The abundance and localization of environmental microplastics in gastrointestinal tract and muscle of Atlantic killifish (Fundulus heteroclitus): a pilot study

Abstract

Microplastics (MPs) have been found in a diverse range of organisms across trophic levels. While a majority of the information on organismal exposure to plastics in the environment comes from gastrointestinal (GI) data, the prevalence of MP particles in other tissues is not well understood. Additionally, many studies have not been able to detect the smallest, most prevalent, MPs (1 µm - 5 mm) that are the most likely to distribute to tissues in the body. To address these knowledge gaps, MPs in the GI tract and muscle of Atlantic killifish (Fundulus heteroclitus) collected from two sites (Falmouth and Bourne) on Buzzards Bay, Cape Cod, MA were quantified down to 2 µm in size. Eight fish from Falmouth and 10 fish Bourne site were analyzed. Fourier-transform infrared spectroscopy and Raman spectroscopy were used to identify all particles. The mean concentrations of MPs in the GI tract and muscle from fish collected from Falmouth was 85.5 ± 70.2 and 11 ± 12.5 particles per gram wet weight, respectively. Fish collected from Bourne site had mean particle concentrations of 12.2 ± 18.1 and 1.69 ± 5.36 particles per gram wet weight. Of the 2,008 particles analyzed in various fish tissue samples, only 3.4% (69 particles) were identified as plastic; polymers included nylon, polyethylene, polypropylene, and polyurethane. MPs detected in the GI tract samples also tended to be more diverse in both size and polymer type than those found in the muscle. We found that MPs < 50 µm, which are often not analyzed in the literature, were the most common in both the GI tract and muscle samples. There was not a significant correlation between the MP content in the muscle compared to the GI tract, indicating that GI tract MP abundance cannot be used to predict non-GI tract tissue MP content; however, MP abundance in muscle correlated with fish total length, suggesting potential bioaccumulation of these small MPs.

Supplementary information: The online version contains supplementary material available at 10.1186/s43591-024-00101-w.

Keywords: Bioaccumulation; Fish; Fourier-transform infrared spectroscopy; Microplastics; Raman spectroscopy; Translocation.

Fig. 1

Map of Southeastern Massachusetts showing the two collection sites (Falmouth, MA, Bourne, MA). Geographical coordinates and environmental parameters at the collection sites are provided in supplemental information (Table S1)

Fig. 2

Schematic workflow: Illustration of sample processing and analysis of tissue samples using Fourier-transform infrared spectroscopy (FTIR; particles > 25 µm) and Raman spectroscopy (particles 2—25 µm). Data analysis was done by matching the sample spectra to a reference library using OpenSpecy

Fig. 3

Examples of spectra. The r value reflects Pearson’s r correlation for the sample and reference spectra. The reference spectra are shown in black, and the sample spectra are shown in coral. Spectra included in analysis had low background noise and few extraneous peaks. Spectra excluded from analysis due to the large number of non-matching peaks

Fig. 4

Plastic occurrence and concentration in samples: Samples collected in Falmouth are shown in blue, and samples collected in Bourne are shown in green. A Graph showing percentage of samples that were found to contain microplastics for the three sample types studied (water, GI tract, and muscle). Numbers over bars indicate the percentage found. B Box and whisker plot showing the minimum and maximum number of microplastics found per gram of tissue (wet weight). Data were corrected to account for the whole sample based on the observed 8% of the filter that was analyzed. The solid line indicates the median concentration. N = 8 fish from Falmouth and N = 10 fish from Bourne

Fig. 5

Plastic size distribution: GI tract samples shown in brown. Muscle samples shown in tan. A Full size range showing the lengths of microplastics in microns using a logarithmic scale. B Full range of the aspect ratios (length/width) for microplastics using a logarithmic scale. C Percentage of particles in samples classified as fragment (aspect ratio < 2) or fiber (aspect ratio > 2)

Fig. 6

Microplastic Polymer Frequencies: A Total number of microplastics found in the samples color-coded by polymer type. Data were corrected to account for the whole sample based on the observed 8% of the filter that was analyzed. B Percentages of the different polymers present in the GI tract and muscle samples. Data for individual fish can be found in Figure S3 and Supplemental Data File 3

Fig. 7

Relationship between fish total length and microplastic abundance: Scatter plot showing the relationship between the total length of a fish and the number of microplastics present. Data were corrected to account for the whole sample based on the observed 8% of the filter that was analyzed. Data was not normalized by wet weight. The Falmouth samples are shown in blue (n = 8), and the Bourne samples (n = 10) are shown in green. GI tract samples are shown in a darker shade than the muscle samples

Fig. 8

Microplastic Abundance Relationships with Fish Total Length and Sex: Data is corrected to account for the whole sample based on the observed 8% and normalized by tissue wet weight. A-C Linear regression lines with dotted 95% confidence intervals are shown. Correlation refers to the Spearman (nonparametric) correlation analysis between the two variables. A Scatter plot showing the relationship between the total length of a fish and the number of MPs in the GI tract. B Scatter plot showing the relationship between the fish total length and number of MPs in the muscle. C Scatter plot showing the relationship between GI tract MP concentration and Muscle MP concentration. D A box and whisker plot depicting the minimum and maximum concentration of microplastic particles (number of particles/g of tissue w.w.) for the males and females collected. Significance is indicated with an * (p-value < 0.05)