Screening of Microplastics in Aquaculture Systems (Fish, Mussel, and Water Samples) by FTIR, Scanning Electron Microscopy–Energy Dispersive Spectroscopy and Micro-Raman Spectroscopies

Abstract

In the last decade, plastic waste has become one of the main threats to marine ecosystems and their biodiversity due to its abundance and increased persistence. Microplastics can be classified as either primary, i.e., fabricated for commercial use, or secondary, i.e., resulting from the fragmentation/weathering processes of larger plastic pieces in the environment. In general, microplastics are detected in a number of aquatic organisms (e.g., fish, bivalves, mollusks, etc.) with alarming effects on their health. Therefore, the present work focuses on the detection and identification of microplastics in fish species (Dicentrarchus labrax, Sparus aurata) and mussels (Mytilus galloprovincialis) from aquaculture systems since these aquatic organisms are largely commercially available for consumption. In addition, seawater was also screened for the types of polymers present as well as their aging. The experimental protocol for biota samples contains a digestion step using Fenton’s reagent (0.05 M FeSO4⋅7H2O with 30% H2O2 at a volume ratio of 1:1) to remove organic material followed by filtration and a density separation step where the sample material was mixed with a saturated ZnCl2 solution to separate microplastic particles from heavier material. For seawater samples (sampled by a microplastic net sampler), only sieving on stainless steel sieves followed by filtration on silica filters was applied. Detection of microplastics and identification of their polymeric composition was achieved through the combined use of micro-Raman analysis, Attenuated Total Reflectance–Fourier Transform Infrared spectroscopy, and Scanning Electron Microscopy in tandem with Energy Dispersive X-ray spectroscopy. Microplastic abundance was 16 ± 1.7 items/individual in mussels and 22 ± 2.1 items/individual in sea bass, and 40 ± 3.9 items/individual in sea bream, with polyethylene (74.4%) being the most detected polymer type, while polyethylene-co-vinyl acetate (65%), polyvinyl-butyral (36.8%), polyvinyl alcohol (20%), and polybutyl methacrylate (15.8%) were also detected to a lesser extent. The microplastics isolated from seawater samples were films (30%), fragments (30%), and fibers (20%), while some of them were derived from foams (20%). Also, in most of these seawater-recovered microplastics, a relatively high degree of oxidation (carbonyl index > 0.31) was observed, which was further confirmed by the results of Energy Dispersive X-ray spectroscopy. Finally, the Scanning Electron Microscopy images showed various morphological characteristics (cracks, cavities, and burrs) on the surfaces of the microplastics, which were attributed to environmental exposure.

Microplastics in Mediterranean Mussel Mytilus galloprovincialis: Comparison between Cultured and WildType Mussels from the Northern Adriatic

“…The results from a study conducted by Vasanthni et al have confirmed that fibers were the predominant type of MPs observed in the mussel P. viridis from Kasimedu, Chennai, India, followed by spheres, flakes, sheets, and fragments [67]. Furthermore, in a study conducted by Gündo gdu et al, the MPs found in mussels bought at the Turkish market in five different cities were identified as fibers (62.7%) and fragments (37.3%) [94]. Fragments or fibers were also mainly recorded as the dominant shape of MPs found in the edible green-lipped mussel P. viridis by using an automated mapping technique of Raman microspectroscopy [97].…”

“…These elements are characteristic of different types of plastics, can be detected using methods such as SEM-EDS, were identified as MPs (Figure 4a), and were included in further data analysis. On the contrary, a particle that consisted of a larger portion of oxygen and silicon atoms was identified as a mineral particle (Figure 4b) and was not taken into account, as was found in many studies [32,51,[93][94][95]. Analyzing cryosections of a mussel's digestive gland with SEM-EDS could offer a good way to perform detection.…”

“…The total number of identified MPs per mussel digestive gland is shown in Figure 5. particle (Figure 4b) and was not taken into account, as was found in many studies [32,51,[93][94][95]. Analyzing cryosections of a mussel's digestive gland with SEM-EDS could offer a good way to perform detection.…”

“…For instance, Vandeermersch et al have found an average of 0.18 ± 0.14 items/g of wet weight for the acid mix method and 0.12 ± 0.04 total items/g of wet weight using the nitric acid method in the field-collected mussels M. galloprovincialis from three different "hotspot" locations in Europe (Po estuary, Italy; Tagus estuary, Portugal; Ebro estuary, Spain) [79]. The average amount of MPs found in mussels sold on the market in five Turkish cities was determined to be 0.6 ± 0.1 MPs/mussel using chemical digestion and, further, µ-Raman spectroscopy [94]. Furthermore, the presence of MPs recorded in two commercially grown bivalves Mytilus edulis and Crassostrea gigas was found to be 0.36 ± 0.07 particles/g w/w and 0.47 ± 0.16 particles/g w/w, respectively [89].…”

Assessing Microplastics and Nanoparticles in the Surface Seawater of Venice Lagoon—Part I: Methodology of Research

“…Multiple analytical techniques based on mass or particle size determinations are usually required to obtain information about the concentration, chemical composition, and shape of MPs and NPs. MP identification techniques include microscopic observations [36], µ-Raman [37,38], Fourier transform infrared spectroscopy (FTIR) [38,39], µ-FTIR [31], scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDX) [36,38], and micro-optofluidic platform [36,40], while the NPs have been evaluated using thermal desorption-proton transfer reaction-mass spectrometry (TD-PTR-MS) [29,41], dynamic light scattering (DLS) [26,42,43], transmission electron microscopy (TEM) [44,45], surface-enhanced Raman spectroscopy (SERS) [46], and pyrolysis-gas chromatography/mass spectrometry Py-GC/MS analytical techniques [47]. Since no single analytical method is able to obtain the physical (size, shape, and color) and chemical (polymer type) characteristics of MPs in a single step, the combination of several parallel approaches should be applied and considered.…”