The determination of microplastic contamination in freshwater environments using sampling methods – A case study

We compared different net sampling methods for microplastic quantitative collection by sampling different water volumes with nets of different mesh sizes. Sampling covered freshwater lake and reservoir with a significant degree of eutrophication located in Central Poland. The fibres were the main type of plastic collected from sampling sites and constituted 83% of all microplastic particles. Fibres of 700–1900 μm dominated in the samples. The size of mesh affected the amount of fibres collected. Small fibres of 10–200 μm in length were collected using only a fine net of 20 μm mesh size. The total amount of fibres depended on sample volumes; concentrations of microplastics were higher for smaller water volumes. It is likely that clogging with phytoplankton and suspended particles reduced the filtration capacity of the finest nets when large volumes were sampled, which led to an underestimation of microplastic. To our knowledge, this is the first study to provide evidence that the amount of small microfibres depends on mesh size and that the total microplastic abundance in freshwaters in Poland depends on the sample volume. We suggest sampling rather larger than smaller water volumes to assess the level of microplastic contamination more accurately, but clogging, which reduces the filtration capacity of finest nets, should be taken into account when eutrophic freshwater environments are studied.