Plastic Particles and Grain Analyses in the Sand of Tetiaroa Atoll

Katherine Lasdin^1*Katherine Shaw^2,3Romina Centurion¹Marjorie Cantine⁴Núria Viladrich^5,6Jacqueline L Padilla-Gamino¹

• ¹University of Washington, School of Aquatic and Fishery Sciences, Seattle, United States
• ²National Institute of Standards and Technology, Waimanalo, United States
• ³Hawai'i Pacific University Center for Marine Debris Reserach, Waimanalo, United States
• ⁴Department of Earth and Space Sciences, University of Washington, Seattle, United States
• ⁵Depertament de Biologia Evolutiva, Ecologia i Ciències Ambientals, Universitat de Barcelona, Barcelona, Spain
• ⁶Institut de Recerca de la Biodiversitat (IRBio), Universitat de Barcelona, Barcelona, Spain

Abstract (300 words): Quantifying plastic debris in remote and pristine natural environments is critical for assessing the extent of global pollution and its potential effects on biodiversity. This study assessed the abundance and composition of plastic particles in the sand of Tetiaroa Atoll (French Polynesia), a sanctuary for diverse marine and terrestrial organisms. Sand samples were collected from ocean-facing and lagoon-facing beaches across 12 motus (islets) of Tetiaroa Atoll. Particles larger than 1 mm were extracted via two density separations and vacuum filtration, followed by polymer identification via Attenuated Total Reflection - Fourier Transform Infrared Spectroscopy (ATR-FTIR), and a total of 275 plastic particles were verified. These plastic particles were sorted into seven morphological types and ranged in length from 1 to 36 mm. Nine polymers were found; polyethylene (PE) was the most common polymer (35.5%), followed by polypropylene (PP) (23%) and PE-PP blends (11.9%). Plastic abundance varied, ranging from 0 to 25.09 pieces/kg of sand, with differences observed between lagoon-facing and ocean-facing sites. The beach sand grain sizes ranged from less than 20 µm to over 4000 µm. Eight sites are classified as having very coarse sands, six of which are in the northern part of the atoll. There is no significant correlation (p = 0.18) between the median grain size of the sand particles and the number of plastic particles per kilogram of sand when comparing all 39 sites. Finally, we look at the relationship between sediment grain size and plastic particle size. This study establishes an important baseline for plastic pollution in Tetiaroa Atoll's sandy habitats. This study reveals the widespread presence of plastic particles across its motus and highlights the need to understand plastic distribution and composition for effective conservation and management.