Microparticles in fish muscle and gastrointestinal samples from Sarasota Bay, FL

Microplastics have been found in the gastrointestinal (GI) fluid of bottlenose dolphins (Tursiops truncatus), inhabiting Sarasota Bay, FL, suggesting exposure by ingestion, possibly via contaminated fish. To better understand the potential for trophic transfer, muscle and GI tissues from 11 species of dolphin prey fish collected from Sarasota Bay were screened for microplastics (particles <5mm diameter). Suspected microplastics were found in 82% of muscle samples (n=89), and 97% of GI samples (n=86). Particle abundance and shapes varied by species (p<0.05) and foraging habit (omnivore vs. carnivore, p<0.05). Pinfish (Lagodon rhomboides) had the highest particle abundance for both tissue types (muscle: 0.38 particles/g; GI: 15.20 particles/g), which has implications for dolphins as they are a common prey item. Findings from this study support research demonstrating the ubiquity of estuarine plastic contamination and underscore the risks of ingestion exposure for wildlife and potentially seafood consumers.

Methods
Fish were dissected on metal trays using stainless steel scalpels and forceps. Muscle tissue was extracted through a lateral incision extending from the gill slits to the caudal fin, followed by descaling. After removing the filets, the GI tissue was isolated by severing the esophagus and the most posterior section of the intestines. Muscle and GI tissues were digested using a 10% potassium hydroxide (KOH) solution at 60 °C for 24-72 hours to dissolve all organic material. The resulting digestate was vacuum filtered onto a GF/A 1.6 μm glass fiber filter within a fume hood. Samples containing large quantities of inorganic solids or durable organic remnants (i.e., sediment, crustacean exoskeletons, bone, and scales) were pre-filtered through 63 μm and 500 μm sieves prior to vacuum filtration. Filters were then placed in covered petri dishes and stored in a cabinet to dry. Suspected microplastics were visually identified under a Leica EZ4 microscope at 16-35x magnification. Characteristics of suspected microplastics included homogenous coloring, absence of organic or cellular structures, and uniform thickness of fibrous particles. Suspected microplastics were categorized by color and shape. Plastic testing was conducted with a heated (250 °C) soldering needle, which causes plastic particles to bend or melt, as most polymers melt near a temperature of 250°C.