Temporal Variability of Microplastic Concentrations in Inland Waters: An Automated, Semicontinuous Sampling of Microplastics ≥11 μm in a Stream in Southern Germany

To advance understanding about the temporal variability of microplastic concentrations in inland waters, this study presents a fully automatic sampling unit for microplastics (SAM), which collects daily mixed samples using fractionated filtration. Method validation with five different polymer types revealed an overall recovery of 77 ± 29% for sampling, sample preparation, and analysis of particles ≥11 μm using Fourier transform infrared micro spectroscopy. During an 8 day field test, SAM was applied in a stream in Southern Germany. Microplastic concentrations in the daily mixed samples differed by a factor of 10.8 within the study period, ranging from 1210 to 13 052 particles and fibers per m3. Polypropylene and polymer cluster acrylates/polyurethanes/varnish were the most abundant polymer types observed. The comparison of day-to-day variability of microplastic concentrations with the total particle count, turbidity, precipitation, as well as discharge in the stream did not reveal distinct interrelations. The field application, as well as the good recovery rates of SAM, demonstrate its suitability for future long-term studies focusing on the temporal variability of microplastic concentrations.