Variability of microplastics in estuarine systems and consequences for organism studies

Marine micro-plastic (particles smaller than 5 mm in length) pollution is a recently recognized, and growing, threat to the environment. Thus, scientific and public interest in the issue is high and growing. Estimates of microplastic particle numbers are in the tens of trillions worldwide and are sparsely sampled in many ecosystems. A primary challenge in mapping microplastic concentrations is collecting and processing samples in a manner that minimizes contamination, and in collecting enough samples to obtain statistically-relevant data. The challenge is especially acute in coastal ecosystems, where the interplay between human activities, tides, currents and ecosystems makes for a very heterogeneous distribution of microplastics. Our initial efforts in mapping microplastics in Georgia’s intercoastal estuaries indicate the presence of a trillion or more microplastic particles in the region, primarily of the micro fiber category. And these microplastics are transferred to estuarine organisms: 20% to 50% of all fish, crustaceans and shellfish examined contained microplastics within their digestive tracts. However, spatial heterogeneity was high in both water samples and in organisms. Additional temporal sampling of estuaries indicates a high level of heterogeneity in this dimension. The data suggests rapid cycling (input/removal) from this ecosystem, which further suggests that the primary source for these contaminants is local. Limited riverine sampling from the Savannah, Ogeechee, Satilla and Altamaha Rivers supports this hypothesis as well. The large degree of microplastic spatial and temporal heterogeneity in this ecosystem suggests that spot sampling efforts will likely not provide accurate estimates of contamination levels in similar aquatic systems.