Quantitative Analysis of Selected Plastics in High-Commercial-Value Australian Seafood by Pyrolysis Gas Chromatography Mass Spectrometry

Oysters are deposit feeders, which means that they filter particulate matter (including microplastics) from the water and sediments. The particles are first taken up through the inhalant siphon from the surrounding water and trapped in the gills, which is the first contact organ. In the gills, the particulate matter transfers to the haemolymph that goes to the heart and from there it is distributed to the rest of the body because of oyster’s open circulatory system. Bivalves are usually eaten whole without removal of the digestive tract and hypothetically represent a scenario of microplastic exposure. The European Food Safety Authority (EFSA) reported the possible scenario of ingestion of mussels: after the consumption of 225 g (approximately 10 mussels) and using the highest reported microplastic concentration so far, it would give a total exposure to 900 pieces of plastic. Assuming spherical microplastics with a diameter of 25 μm and density of 0.92 g cm, the exposure would be a total mass of 7 μg per 10 mussels eaten. On the other hand, the latest report of the World Wide Fund (WWF) for Nature (12) states that an average seafood consumer could be ingesting up to 0.5 g of plastic a week, when considering shellfish intake. In 10 oysters analyzed, we had a total plastic concentration of 0.1 mg gtissue. Following the ingestion of 10 oysters, the average mass of plastic intake per serving would be approximately 0.7 mg (depending on the oyster’s weight) ( Table 1 ), which is a much higher value than what the EFSA reports and lower than the WWF one. From all the tested seafood organisms in this study, oysters were expected to have the highest plastic content because of their filter feeding nature and habitat. Furthermore, a recent review suggests that lower trophic organisms, such as bivalves, are at higher risk of contamination of microplastics because, besides their filter feeding nature, the available research data suggest that microplastics do not biomagnify in the food web. (22) Oysters have been widely reported for microplastics contamination. Studies have divulged the presence of microplastics in oysters purchased from farms and local markets. Teng et al. (15) found an average of 0.62 microplastics per gram (wet weight) in farmed oysters from 17 different sites in China. Rochman et al. (19) reported 0.6 ± 0.9 microplastics per individual inpurchased from a market in USA, and Van Cauwenberghe and Janssen (11) found 0.47 particles per gram of tissue in oysters acquired from a supermarket in France. A possible explanation for the “low” plastic content found in the present oysters (at least when compared to what was expected being a filter feeder) can be their source. The oysters in this study originated from the west coast of Australia, where the microplastic content of surface waters is reported to be lower than in other regions of the world such as Asia or Europe. (54,55) A future comparison of the microplastic content by Py-GC/MS analysis among oysters from different geographical locations may help to further elucidate any such differences.