Department of Civil Engineering, The University of Memphis, Memphis, TN, USA.
108 Engineering Science Building, University of Memphis, Memphis, TN 38152, USA.
Sci Total Environ. 2022 Sep 15;839:156385. doi: 10.1016/j.scitotenv.2022.156385. Epub 2022 May 31.
The accelerated use of plastic products for agricultural practices has raised global concern regarding their negative impacts on soil health. This study aims to better understand the combined influence of polymer characteristics and environmental conditions on microplastic photodegradation within the agricultural soil system. For this purpose, the photodegradation behavior of low density polyethylene (LDPE) microplastics was studied through accelerated UVA radiation experiments under two different relative humidity (RH and RH) and soil deposition conditions. The variations of plastics' surface physiochemistry due to the accelerated photodegradation were studied using Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR), X-ray Photoelectron Spectroscopy (XPS), and Field Emission Scanning Electron Microscopy (FE-SEM). The carbonyl and vinyl indices were calculated using the ATR-FTIR information to compare the degree of microplastics' photodegradation. The plastics' bulk characteristics, including the percentage of crystallinity and molecular weight distributions, were examined using the Differential Scanning Calorimetry (DSC) and Gel Permeation Chromatography (GPC). Furthermore, the extent of UVA light interaction with the microplastics was studied by determining spectral quantum yield. The results demonstrated that new LDPE microplastics with a lower molecular weight (Mw = 233 kD) were subjected to a greater extent of photodegradation than those with greater molecular weight (Mw = 515 kD). Elevated relative humidity (RH) limited the photooxidation process of microplastics and consequently reduced the surface chemistry alterations. Deposition of soil particles with respect to the plastic particles impacted the photodegradation behavior. The microplastics covered by soil particles were not degraded, unlike those deposited next to the soil particles. The knowledge developed through this study could encourage the farmers and agricultural stakeholders to apply more efficient practices to remove plastic residuals after harvesting and conduct proper plastic disposal practices to protect soil health.
农用塑料制品的加速使用引起了全球对其对土壤健康负面影响的关注。本研究旨在更好地了解聚合物特性和环境条件对农用土壤系统中微塑料光降解的综合影响。为此，通过在两种不同相对湿度（RH 和 RH）和土壤沉积条件下进行加速 UVA 辐射实验，研究了低密度聚乙烯（LDPE）微塑料的光降解行为。使用衰减全反射傅里叶变换红外光谱（ATR-FTIR）、X 射线光电子能谱（XPS）和场发射扫描电子显微镜（FE-SEM）研究了由于加速光降解而导致的塑料表面物理化学性质的变化。使用 ATR-FTIR 信息计算了羰基和乙烯基指数，以比较微塑料光降解的程度。使用差示扫描量热法（DSC）和凝胶渗透色谱法（GPC）研究了塑料的体特性，包括结晶度百分比和分子量分布。此外，通过确定光谱量子产率研究了 UVA 光与微塑料的相互作用程度。结果表明，与具有较大分子量（Mw=515 kD）的微塑料相比，具有较低分子量（Mw=233 kD）的新 LDPE 微塑料受到更大程度的光降解。较高的相对湿度（RH）限制了微塑料的光氧化过程，从而减少了表面化学变化。相对于塑料颗粒沉积的土壤颗粒会影响光降解行为。被土壤颗粒覆盖的微塑料不会降解，而沉积在土壤颗粒旁边的微塑料则会降解。通过这项研究获得的知识可以鼓励农民和农业利益相关者在收获后应用更有效的实践来去除塑料残留物，并进行适当的塑料处理实践，以保护土壤健康。
