Determination of particle abrasion through milling with five different salt grinders – a preliminary study by micro-Raman spectroscopy with efforts towards improved quality control of the analytical methods

Latest findings suggest that packaging and processing of food may be a contamination source of microplastics. In this study particle abrasion from five different salt mills with grinding burrs made of plastic and ceramic were investigated using micro-Raman (µ-Raman) spectroscopy. The mills were filled with a reference salt and an amount of 0.1 g was milled into a beaker, dissolved, filtered and the residues analysed via µ-Raman spectroscopy in different size classes, beginning with ≥ 1 µm. In the unground reference salt itself 423 ± 161 microplastic particles per 0.1 g were found, mainly consisting of polyethylene terephthalate (PET). These contents were not subtracted from the samples. One of the ceramic grinders also exclusively released PET-particles (527 ± 265 per 0.1 g).The other had compartments of polystyrene (PS) in the milling system and PS particles were found in the ground salt (201 ± 37 PET; 727 ± 226 PS/). Two of the plastic grinders had burrs made of polyoxymethylene (POM) and one with burrs of poly(methyl methacrylate) (PMMA). There were large amounts of 7628 ± 2655 and 5048 + 594 POM particles in 0.1 g salt in the two POM grinders as well as 265 ± 182 and 1546 ± 884 PET particles, respectively; salt from the PMMA grinder had 240 ± 41 PMMA particles/0.1 g and 1643 ± 1174 PET particles. The majority of the PET particles were smaller than 5 µm, whereas the POM, PS and PMMA particles had average sizes greater than 10 µm. In addition to possible microplastic contamination from salt itself, salt mills with grinding burrs made of plastic can emit microplastic particles in large amounts, especially if the burrs are made of POM. Other particles may, however, also be emitted from the grinders, e.g. ceramic particles in a similar size class, leading to the question whether and which kind of particles may be of toxicological concern for humans.

最新研究表明，食品的包装与加工过程可能是微塑料的污染源之一。本研究采用显微拉曼（micro-Raman, µ-Raman）光谱技术，对5台分别采用塑料和陶瓷磨齿的盐磨设备产生的颗粒磨损情况展开了系统探究。实验中，将基准食盐装入磨盐机，每次取0.1 g经研磨后转移至烧杯，经溶解、过滤后，针对起始粒径≥1 μm的不同粒径等级的残留颗粒，采用显微拉曼光谱进行分析。在未经研磨的基准食盐样品中，每0.1 g样品检出423 ± 161个微塑料颗粒，其主要成分为聚对苯二甲酸乙二酯（polyethylene terephthalate, PET），该本底含量未从后续样品的检测结果中扣除。其中一台陶瓷磨齿机仅释放聚对苯二甲酸乙二酯颗粒，每0.1 g样品检出量为527 ± 265个。另一台陶瓷磨齿机的研磨系统中含有聚苯乙烯（polystyrene, PS）组件，经研磨的食盐中检出了PS颗粒（201 ± 37个PET颗粒，727 ± 226个PS颗粒）。两台塑料磨齿机的磨齿材质为聚甲醛（polyoxymethylene, POM），另有一台的磨齿材质为聚甲基丙烯酸甲酯（poly(methyl methacrylate), PMMA）。两台POM磨齿机研磨得到的食盐中，分别检出7628 ± 2655和5048 ± 594个POM颗粒，同时分别检出265 ± 182和1546 ± 884个PET颗粒；PMMA磨齿机研磨得到的食盐中，每0.1 g样品检出240 ± 41个PMMA颗粒以及1643 ± 1174个PET颗粒。绝大多数PET颗粒的粒径小于5 μm，而POM、PS及PMMA颗粒的平均粒径均大于10 μm。除食盐本身可能带来的微塑料污染外，使用塑料磨齿的盐磨设备可大量释放微塑料颗粒，尤其当磨齿材质为聚甲醛时。不过，磨齿设备也可能释放其他类型的颗粒，例如同粒径范围的陶瓷颗粒，这引发了一个值得探讨的问题：究竟哪些类型的颗粒会对人体产生毒理学层面的健康风险。