Plastic Bottles for Sorting Floating Microplastics in Sediment

Plastic waste's near-permanent pollution of the natural environment is becoming an increasing concern. It is necessary to determine the amount of microplastics (MPs) present in the natural environment and reduce the amount of plastic waste. In this study, the author developed a simple sorting method for MPs in sediment, which can eliminate sediment and does not require filtration, using an apparatus available to the public. This sorting method, called the "bottle method", can shut off floating matter from sediment and be used for sorting and washing at the same time. When the density of the solid sample is lower than the liquid density, the recovery rate is almost 100%, as theoretically predicted. The recovery rate of MPs by the bottle method is comparable to that by the other two methods, i.e., the spoon method and the overflow method, and the sorting time is reduced by approximately half. As for the dilution of the liquid by the bottle method, the ratio of actual concentration to theoretical concentration is in the range 0.86 to 1.36, and the dilution and washing of the liquid proceeds as theoretically predicted.