Estimation of the age of polyethylene microplastics collected from oceans: Application to the western North Pacific Ocean.

The knowledge of microplastic (MP) age could aid the deduction of the origin and fate of a fragment carried by ocean currents over long time periods and distances. The present study developed a novel method to estimate the age of MPs (i.e., UV radiation exposure time) using the oxidation level of polyethylene (i.e., carbonyl index) from infrared spectrometry, ultraviolet erythemal radiation (UVER) data, and ambient seawater temperatures. Accelerated and outdoor exposure experiments were conducted to establish relationships among the temporally integrated UVER, ambient temperature, and carbonyl index. Thereafter, the age of MPs was computed, with Miyakojima Island serving as the reference location. The estimated ages of MPs collected from the western North Pacific Ocean ranged from 1 to 3 years, and those MPs from nearshore waters ranged from 0 to 5 years.

Analysis of cross-section structure of a polymer wrapping film using infrared attenuated total reflection imaging technique with an aid of chemometrics.

Infrared microscopic imaging techniques with an aid of augmented alternative least-squares (ALS) regression analysis have been employed for analyzing the interface structure involved in two wrapping films that have a common layered structure with different adhesive intermixing between the adjacent layers. A conventional single-band mapping technique exhibited a problem that the imaging results responded to the selection of an analytical band. On the other hand, the augmented ALS technique has proved to powerfully decompose the collection of spectra into spectroscopically independent spectra and quantity variations in the mapping area. Regardless, the chemometric analysis could not commonly be applied to the two films, and different pretreatments were necessary for analysis of the two films. As a result, the concentration profiles across the boundaries have readily revealed that the two films have largely different adhesive structures. In addition, the structural difference was found to be a reason an identical analytical technique cannot be employed for analysis of the two films. This study shows an appropriate pretreatment and selection of a chemometric technique considering the samples that have different spectroscopic characters are of great importance for effectively draw map images and pure-component spectra of the constituents.