In a study published recently [87], the occurrence and distribution of microplastics in samples from municipal, industrial, and agricultural wastewater sources (9 domestic, 5 industrial plants, 10 industrial, 4 livestock holdings, and 4 fishponds) from a specific area in China were investigated. The water samples were enzymatically treated, then oxidized with hydrogen peroxide. The MPs were separated based on their density, characterized by micro-Raman spectroscopy, and classified by shape, size, and color. According to their results, the water from domestic wastewater treatment plants contained 18–890 pcs/L MP pollutants in the influent and 6–26 pcs/L in the effluent, the removal efficiency was between 35–98%. The effluents from industrial wastewater treatment plants contained 6-12 pcs/L, the level of MPs in the effluents from industrial plants, livestock holdings and fishponds was in the range of 8–23, 8-40 and 13–27 pcs/L. It was found that the amount of MPs in wastewaters from different sources did not show any significant difference. In terms of material quality, PE, PP, and PS accounted for nearly 83% of the total content of MP. Most of the MP particles were smaller than 500 μm, and as regards shape, fragment and film were the most common. The type of polymer (PE, PP, PS, PVC, PET, PA) and shape did not change statistically significantly in the different sources, but there were slight differences in the size and color of the MPs from the different sources.

The distribution of microplastic particles was investigated in surface water and sediment samples collected from ten sites along a river flowing through a slum and industrial area in Indonesia [88]. The microplastic particles were identified with a binocular microscope and categorized according to their shape and size. The mean concentration was 5.85 ± 3.28 particles/L surface water and 3.03 ± 1.59 particles/100 g dry sediment. In the sediment samples, the concentration of microplastic changed significantly with land use, while no significant differences were found in the water samples. The microplastic particles were predominantly composed of fiber particles. Various fiber forms can be formed from the direct clothing of river residents and from the fabric washing process of the textile industry. According to Raman spectroscopy tests, the material type of the particles is polyester and nylon.

Several articles address the release of microplastic fibers from synthetic (e.g. polyester) textiles into surface water and air during washing. It was found that most MP fibers are released during delicate washes with a larger volume of water [89]. Microfibers have been identified as the main form of microplastics in fresh waters, and the washing of synthetic textiles as one of their main sources [90]. Standardized washing tests were performed on 12 different samples consisting of representative fibers and textile types and highly variable results were obtained, the amount of released fibers with an average length of 165–841 μm varied between 210–72000 pcs/g textile/wash.

In Germany, bank sediments from the Rhine and Main rivers were analyzed. Samples were collected from the bank sediments of a large European river (Rhine) and an industrially influenced river (Main) in areas of variable population size and in areas close to nature reserves [91]. All investigated sediments contained microplastic particles (< 5 mm) in the amount of up to 1 g/kg or 4000 particles/kg. Analysis of the plastics by infrared spectroscopy explored high amounts of polyethylene, polypropylene, and polystyrene, covering more than 75% of all polymer types identified in the sediments. Their results showed high concentrations of microplastics, similar to those found in polluted marine sediments. The spatial variation in the concentration of microplastics and polymer preparations at all sampling sites showed no correlation with the population density or the proximity of the industrial area to the wastewater treatment plants. The authors emphasized the transport of plastic particles from river to river and found that as a result rivers transport microplastic particles to the ocean.