Microplastic analysis in drinking water based on fractionated filtration sampling and Raman microspectroscopy

Microplastics (MP) as emerging persistent pollutants were found in raw and drinking water worldwide. Since different methods were used, there is an urgent need for harmonized protocols for sampling, sample preparation, and analysis. In this study, a holistic and validated analytical workflow for MP analysis in aqueous matrices down to 5 μm is presented. For sampling of several cubic meters of water, an easily portable filter cascade unit with different pore sizes (100-20-5 μm) was developed and successfully applied for the sampling of three processed drinking waters, two tap waters and one groundwater. The size distribution and polymer types of MP were determined using a two-step semi-automated Raman microspectroscopy analysis. For quality control, comprehensive process blanks were considered at all times and a recovery test yielded an overall recovery of 81%. The average concentration of identified MP was 66 ± 76 MP/m³ ranging from 1 MP/m³ to 197 MP/m³. All found concentrations were below the limit of quantitation (LOQ) of 1880 MP/m³. The majority consisted of PE (86% ± 111%) while comparatively low numbers of PET (10% ± 25%), PP (3% ± 6%), and PA (1% ± 4%) were found. 79% of all particles were smaller than 20 μm. In summary, this study presents the application of a workflow for sampling and analysis of MP down to 5 μm with first results of no significant contamination in drinking water and groundwater.