Microplastics and plastic-associated chemicals in the important green turtle nesting beaches in the Northwest Pacific

It is fundamental to understand the status of microplastic contamination in various sea turtle rookeries to assess the current and future effects of microplastics on sea turtles. The Ogasawara Islands, Tokyo, Japan, are the largest rookeries for green turtles (Chelonia mydas) in the Northwest Pacific and are remotely located 1,000 km from the Japanese mainland. To assess whether microplastic contamination occurred in the important nesting beaches of green turtles in the Northwest Pacific, we investigated the abundance and polymer types of microplastics collected at the surface and the nest depth (60 cm deep) in the sand of the 14 nesting beaches of the Ogasawara Islands. Results showed that microplastics were found at both the surface and the nest depth, and no significant difference in microplastic abundance was observed between them. The presence of microplastics at nest depth may be due to oceanographic and turtle nesting processes. Polystyrene, polypropylene, and polyethylene were identified, and expanded polystyrene was predominant. Furthermore, hexabromocyclododecanes, which are frequently compounded additives for expanded polystyrene, were semi-quantitatively analyzed using a pyrolizer coupled with a gas chromatograph-mass spectrometer in half of the expanded polystyrene microplastics collected in the present study. Result showed that hexabromocyclododecanes were detected in more than 30% of the analyzed microplastics, and the microplastics from both the surface and the nest depth contained hexabromocyclododecanes. The toxicological effect of such plastic-associated chemicals on turtles is a concern if they are transferable during egg incubation. Our data provide a baseline for assessing microplastic contamination in sea turtles on the Ogasawara Islands.