[M-IS17] Ocean Plastics, an earth science perspective

[MIS17-P06] Age estimate of polyethylene microplastics collected in oceans: an application to the western North Pacific

Rie Okubo¹, Aguru Yamamoto¹, Akihiro Kurima¹, Terumi Sakabe¹, Yoichiroh Ide¹, *Atsuhiko Isobe² (1.Asahi Kasei, 2.Kyushu University)

Keywords:microplastics, carbonyl index

Microplastic ages defined as the exposure time to ultraviolet (UV) radiation were estimated using the carbonyl index computed by infrared spectrometry, UV erythemal radiation (UVER or UV index) in meteorological records, and ambient seawater temperature in oceanographic records. A set of accelerated and outdoor exposure experiments were conducted to find a relationship among temporally integrated UVER, ambient temperature, and carbonyl index. Thereafter, ages (exposure time to UV radiation) of microplastics with Miyakojima Island as the reference point were computed. The microplastics collected in the western North Pacific demonstrated that their ages in the open ocean were concentrated within a range between 1 and 3 years, while the ages estimated in the nearshore waters were ranged between 0 and 5 years. The spatial distribution of ages suggested that microplastics generated mostly on land degrade continuously even in the ocean, and that microplastics in the offshore waters were removed from the upper ocean to subsurface layers via biological processes within a timescale of a few years.