a. MORPHOLOGY - according to the observable structure of microplastics under the microscope, similar to shape but has a more definitive characterization (e.g. filament, fragment, film, pellet, foam)

b. SHAPE - according to observable physical characteristics of microplastics under the microscope that resemble common shapes. Some are in their common observable or natural shape (e.g. ovoid, rounded) or in their decomposed or fractured or unnatural shape (e.g. degraded, irregular)

c. POLYMER TYPE - according to the chemical composition of the plastic (e.g. PP, PE, PET)

d. COLOR - classifications are according to the observable color of the microplastics with or without the use of a microscope (e.g. blue, green, white)

e. PRODUCT - classifications according to the intended uses or general function of the plastics as industrial or commercial products (e.g. bottles, utensils, rope)

**Counts for category classes that are not reported in the source literature are encoded as zero