Vulnerability of Tidal Flats to Microplastics in La Parguera, Puerto Rico

Description

To assess microplastics (MPs, <5 mm) distribution within tidal flats we studied four sites in southwest Puerto Rico with varying mangrove densities and anthropogenic influences. We characterized MPs from surface sediments along a transect at each tidal flat. Total microplastics (MPs) collected by site and size and MPs per kg of sediment.

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At low tide on 7 June and 8 June 2023, we placed a 30-m transect beginning at the roots of the mangroves when accessible and ending at the nearest road at each site. Because of the small tidal flat at Site 1, the total transect was 10 m in length. Sediment samples were collected from a 0.15 m2 quadrat using a metal trowel to remove the surface layer (<1 cm deep). Four samples were collected at each site; the first was adjacent to the edge of the mangrove roots at 0 m, and the other three were selected randomly with an online number generator (Table 1). The sixteen samples were air dried for one week, prior to packing and shipping to Villanova University, PA. They were placed in a drying oven at 60◦C for up to 72 hours. Once completely dried, samples were sieved through four incrementally smaller mesh sizes to divide the sediment and marine debris into size categories of macro (>25 mm, sieve size 1), meso (5-25 mm, sieve size 3 ½), and microplastics (<5 mm, sieve sizes 18 and 50). Samples were weighed (g) by size and site, and any plastic pieces were isolated from each sediment grain size fraction using density separation.

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