如聚苯乙烯微球。
因此,如本文所述,我们开发了一种实验室规模的多步骤程序,以机械方式形成具有代表性的MP和NP进行此类研究。该塑料材料由市售的聚丁酸己二酸酯-共对苯二甲酸酯(PBAT)塑料地膜制备,该薄膜通过低温处理(CRYO)或环境风化(W)脆化,并由未经处理的PBAT颗粒制成。然后通过机械研磨处理塑料材料,形成尺寸为46-840μm的MP,模仿风和机械对塑料碎片的磨损。然后将国会议员筛分成几个尺寸部分,以便进行进一步分析。最后,对106 μm筛分进行湿法研磨,生成20-900 nm的NPs,该过程模仿了地面MP的缓慢尺寸减小过程。通过立体显微仪的图像分析确定了MP的尺寸和形状,并采用动态光散射(DLS)来评估NP的粒度,通过该过程形成的MP和NP具有不规则的形状,这与从农田中回收的MP的几何特性一致。总体而言,这种尺寸减小方法被证明对于形成由可生物降解塑料组成的MP和NP是有效的,例如聚己二酸丁二醇酯 – 共对苯二甲酸丁二醇酯(PBAT),代表用于农业特种作物生产的覆盖材料。
近几十年来,全球塑料产量迅速增加,处置不当,塑料废物缺乏回收利用,导致环境污染,影响了海洋和陆地生态系统1,2,3。塑料材料对于当代农业至关重要,特别是种植蔬菜,小水果和其他特种作物。它们用作地膜、高低隧道覆盖物、滴灌带和其他应用,旨在提高作物产量和质量,降低生产成本,并促进可持续耕作方法4,5。然而,“塑料栽培”的不断扩大引起了人们对农业环境中塑料碎片的形成,分布和保留的担忧。在使用寿命期间通过环境退化引起的脆化过程之后,较大的塑料碎片形成微塑料和纳米塑料(MNPs),这些塑料碎片在土壤中持续存在 或通过水径 流和风迁移到相邻的水道6,7,8。环境因素,如通过阳光的紫外线(UV)辐射,水的机械力和生物因素触发环境分散塑料的塑料脆化,导致较大的塑料碎片分解成宏观或中胚层塑料颗粒9,10。进一步碎片化形成微塑料(MP)和纳米塑料(NPs),反映平均尺寸(公称直径; dp)分别为1-5000μm和1-1000nm11.然而,NPs的 dp 上限(即MP的下限)并未得到普遍同意,在几篇论文中,这被列为100 nm12。
来自塑料废物的MNP对土壤健康和生态系统服务构成了新的全球威胁。与周围环境相比,国会议员从淡水中吸附重金属导致重金属浓度高出800倍13.此外,水生生态系统中的议员通过改变光渗透,导致氧气耗尽,并导致粘附在各种生物群中,包括渗透和积累在水生生物中,造成多种压力源和污染物14.
