A year-long field study of buried plastics reveals underestimation of plastic pollution on Hawaiian beaches

Abstract

Global models estimate that two-thirds of floating ocean plastic has accumulated in coastal areas since the 1950s, with Hawaiʻi’s windward shores particularly vulnerable due to their proximity to the North Pacific Garbage Patch. Our quarterly surveys revealed that 91 % of recovered plastic particles were buried below the surface (deeper than 2 cm), with most particles being small fragments (93 %) with an average mean max length of 6.7 ± 4.4 mm. This study offers new insights into subsurface plastic, exposing a previously hidden vertical distribution of plastic pollution. We observed significant variations in plastic abundance across depths, beaches, and sampling periods, along with a positive correlation between particle size and sand grain size. Additionally, through reconciliation science, we critically reflect on the cultural impacts of our research, emphasizing the importance of aligning plastic pollution studies with local community values and environmental stewardship.