COMPARATIVE ANALYSIS OF PHYSICAL AND CHEMICAL WEATHERING OF NURDLES IN MARINE AND FRESHWATER ENVIRONMENTS

Nurdles, i.e., pre-production microplastics (< 5 mm), are the raw material used to produce countless plastic products. It is currently estimated that over 2 trillion nurdles enter the environment annually due to improper management by manufacturers, offshore spills, and other aspects of transport. Fish and other aquatic organisms have been documented to actively and passively ingest microplastics. Investigating the physical and chemical degradation of nurdles can be used to estimate how long they have been in the environment and offer insights into nurdle weathering, i.e., how they interact with the environment. Approximately 500 nurdles were collected from marine (Oregon coast) and freshwater sites (Lake Michigan coast). Visual determination of physical weathering was completed using a stereomicroscope, and ATR-FTIR was used to determine nurdle chemical composition. Nurdles were separated in the laboratory based on shape, degree of yellowing, and physical weathering. Yellowing of plastic, an indicator of chemical degradation, was categorized from 0 (none) to 3 (significant). Chi-square tests indicated a relationship between yellowing and abrasions (p < 0.001) and cracks (p < 0.001) but not between yellowing and presence of etching (p = 0.15). Total coverage of etching, cracks, and abrasions tended to increase with yellowing. A combination of these factors might be utilized to estimate the relative length of time a nurdle has been present in the environment. Physical differences in particles between marine and freshwater environments were noted. Freshwater samples exhibited a higher prevalence of etching; in contrast, nurdles in the marine environment displayed slightly higher yellowing and total physical weathering. This study will be expanded to include data from samples collected in the Gulf of Mexico and investigate the presence of new functional groups in ATR spectra, indicative of oxidation of polymers. The additional data will provide an opportunity to compare the properties of nurdles in different marine environments and advance our understanding of the physical and chemical changes that occur after nurdles are introduced to the environment.