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，食品包装与加工过程可能是微塑料（microplastics）的污染来源之一。本研究采用显微拉曼（micro-Raman, µ-Raman）光谱技术，对5台分别配备塑料与陶瓷材质研磨磨刃的盐磨设备在研磨过程中产生的颗粒磨损产物开展分析。实验中将参比盐装入盐磨，取0.1g经研磨后的样品转移至烧杯中，经溶解、过滤后，对起始粒径≥1μm的不同粒径分级残留物采用µ-Raman光谱进行分析。未研磨的参比盐本身中，每0.1g可检出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），且该本底含量未从后续样品的检测结果中予以扣除。其中1台采用陶瓷磨刃的盐磨仅释放出PET颗粒（每0.1g含527±265个）；另一台陶瓷磨刃盐磨的研磨系统内含有聚苯乙烯（polystyrene, PS）组件，研磨后的盐样中检出两类颗粒：201±37个PET颗粒与727±226个PS颗粒。2台塑料材质盐磨的磨刃采用聚甲醛（polyoxymethylene, POM）制作，剩余1台的磨刃为聚甲基丙烯酸甲酯（poly(methyl methacrylate), PMMA）材质。两台POM磨刃盐磨的0.1g盐样中，分别检出7628±2655个与5048±594个POM颗粒，同时还分别检出265±182个与1546±884个PET颗粒；PMMA磨刃盐磨对应的盐样中，则检出240±41个PMMA颗粒/0.1g，以及1643±1174个PET颗粒。绝大多数PET颗粒粒径小于5μm，而POM、PS与PMMA颗粒的平均粒径均大于10μm。除盐本身可能携带微塑料污染外，配备塑料磨刃的盐磨设备可大量释放微塑料颗粒，尤其当磨刃采用POM材质时。但研磨设备同时也可能释放其他类型的颗粒，例如同粒径范围的陶瓷颗粒，这引发了一个问题：究竟哪些颗粒、以及何种类型的颗粒会对人体产生毒理学层面的健康风险。