Translocation of microplastic in the circulatory system of the oyster Crassostrea gigas : Evidences and uncertainties :investigation to load.

The oyster Crassostrea gigas, is likely to be impacted by microplastic (MP) pollution since, as a filter feeder organism, it filters large volumes of water and by the way, it can ingest little particles while feeding. Previous works evidenced the absorption of MP in various tissues of the mouse (Ebel, 1990) using similar techniques as the ones described in the present work. Translocation in the circulatory system (hemolymph) of mussels has also been proposed more recently (Browne et al, 2008). During an experiment where adult oysters Crassostrea gigas were exposed to microplastics (fluorescent beads of 2 and 6 microns), we tested two different methods for collecting hemolymph: in the adductor muscle or directly in the pericardial cavity. We were able to find MPs in the hemolymph of bivalves throughout the experiment. But, did we observed a real translocation phenomenon or was it a simple contamination due to sampling technique? The presence of MPs in the water of the pallial cavity, three days after stopping the exposure, casts doubt on the reality of the phenomenon of translocation. The study of histological sections did not raise this doubt, since the presence of microplastic was clearly observed only in the digestive tract.
In view of these results and knowing that it is impossible to exclude completely contamination as an explanation of the observation of MP in the hemolymph in our experiment, we went back to the two papers mentioned above to redo a critical reading: some elements of the methods developed by these authors suggest that there is indeed still some uncertainties as to the reality of the phenomenon of translocation of MP in bivalves. Note that this replay has been deliberately made to load. The aim is to launch the discussion in order to improve our understanding of MP translocation, and to go further on the significance of this phenomena for the physiology of marine animals, especially filter-feeders.