Facile, inexpensive, and reliable morphological characterization of microplastics using Optical Microscopy images

Abstract

A morphological classification method was developed and applied to model contaminants of polyethylene microplastics (MPs) obtained in the laboratory by simple procedures. Primary MPs were produced by pump-assisted aqueous isolation from a commercial cosmetic cream, and secondary MPs were obtained by mechanical abrasion from a domestic plastic can. The MPs were investigated by optical microscopy and their images were analyzed according to forms and types of edge by means of a self-written Python-based script. Four simple geometrical forms were employed to classify the MPs, i.e., fiber, ellipse, triangle, and quadrilateral shapes, while their edges were defined as plain, wavy, lobed, and filiform, quantifying each type of edge on every MP. In addition, the numerical results provided by the computational analysis were employed to develop two complimentary indexes, R and I, associated to the degree of surface roughness and smoothness, ranging from 0 to 1 for the quantitative morphological characterization of the regularity and irregularity, respectively, of the particles. Thus, an inexpensive and simple but rigorous detailed physical characterization for MPs is provided, which can be particularly helpful for monitoring the changes that these particles may undergo in the environment.