Organo-mineral interaction is an important mechanism affecting the fate of natural organic matter in the environment. Field discoveries since 2014 report a novel type of organo-mineral interaction, where “recalcitrant” plastic polymers either physically or chemically attach onto or fuse into host rocks or sediments. During our previous field observation in 2022, it was reported that weathered low-density polyethylene (LDPE) plastic films were chemically attached onto sedimentary rocks. It was hypothesized that sunlight irradiation may have triggered chemical interactions following physical attachment of plastic film onto rock surfaces. In this study, we tested this hypothesis through accelerated aging experiments. Specifically, we first explored the interaction mechanisms between low-density polyethylene film and crushed sedimentary rock powders, including sandstone, shale, limestone, and ironstone, through accelerated UV irradiation ranging from 0 to 168 h. Subsequently, we conducted experiments using the plastic film and consolidated shale rocks. We found that chemical binding took place after 48 h of UV irradiation equivalent to 35 days of exposure of plastic film to sunlight on the land surface. The organo-mineral interaction process started with the surface oxidation of plastic film leading to the generation of carbonyl and ether groups. After that, irreversible mineral binding occurred. Visualization of the plastic films following the aging experiments showed that mineral particles were incorporated within the polymer instead of surface attachment. Organo-mineral interaction mechanisms between LDPE film and sedimentary rocks were further explored via multiple approaches including XPS, STEM-EELS, TOF-SIMS, and theoretical calculations. Multiple lines of evidence suggested binding mechanisms for this process, including the formation of chemical bonds such as Si-O-C, corroborating well with our previously reported field findings. The findings of this study offer robust evidence that natural weathering processes, such as sunlight irradiation, can initiate chemical reactions between plastic and rock materials, deepening our understanding of plastic pollution dynamics within the geological context.

中文翻译：

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紫外线照射引起的塑料薄膜与沉积岩之间的有机矿物相互作用


有机-矿物相互作用是影响环境中天然有机物命运的重要机制。自 2014 年以来的现场发现报告了一种新型的有机矿物相互作用，其中“顽固的”塑料聚合物以物理或化学方式附着或融合到主岩或沉积物中。在我们之前 2022 年的实地观察中，据报道，风化的低密度聚乙烯 (LDPE) 塑料薄膜通过化学方式附着在沉积岩上。据推测，塑料薄膜物理附着在岩石表面后，阳光照射可能引发化学相互作用。在这项研究中，我们通过加速老化实验检验了这一假设。具体来说，我们首先通过0至168小时的加速紫外线照射，探索了低密度聚乙烯薄膜与碎沉积岩粉末（包括砂岩、页岩、石灰岩和铁矿石）之间的相互作用机制。随后，我们使用塑料薄膜和固结页岩进行了实验。我们发现，在紫外线照射 48 小时后，相当于塑料薄膜在陆地表面暴露在阳光下 35 天，就会发生化学结合。有机矿物相互作用过程始于塑料薄膜的表面氧化，导致羰基和醚基团的生成。此后，发生不可逆的矿物结合。老化实验后塑料薄膜的可视化表明，矿物颗粒被纳入聚合物内，而不是表面附着。通过XPS、STEM-EELS、TOF-SIMS和理论计算等多种方法进一步探讨了LDPE薄膜与沉积岩之间的有机矿物相互作用机制。 多种证据表明该过程的结合机制，包括形成 Si-OC 等化学键，这与我们之前报道的现场发现得到了很好的证实。这项研究的结果提供了强有力的证据，证明自然风化过程（例如阳光照射）可以引发塑料和岩石材料之间的化学反应，加深我们对地质背景下塑料污染动态的理解。