Molecular impacts of dietary exposure to nanoplastics combined with arsenic in Canadian oysters (Crassostrea virginica) and bioaccumulation comparison with Caribbean oysters (Isognomon alatus)

Despite the urge need to address the possible impact of plastic debris, up to now, little is known about the translocation of nanoplastics through the trophic web. Plus, due to their surface reactivity, nanoplastics could sorb and thus increase metals bioavailability to aquatic filter-feeding organisms (e.g., bivalves). In this study, we investigated the dietary exposure route on the oyster Crassostrea virginica through microalgae themselves exposed to three nanoplastic dispersions (PSL, PSC and NPG) at reportedly environmental concentrations combined or not with arsenic. Interactive effects of nanoplastics on arsenic bioaccumulation were studied, along with the expression of key genes in gills and visceral mass. The investigated gene functions were endocytosis (cltc), oxidative stress (gapdh, sod3, cat), mitochondrial metabolism (12S), cell cycle regulation (gadd45, p53), apoptosis (bax, bcl-2), detoxification (cyp1a, mdr, mt), and energy storage (vit). Results showcased that nanoplastic treatments combined with arsenic triggered synergetic effects on gene expressions. Relative mRNA level of 12S significantly increased at 10 and 100 μg L^-1 for NPG combined with arsenic and for PSC combined with arsenic. Relative mRNA level of bax increased for PSL combined with arsenic and for PSC combined with arsenic at 10 and 100 μg L^-1 respectively. We also observed that relative arsenic bioaccumulation was significantly higher in Crassostrea virginica gills compared to Isognomon alatus'. These results are the first comparative molecular effects of nanoplastics alone and combined with arsenic investigated in farmed C. virginica oysters. Together with I. alatus results we thus shed light on species different sensitivity.