最近的研究表明,MNPs可以影响土壤地球化学和生物群系,包括微生物群落和植物15,16,17。此外,NPs威胁到食物网17,18,19,20。由于MNP很容易在土壤中经历垂直和水平运输,它们可以将吸收的污染物(如杀虫剂,增塑剂和微生物)通过土壤带入地下水或水生生态系统,如河流和溪流21,22,23,24。传统的农用塑料,如地膜,由聚乙烯制成,使用后必须从田间取出,并在垃圾填埋场中处理。然而,不完全的去除导致大量的塑料碎片在土壤中积累9,25,26。或者,土壤可生物降解的塑料覆盖物(BDM)被设计为在使用后耕种到土壤中,在那里它们会随着时间的推移而降解。然而,BDM暂时存在于土壤中,并逐渐降解并分裂成MP和NP9,27。
目前的许多环境生态毒理学和命运研究都采用了理想化和非代表性的MP和NP模型材料。最常用的替代MNP是单分散聚苯乙烯微球或纳米球,它们不反映实际驻留在环境中的MNP12,28。因此,选择不具代表性的国会议员和NP可能会导致不准确的测量和结果。由于缺乏用于陆地环境研究的适当模型ΜNPs,作者有动力用农用塑料制备此类模型。我们之前报道了通过塑料颗粒和薄膜材料的机械研磨和研磨从BDM和聚乙烯颗粒形成MNP,以及MNP29的尺寸和分子特性。目前的论文为制备MNP提供了更详细的方案,可以更广泛地应用于所有农用塑料,如地膜或其颗粒状原料(图1)。在这里,作为一个例子,我们选择了可生物降解聚合物聚对苯二甲酸丁二醇酯(PBAT)的地膜和球形颗粒来代表农用塑料。
该方法描述了最初在先前出版物29中描述的有效过程,以制备来自颗粒和覆盖膜的MNP用于环境研究。尺寸减小过程涉及低温冷却(仅适用于薄膜)、干磨和湿磨阶段,以制造模型MNP。我们已经应用这种方法从各种聚合物原料中制备MNP,包括低密度聚乙烯(LDPE),聚丁酸己二酸酯 – 共对苯二甲酸酯(PBAT)和聚乳酸(PLA)29 (Astner等人,手稿正在准备中)。然而,…
The authors have nothing to disclose.
这项研究由赫伯特农业学院,生物系统工程和土壤系以及田纳西大学诺克斯维尔分校的科学联盟资助。此外,作者非常感谢通过美国农业部拨款2020-67019-31167为这项研究提供的财务支持。用于制备基于PBAT的可生物降解地膜MNP的初始原料由BioBag美洲公司(美国佛罗里达州杜尼文)和莫比乌斯有限责任公司(田纳西州勒努瓦市)提供。
Aluminum dish, 150 mL | Fisher Scientific, Waltham, MA, USA | 08-732-103 | Drying of collected NPs |
Aluminum dish, 500 mL | VWR International, Radnor, PA, USA | 25433-018 | Collecting NPs after wet-grinding |
Centrifuge | Fisher Scientific, Waltham, MA, USA | Centrific 228 | Container for centrifugation |
Delivery tube, #20, 840 µm | Thomas Scientific, Swedesboro, NJ, USA | 3383M30 | Sieving of the first fraction during milling |
Delivery tube, #60, 250 µm | Thomas Scientific, Swedesboro, NJ, USA | 3383M45 | Sieving of the second fraction (3x) during milling |
Thermomixer, 5350 Mixer | Eppendorf North America, Enfield, CT, USA | 05-400-200 | Analysis of sieving experiments |
FT-IR Spectrum Two, spectrometer with attenuated total reflectance (ATR) | Perkin Elmer, Waltham, MA, USA | L1050228 | Measuring FTIR spectra |
Glass beaker, 1000 mL | DWK Life Sciences, Milville, NJ, USA | 02-555-113 | Stirring of MPs-water slurry before grinding |
Glass front plate | Thomas Scientific, Swedesboro, NJ, USA | 3383N55 | Front cover plaste for Wiley Mini Mill |
Glass jar, 50 mL | Uline, Pleasant Prairie, WI, USA | S-15846P | Collective MPs after milling |
Glove Box, neoprene | Bel-Art-SP Scienceware, Wayne, NJ, USA | BEL-H500290000 | 22-Inch, Size 10 |
Zetasizer Nano ZS 90 size analyzer | Malvern Panalytical, Worcestershire, UK | Zetasizer Nano ZS | Measuring nanoplastics dispersed in DI-water |
Microscope camera | Nikon, Tokyo, 108-6290, Japan | Nikon Digital Sight 10 | Combined with Olympus microscope to receive digital images |
Microscope | Olympus, Shinjuku, Tokyo, Japan | Model SZ 61 | Imaging of MPs |
Nitrogen jar, low form dewar flasks | Cole-Palmer, Vernon Hills, IL, USA | UX-03771-23 | Storage of liquid nitrogen during cryogenic cooling |
Accurate Blend 200, 12-speed blender | Oster, Boca Raton, FL, USA | 6684 | Initiating the size reduction of cryogenically treated plastic film |
PBAT film, – BioAgri™ (Mater-Bi®) | BioBag Americas, Inc, Dunedin, FL, USA | 0.7 mm thick | Feedstock to form MPs and NPs, agricultural mulch film |
