Sediment Trap Development and Quantification of Microplastics Deposition in the Black and Waccamaw River Systems, South Carolina

Plastic pollution is a growing environmental concern because of the widespread and toxic damage it can have on ecosystems and the organisms that inhabit them. Microplastics are small plastic particles produced from the degradation of larger plastic items. To better understand the impact of land use on microplastic concentrations in coastal South Carolina rivers, sampling stations were established in a high population density watershed (Waccamaw River) and a low population density watershed (Black River). Two cost-efficient sediment traps were designed; a sediment tile with a koi pond filter attached to a ceramic tile and a pipe cradle installed vertically near the river bottom. Each trap design was deployed in two-month rotations at the two sampling locations, one in the Waccamaw River and one at the Black River. Once collected, the samples were washed, and plastics were separated by density using a 30% calcium chloride solution of density 1.30-1.35 g/ml. Microplastics were removed from the dried samples under a microscope using forceps, counted, and stored in glass vials. To compare sites, microplastic counts were normalized to the number of days the trap was deployed. For the Black River (low population density site), an average of 2.01 plastics/day were found compared to the Waccamaw River (high population density site) average of 2.37 plastics/day. An independent samples t-test found these averages are not statistically significantly different (p = 0.340). It is possible a difference was not detected because of the small number of samples collected; additional samples could result in a significant difference between the observed number of plastics in both rivers. The results of this research will strengthen proper collection methods for microplastics and contribute to the understanding of the dynamics of microplastic deposition in coastal watersheds.