Investigating microplastics at two drinking water treatment plants within a river catchment

Microplastics (MPs) are emerging globally distributed pollutants of aquatic environments. Nowadays, MPs are being detected in seas, oceans and freshwater bodies worldwide, even in very remote areas. Studies have reported also the occurrence of MPs in potable water. Despite the potential adverse effects on human health are still largely unknown, the presence of MPs in drinking water deserves more attention. Besides the need for elimination of MPs in natural environments, it is necessary to focus also on their fate and removability at drinking water treatment plants (DWTPs) that pose a barrier for MPs to enter water for human consumption. In our study, we decided to provide unique insight into the occurrence of MPs at two different DWTPs situated on the same river but differing in treatment technology. Quantification and characterization of MPs ≥ 1 μm was conducted not only in raw and treated water but also after each technological treatment step. The results showed that the content of MPs varied greatly between the DWTPs. There were 23 ± 2 and 14 ± 1 MPs L⁻¹ in raw and treated water, respectively, at the upstream DWTP. By contrast, 1296 ± 35 and 151 ± 4 MPs L⁻¹ were found in raw and treated water, respectively, at the downstream DWTP. The majority (>70%) of MPs were smaller than 10 μm, and irregular fragment shape prevailed over fibres. Cellulose acetate, polyethylene terephthalate, polyvinyl chloride, polyethylene, and polypropylene were the most frequently occurring materials. Total removal of MPs of 88% was achieved at the DWTP with a higher initial MP number and more complicated treatment technology consisting of coagulation-flocculation-sedimentation, deep-bed filtration through clay-based material, and granular activated carbon adsorption. These steps contributed to MP elimination by 62%, 20%, and 6%, respectively. These results contribute to filling the knowledge gap regarding the removability of different types of MPs by distinct drinking water treatment technologies operating under ordinary conditions.