Microplastics in the Delaware Bay: distribution and direct effects on major zooplankton

Microplastic marine debris (MP) is an emerging pollutant of growing concern. Despite the recent surge in MP research, there has been little research to quantify the distribution of microplastic in mid-Atlantic estuaries such as the Delaware Bay, or to study the effects microplastics have on dominant Bay zooplankton. These data are essential for guiding efforts to mitigate and control microplastic pollution in the region. ☐ To quantify the distribution of microplastics, we collected samples from 16 locations across the Delaware Bay ranging from tidal fresh waters near Wilmington, DE to marine waters outside the Bay mouth. Samples were processed through wet peroxide oxidation and manually classified to type (filament, fragment, beads, other) under a dissecting microscope. A 1.8% subset of collected microplastics were then taken from the samples to identify polymer composition using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). In subsequent laboratory experiments, I determined effects of MP exposure at environmentally relevant concentrations on the common calanoid copepods Acartia tonsa and Centropages hamatus, quantifying mortality, growth, development, and respiration through a series of acute and chronic exposures. ☐ Observations in Delaware Bay showed more microplastics in April than June, suggesting seasonal rainfall plays a role in its distribution. More microplastic was found in the Estuarine Turbidity Maximum than other areas, suggesting the importance of hydrodynamics as well as proximity to areas of urban land use in microplastic distribution. Bay samples showed significantly more fragments and filaments than other microplastic types. ATR-FTIR analysis showed most samples were composed of polyethylene and polypropylene with significant association between microplastic type and polymer composition. Most fragments were composed of polyethylene followed by polypropylene while most filaments were composed of polypropylene. ☐ Laboratory exposures of copepods to microplastics showed no significant effect of microbeads on A tonsa survival irrespective of microbead size, concentration, or length of acute exposure (24h or 48h). In chronic developmental experiments, MP exposure decreased body length in C. hamatus NII nauplii across concentrations. Additionally, MP (10 beads L-1) increased respiration rate in mid-copepodites. Despite these two effects, I observed little effect of MP on copepod physiology. Collectively, my work suggests microplastics are present in Delaware Bay, but effects of environmentally relevant concentrations in simplified laboratory conditions are less clear.