Bioaccumulation and toxic effects of nanoparticulate and ionic silver in Saccostrea glomerata (rock oyster)

The increasing production of Ag nanoparticle (AgNP) containing products has inevitably led to a growing concern about their release into the aquatic environment, along with their potential behaviour, toxicity, and bioaccumulation in marine organisms exposed to NPs released from these products. Hence, this study is focused on the effects of AgNPs in Saccostrea glomerata (rock oyster) in artificial seawater (ASW); evaluating the NP's stability, dissolution, and bioaccumulation rate. AgNPs NM300K (20 ± 5 nm) in concentrations of 12.5 μgL^-1 and 125 μgL^-1 were used to conduct the experiments, and were compared to a blank and a positive control of 12.5 μgL^-1 AgNO₃. Dissolution in ASW was measured by ICP-OES and stability was assessed by TEM after 1 h and 3, 5, and 7 days of exposure. Bioaccumulation in gills and digestive glands was measured after 7 days of exposure. The higher concentration of AgNPs induced more aggregation, underwent less dissolution, and showed less bioaccumulation, while the lower concentration showed less aggregation, more dissolution and higher bioaccumulation. Five biomarkers (EROD: ethoxyresorufin-o-deethylase, DNA strand breaks, LPO: lipid peroxidation, GST: glutathione S-transferase and GR: glutathione reductase) were analysed at 0, 3, 5 and 7 days. Significant differences compared to the initial day of exposure (day 0) were reported in DNA strand breaks after 5 and 7 days of exposure, GST, from the third day of exposure, in all the Ag samples, and in some samples for LPO and GR biomarkers, while no significant induction of EROD was observed. A combined effect for each type of treatment and time of exposure was also reported for DNA strand breaks and GST biomarkers measured at the digestive glands. In general, the significant inductions measured showed the following trend: 125 μgL^-1 AgNPs >12.5 μgL^-1 AgNPs ∼12.5 μgL^-1 AgNO₃ even though bioaccumulation followed the opposite trend.