Marine debris in Charleston Harbor: Characterizing plastic particles in the field and assessing their effects on juvenile clams (Mercenaria mercenaria)
Plastic pollution is widespread at both the macro and micro levels. While past research focused on the distribution and abundance of plastic debris on ocean front beaches, few studies documented the distribution in estuarine harbors. To characterize plastic pollution in Charleston Harbor, we sorted, counted, and weighed all macroplastic debris items collected by local volunteers at eight locations around Charleston Harbor during Beach Sweep in September, 2013. The most common plastic items collected in the Harbor (by number of items) were polypropylene (0.26 items m<sup>−1</sup>) which includes bottle caps and candy wrappers. The most common plastic items by weight were polyethylene terephthalate (3.43 g m<sup>−1</sup>) which includes beverage bottles. Microplastic particles were sampled at the low intertidal, high intertidal, high tide line and supralittoral zone across three transects on three beaches around Charleston Harbor by density separation. Plastic fragments were most abundant at Daniel Island with an average of 1195 items m<sup>–2</sup> across all transects. Fragments at all locations were predominantly black. These black fragments were positively identified as nylon, polyester, and polypropylene using FTIR analysis. To assess the potential toxicological consequences of microplastic debris on juvenile clams, polyethylene microbeads (10–20 µm) were fed to juvenile clams (1–2 mm) in a 21 day chronic exposure and a 24–48 h acute exposure to measure bead uptake. Clams at the highest treatment level grew less than clams in the control. This study suggests that plastic debris may be a potential hazard to clams and other important ecological species in Charleston Harbor.