Fig. 4

Spectra of unknown plastics found in the environment can be matched to known spectra in the reference library. The spectrum from a weathered strawberry basket (red, bottom) collected from an agricultural region of the Salinas River watershed matched with spectrum of a pristine polypropylene specimen (red, second to bottom), and was confirmed using S&N’s plastics library. In contrast, the strawberry basket spectrum did not covary with other spectra in the library. Example spectra from pristine and weathered anthropogenic polymers and a biological polymer are displayed in top panels for comparison. Gray dashed lines denote matched spectral peaks for illustrative purposes - matching was done quantitatively using the Pearson distance matching protocol (see Methods).