Fig. 3

Reference library spectra convey polymer relationships and patterns. (a) The wavenumber peaks for each polymer type are shown with color indicating relative intensity. Polymers are categorized by biological and anthropogenic sources and grouped by polymer type within those categories. (b) A cluster dendrogram showing similarities between specimen spectra. The hierarchical cluster analysis uses a Pearson’s distance matrix calculated between each pair of specimen spectra. Biological specimens are written in green and polypropylene specimens in blue. (c) Spectra for all polypropylene specimens within the library are visualized, demonstrating the effects of weathering, color, opacity, and individual sample on spectra variability. These spectra panels include three pristine and two weathered specimens, noted by (+) and (*), respectively. One weathered specimen (PLAS241) is unlabeled and sourced from a strawberry basket found in the Salinas River estuary, connecting to the Monterey Bay. Based on common industry manufacturing practices, this basket sample is likely polypropylene.