# Notes on Common Misconceptions in Microplastics Removal from Water
It has been pointed out that 95% of all microplastics in water are smaller than 10 \(\upmu\)m (the particles were divided into six fractions by total count: 0.2-1 \(\upmu\)m; 1-5 \(\upmu\)m; 5-10 \(\upmu\)m; 10-50 \(\upmu\)m; 50-100 \(\upmu\)m; >100 \(\upmu\)m). The most dominating representatives were PET, PP and PE and the dominating forms were fragments of undefined shapes and fibres. The removal efficiency of treatment processes in monitored drinking water treatment plants was 83% on average. According to absolute concentrations of microplastics before and after treatment (3605 \(\pm\) 497 particles L\({}^{-1}\); 628 \(\pm\) 28 particles L\({}^{-1}\)) and considering no specialised method for their removal, a significant decrease was observed. However, space for improvement still exists. Another study of the same research group investigated the influence of the size and shape of microplastics on their removal efficacy at various stages of water treatment in two drinking water treatment plants [28]. It was determined that coagulation/flocculation was not influenced by the size and shape of particles, while consecutive filtration through clay material improved removal of particles larger than 50 \(\upmu\)m and granular activated carbon improved removal of particles larger than 10 \(\upmu\)m. The influence of their shape is yet to be determined. It was also shown that the most prevailing shape of microplastics was undefined fragment. One of the important sources of microplastic particles in water is the washing of synthetic materials in households. This wastewater is further treated in wastewater treatment plants from where they can enter watercourses in nature [29; 30; 31]. All possible sources of microplastics in the environment are presented by [PERSON] et al. in a well arranged way. The authors compare distribution of microplastics in different urban environments around the world and they conclude that microplastic may form an internal circulation, where human beings and aquatic organisms are continuously exposed to them [32]. [PERSON] et al. (2017) have investigated how many microplastics can be captured by different wastewater treatment plant processes (membrane bioreactor as representative of primary stage treatment; filtrations and flotation as representatives of tertiary treatments). The device containing the membrane bioreactor was able to remove up to 99% of microplastics, the rapid sand filter 97%, flotation removed 95% of particles and the disc filter 40-98% of contained microplastics [29]. This is seemingly a very nice result; however, the major drawback of this study was the range of detected microparticles--particles smaller than 20 \(\upmu\)m were not detected. [PERSON] et al. [33] studied the presence of microplastics in drinking water originating from groundwater and determined the content of microplastics was only 0.7 particles per m\({}^{3}\). However, this may be due to the fact that, again, the lower limit of the measurements was 20 \(\upmu\)m. [PERSON] et al. [34] determined microplastic particles in more than 30 samples of bottled water. Samples in glass bottles contained 2649-2857 particles L\({}^{-1}\) and samples in PET bottles 6292-10,521 particles L\({}^{-1}\). The authors also identified additives, such as pigment (from bottle labelling) or tris(2,4-di-tertbutylphenyl)phosphine (from the bottle material itself). Both in PET and glass bottles they found out that 90% of microplastic particles were smaller than 5 \(\upmu\)m and 40% were smaller than 1.5 \(\upmu\)m [34]. The authors correctly pointed out that a thoroughgoing analysis of particles smaller than 1 \(\upmu\)m is crucial in order to evaluate the number of particles that can be ingested and to determine their possible toxicological effect. One can expect that what is suitable for microparticles with mm dimensions is not applicable for particles with nm dimensions. A simple comparison between published studies is therefore hardly feasible and a more complex approach is needed.