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Microplastic contamination in Corpus Christi Bay blue crabs, Callinectes sapidus

Citation

Waddell, Elijah N.; Conkle, Jeremy L.; Lascelles, Nigel (2020), Microplastic contamination in Corpus Christi Bay blue crabs, Callinectes sapidus, Dryad, Dataset, https://doi.org/10.5061/dryad.mpg4f4qtr

Abstract

Microplastic pollution has been observed in marine environments around the world and has the potential to negatively impact marine organisms when ingested. One organism of particular concern is the blue crab, Callinectes sapidus, whose feeding strategies increase their likelihood of exposure to plastic pollution. To assess microplastic contamination in blue crabs, 39 individuals were collected from Corpus Christi Bay, TX and processed using a hydrogen-peroxide based tissue destruction method followed by confirmation using micro-attenuated total reflectance Fourier transform infrared spectroscopy (µ-FTIR). From the 39 blue crabs sampled, 28 fully synthetic fragments and fibers and 24 semi-synthetic fibers were found within their stomachs. After correcting for possible contamination, 36% of collected blue crabs were estimated to contain 20 synthetic fragments and fibers and 14 semi-synthetic fibers (0.87 items crab-1). This study shows that blue crabs ingest microplastic items in Corpus Christi, TX and populations in other locations likely face similar risks.

Methods

Microplastic ingestion by blue crabs was assessed by collecting specimens from three sites around Corpus Christi Bay. A total of 39 blue crabs were collected (12 from Site A, 15 from Site B, and 12 from Site C) using lines baited with raw chicken. Blue crabs were transported to the lab in a hard-plastic cooler with a polyethylene exterior and polypropylene interior. Travel time from the sampling location to the lab varied from 15-45 minutes.  Upon returning to the lab, the length, mass, and sex of the crabs were recorded. Blue crabs were then chilled to numb their senses and euthanized humanely before their stomachs were collected and individually placed into clean 15 ml scintillation vials. 

Blue crab stomachs were isolated and placed in a clean 50 mL centrifuge tube, loosely sealed with a cap, and dried at 40 °C for 7 days. Then the stomachs were gently crushed with a glass stirring rod to increase the tissue surface area. To ensure no materials remained on the rod, it was rinsed three times into the centrifuge tube with 2 mL of 30 % H2O2, for a total of 6 mL. The glass stirring rod was then visually inspected under a stereomicroscope to ensure no materials remained attached. Samples were then loosely recapped and digested overnight at 20 °C before the addition of another 2 mL of 30 % H2O2 followed by gentle swirling for 15 seconds. This digestion step was repeated twice, using a total of 6 mL more over 72 hours, before the centrifuge tubes digested at 20 °C for a final 48 hours. Next, the centrifuge tubes were heated at 40 °C in a hot water bath for 2 hours before vacuum filtration through a 0.8 µm cellulose acetate membrane filter. The filtering apparatus and now-empty centrifuge tube were inspected under a microscope to ensure the complete transfer of material. Filters were then visually inspected under a stereomicroscope for suspected microplastic materials.

Suspected microplastic particles and fibers extracted from blue crabs were analyzed using µ-FTIR on a Thermo Nicolet iS10 FTIR equipped with a mercury cadmium telluride infra-red detector and a iN5 Microscope with a germanium crystal for attenuated total reflectance. Sample spectra were collected with 256 scans at a resolution of 8 cm -1 over the range of 650 - 4000 cm-1. Backgrounds were collected before each sample run and all collected spectra were compared to the “Forensic Comprehensive”, “HR sprouse polymers by ATR”, “ICHEM Nicodom ATR, ATR 100 Specta Dema Library”, and “Hummel polymer sample library” databases for identification. Samples that positively matched the database (>65% confidence) were included in the results.

All glassware and utensils were washed with detergent and subsequently  rinsed with DI water prior to use. Glassware was muffled at 500 °C for 4 hours and covered with aluminum foil after cooling. Utensils and glassware were inspected under a microscope prior to use. Laboratory contamination of samples was assessed by running a method blank, a pre-cleaned empty vial that was identically processed alongside the samples at a rate of one for every three samples. Each blank was exposed to the same conditions and manipulation as its paired samples, and was, once processed and filtered, left open for the duration of the microscope analysis of the paired samples to assess the possible contamination during this step. In this way, the method blanks were exposed to the same laboratory conditions for the same duration as the three samples they were paired with.  Sample contamination from laboratory sources was assessed by establishing limits of detection (LOD), which is the mean plastic contamination from sample blanks + 3× Standard deviation, for each type of plastic (based on coloration, shape, and material) observed in these method blanks (De Witte et al., 2014).

Usage Notes

Table 1, tab 1 of  the spreadsheet 'Compiled dataset of microplastics and fibers recovered from Corpus Christi blue crabs', describes the physical features (fiber, fragmnet, or film) and coloration of items suspected to be synthetic fibers, fragments, or films as observed in the processed blue crab stomachs. Items detailed in table 1 are considered "suspected" plastics as no identification via FTIR had yet to be performed.

Table 2, tab 2 of  the spreadsheet 'Compiled dataset of microplastics and fibers recovered from Corpus Christi blue crabs', describes the physical features (fiber, fragment, or film) and coloration of items confirmed via micro-FTIR to be plastic or sem-synthetic as observed in the processed blue crab stomachs.

Table 3, tab 3 of  the spreadsheet 'Compiled dataset of microplastics and fibers recovered from Corpus Christi blue crabs', describes the composition of plastic or semi-synthetic items recovered from blue crab stomachs.

Funding

PADI FOUNDATION, Award: 2016 Recipient

National Oceanic and Atmospheric Administration, Award: A16SEC4810009