Quantitative Identification of Microplastics in Water Using Nile Red Staining

The development of methods used for evaluating the presence of microplastics (MPs) in water is now an interesting issue since there were many studies, reporting negative impacts of MPs in water on living organisms and the environment. At present, fluorescent dye staining is an extensively used technique for the quantitative and particle size determinations of MPs in water, because this technique is simple and fast.
In this study, this technique together with the use of Nile Red dye (NR), microscope, and ImageJ software was employed to identify the number and particle size of polyethylene MPs (PE-MPs) in water. Two major factors considered in this present work were the effects of NR concentrations ([NR]) in water sample and NR incubation times on quantitative and particle size identifications of PE-MPs in water. Considering these factors and the study results, it was found that [NR] = 1 and 2 µg/mL and NR incubation time of 30 min were the appropriate condition for quantitative identification of PE-MPs in water, and the smallest and largest particle sizes of PE-MPs detected were 5.38 and 98.2 µm. It is, therefore, obvious that NR staining technique is a suitable method for assessment of the existence of PE-MPs, with size in the range of 5 to 100 µm, in water.