The combination of spectroscopy, microscopy, and profilometry methods for the physical and chemical characterization of environmentally relevant microplastics

Environmental pollution related to microplastics (MPs) is a growing concern across the globe. In addition to the primary concern of MP levels in the environment, they have also been known to sorb a variety of organic materials, concentrating and transporting them into the environment and aquatic life. The focus of this study was to evaluate differences in surface characteristics and chemical composition of neat MP standards relative to MP samples extracted from personal care products and wastewater effluent. MPs were first chemically characterized using Attenuated Total Reflectance (ATR) Fourier Transform Infrared Spectroscopy (FT-IR) to determine their composition, then physically characterized using Scanning Electron Microscopy (SEM) and Optical Profilometry (OP). Under SEM and OP imaging, neat polyethylene MP standards appeared uniform in spherical shape with a smooth surface displaying shallow pitting. MPs extracted from personal care products were characterized as polyethylene and many of these samples displayed a significant distortion from the spherical shape of the neat standards with crevices ranging at various depths. MPs extracted from a Waste Water Treatment Plant (WWTP) effluent tank were characterized as polyethylene and other unidentified plastic polymers. Through SEM and OP, the WWTP effluent extracted MPs were seen to have similar surface characteristics to the personal care product extracted spherical MPs, demonstrating deep pits and large flat top peaks. OP was used to quantitatively compare the MPs by three surface roughness parameters. This proof-of-concept study is the first to utilize FT-IR, SEM and OP for the surface characterization of MP samples. Combining these three methods allows for the chemical identification of MPs along with the qualitative and quantitative comparison of their surface characteristics, demonstrating that MPs extracted from personal care products and WWTP effluent differ greatly from neat microsphere standards of similar sizes.