Approved Abstracts

A multi-scale approach for time-course localization of microplastics in target organs of two marine organisms



Author(s): Calmao M; García-Velasco N; Benito A; Thoppil R; Torre-Fdez i; Castro K; Izagirre U; Soto M;
Presenter: Manu Soto

The vast majority of the plastic waste produced in the last century is accumulated in the environment, leading to an exacerbated contamination of marine environments due to transport from land to the ocean. Once in the ocean, and through mechanical abrasion, oxidation, and photodegradation, large plastics degrade to microplastics (MPs), plastic pieces with different shapes between 0.1 µm – 5mm (European Food Safety Authority, 2016). MPs are widely transported through water currents throughout the marine environment reaching the water surface, water column and sediments. Hence, they have become widespread contaminants of emerging concern in the marine environment since they can be accumulated by aquatic species, entering the trophic chain and becoming a potential threat to humans. Therefore, in the present research, we aimed to decipher the transport and distribution time-courses between different organs of sentinel aquatic organisms. Fluorescent polystyrene microplastics of 1µm were used to ease the anatomic tracking in two marine organisms placed in a microcosm: the mussel Mytilus galloprovincialis and the polychaete Hediste diversicolor. Experimental tanks were filled with a clean sediment layer (6 cm, collected in a clean/reference place -Plentzia-) and 3 L of filtered seawater, obtaining a sediment/seawater depth ratio of 1:3. MPs were spiked into the overlying seawater for the exposure, creating three experimental groups: control, low dose (103 particles/mL), and high dose (105 particles/mL). In each container, 6 mussels and 5 ragworms were caged in a net and introduced into the sediment, respectively. Exposures were performed with the absence of food, persistent aeration, controlled temperature of 18 ºC, and a 12/12 h photoperiod. Organisms were collected at different exposure times (1 hour, 4 hours, 24 hours, and 72 hours), dissected out, frozen in liquid nitrogen and stored at -40ºC for further histology. Three different anatomical parts of the body were selected and processed for the polychaetes: hindgut, midgut, and foregut. In mussels, cross-sections of the whole animal and also individualized digestive gland and gills were obtained. Cryofixed samples were sectioned through cryostat at a chamber temperature of -25ºC with a thickness of 20 µm and analyzed under a fluorescent microscope (excitation: 482/35 nm). As expected, no fluorescent MPs were detected in ragworms tissues. Nevertheless, in mussels exposed to low and high doses of MPs, particles were found in distinct parts of the digestive tract (stomach, digestive diverticula, gastrointestinal segments) and gills. Even if the majority of the MPs were localized in the lumen of the digestive tract, in some cases, they were detected inside the digestive epithelium (i.e. digestive cells). TThe identification of MPs and their internalization in the digestive system was confirmed using Raman microscopy. The obtained data reveal a trend of decrease in MPs number in the digestive tract (mainly in the stomach) of mussels with time, being more noticeable when comparing mussels exposed to MPs for short times (1h, 4 h) with longer times (24 h, 72 h). Thus, the histology with frozen sections, together with Raman microscopy, appeared to be an accurate methodology for detecting MPs in tissues and revealing their presence in different structures of the digestive tract of mussel. This work contributes to understand the distribution, fate, and impact of MPs in the food chain in the real environment. Acknowledgement: MINECO (PLASTeMER, Retos 2020); Basque Government (ELKARTEK 2021-2022), Basque Gov. (IT1302-19).

Keywords: microplastics; multispecies microcosm; localization

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