EFFECTIVENESS OF ATR-FTIR FOR ANALYSIS OF MICROPLASTICS FROM MARINE AND FRESHWATER SEDIMENTS

Nurdles, i.e., preproduction microplastics (< 5 mm), are an emerging contaminant in marine and freshwater environments. An estimated 230,000 MT of nurdles are released annually into the world’s oceans from offshore spills and improper management by manufacturers and users. FTIR is one of the most common techniques for characterizing microplastics; unfortunately, however, the interpretation of FTIR analysis varies in the published literature. ATR-FTIR techniques used in this analysis allowed for rapid identification of field specimens. In addition, proper sample preparation allowed for removal of more loosely adhered sediments and affords clarity to the IR spectra of the nurdle. Four hundred sixteen nurdles were collected from marine and freshwater sites and were visually separated based on color and shape. Infrared spectra were obtained of unrinsed, rinsed, and sonicated nurdles. ATR spectra of the unrinsed polymers revealed that the composition of those samples was 96.5% polyethylene (PE) and 3.5% polypropylene (PP). Key bands in the spectra of unrinsed PE and PP were visible even among samples where sediment was visually present. Identification of components was made by comparison with reference spectra. A total of 90 marine and 82 freshwater samples were randomly selected for the rinse and sonicate treatments. Kaolin, calcium carbonate, and quartz bands were common across all samples. Sometimes IR bands appeared in regions that are consistent with thermo- and photooxidation of PE. The presence of IR bands from sorbed components on nurdles makes accurate analysis problematic. With each subsequent stage of rinsing, the silicate bands of kaolin decreased relative to methylene bands of the polymer. The only exception to these findings was the relatively minor change in the silicate bands of yellowed polymers. Based on preliminary data, a significant portion of the silicates remain sorbed to particles. The literature indicates that the presence of clays will likely increase the ability of particles to sorb contaminants such as hydrocarbons and heavy metals. ATR-FTIR analysis is an ideal instrument for analysis of polymers going from field to laboratory with little or no sample preparation. Studies examining the distribution of microplastics would be well served to use ATR to reduce analysis time significantly.