Polystyrene microplastic contamination versus microplankton abundances in two lagoons of the Florida Keys

Abstract

A microscopic study of microplankton in two coastal lagoons in the Florida Keys coincidently, and unexpectedly, revealed the widespread presence of high concentrations of polystyrene microplastic particles. The polystyrene particles were first observed in the second year of a 2-year study of phytoplankton communities, with peak densities in the spring/summer of 2019 at all ten sampling sites in the two lagoons. Polystyrene particle densities reached levels up to 76,000 L^-1. The particles ranged in size from 33 to 190 µm, similar to the size range of microplanktonic algae (20-200 µm). Over the period of peak polystyrene densities, average particle densities were similar to average densities of microplanktonic algae cells. The latter observation highlights the potential significance of the microplastic particles for the ecology of the pristine waters of the Florida Keys, if they persist.

Figure 1

Map of sample regions and study sites (map was based on ArcMap Version 10.7 base image).

Figure 2

Microscopic image (×400 magnification) of a Pyrodinium bahamense cell and polystyrene particle in water sample (a—top panel), and microscopic image (×100 magnification) of a broader view of multiple polystyrene particles including the dinoflagellate Tripos hircus. Arrows indicate the location of polystyrene particles (b—bottom panel).

Figure 3

Baseline-corrected FT-IR spectrum of microplastic particle in water samples (top panel) particle and comparison reference spectra for standard forms of polystyrenes (the most common commercial forms). The percentage match for the three reference forms were: (1) 95.15% for Polystyrene Standard, typical MW 200.000 (HR Aldrich FT-IR Collection 1, (2) 91.40% for Polystyrene Standard, typical MW 50.000 (HR Aldrich FT-IR Collection 1, and (3) 90.36% for Polystyrene Atactic (Hummel Polymer Sample Library).

Figure 4

Frequency of observation of different size classes of polystyrene microplastics observed from 100 randomly selected particles over the study period.

Figure 5

Concentrations of polystyrene microplastic particles at five sampling sites in Barnes Sound (1–5) and five sites in northeast Florida Bay (6–10) from January 2019 to March 2020.

Figure 6

Salinities at Site 1 in Barnes Sound and Site 9 in N.E. Florida Bay from January 2019 through March 2020.

Figure 7

Examples of composition of microplanktonic phytoplankton (i.e. 20–200 µm) in Barnes Sound and NE Florida Bay in terms of cell density over the period when polystyrene microplastic particles were observed, i.e. January 2019 to March 2020.