PBAT pellets | Mobius, LLC, Lenoir City, TN, USA | Diameter 3 mm | Feedstock to form microplastics (MPs) and nanoplastics (NPs) trough milling and grinding |
Plastic centrifuge tubes, 50 mL | Fisher Scientific, Waltham, MA, USA | 06-443-18 | Centrifugation of slurry after wet-grinding |
Plastic jar, 1000 mL, pre-cleaned, straight sided | Fisher Scientific, Waltham, MA, USA | 05-719-733 | Collection of NPs during and after wet grinding |
Polygon stir bars, diameterø=8 mm, length=50.8 mm | Fisher Scientific, Waltham, MA, USA | 14-512-127 | Stirring of MPs slurry prior to wet-grinding |
Scissors, titanium bonded | Westcott, Shelton, CT, USA | 13901 | Cutting of initial PBAT film feedstocks |
Square glass cell with square aperture and cap, 12 mm O.D. | Malvern Panalytical, Worcestershire, UK | PCS1115 | Measuring of NPs particle size |
Stainless steel bottom, 3 inch, pan | Hogentogler & Co. Inc, Columbia, MD, USA | 8401 | For sieving after Wiley-milling |
Stainless steel sieve, 3 inch, No. 140 (106 µm) | Hogentogler & Co. Inc, Columbia, MD, USA | 1308 | For sieving after Wiley-milling |
Stainless steel sieve, 3 inch, No. 20 (850 µm) | Hogentogler & Co. Inc, Columbia, MD, USA | 1296 | Sieving of MPs after Wiley-milling |
Stainless steel sieve, 3 inch, No. 325 (45 µm) | Hogentogler & Co. Inc, Columbia, MD, USA | 1313 | Sieving of MPs after Wiley-milling |
Stainless steel sieve, 3 inch, No. 60 (250 µm) | Hogentogler & Co. Inc, Columbia, MD, USA | 1303 | Sieving of MPs after Wiley-milling |
Stainless steel top cover, 3 inch | Hogentogler & Co. Inc, Columbia, MD, USA | 8406 | Sieving of MPs after Wiley-milling |
Stainless steel tweezers | Global Industrial, Port Washington, NY, USA | T9FB2264892 | Transferring of frozen film particles from jar into blender |
Vacuum oven, model 281A | Fisher Scientific, Waltham, MA, USA | 13-262-50 | Vacuum oven to dry NPs after wet-grinding |
Friction grinding machine, Supermass Colloider | Masuko Sangyo, Tokyo, Japan | MKCA6-2J | Grinding machine to form NPs from MPs |
Wet-grinding stone, grit size: 297 μm -420 μm | Masuko Sangyo, Tokyo, Japan | MKE6-46DD | Grinding stone to form NPs from MPs |
Wiley Mini Mill, rotary cutting mill | Thomas Scientific, Swedesboro, NJ, USA | NC1346618 | Size reduction of pellets and film into MPs and NPs |
Software | |||
FTIR-Spectroscopy software | Perkin Elmer, Waltham, MA, USA | Spectrum 10 | Collection of spectra from the initial plastic, MPs and NPs |
Image J, image processing program | National Institutes of Health, Bethesda, MD, USA | Version 1.53n | Analysis of digital images received from microscopy |
Microscope software, ds-fi1 software | Malvern Panalytical , Malvern, UK | Firmware DS-U1 Ver3.10 | Recording of digital images |
Microsoft, Windows, Excel 365, spreadsheet software | Microsoft, Redmond, WA, USA | Office 365 | Calculating the average particle size and creating FTIR spectra images |
JMP software, statistical software | SAS Institute Inc., Cary, NC, 1989-2021 | Version 15 | Statistical analysis of particle size and perform best fit of data set |
Unscrambler software | Camo Analytics, Oslo, Norway | Version 9.2 | Normalizing and converting FTIR spectra into .csv fromat |