Subcellular controls of silver biokinetics in the green mussel Perna viridis from two hydrographic zones

The roles of subcellular distribution on silver (Ag) accumulation and elimination in the green mussel Perna viridis collected from 2 hydrographical zones (harbour vs. estuarine) in Hong Kong during 3 different seasons were investigated. Ag concentration and biokinetics varied widely between the 2 zones, but were less variable among the different seasons (pre-wet, wet and dry). The harbour population had a 2to 6-fold higher Ag tissue concentration than the estuarine population. The insoluble fraction was the predominant pool for Ag subcellular distribution in the green mussels. In both the pre-wet and wet seasons, a lower Ag tissue concentration was associated with the insoluble fraction in the estuarine population as compared to the harbour population. Ag uptake from the aqueous phase was faster in the estuarine population during all seasons, but no significant relationship between Ag uptake and salinity was found in this study. Dietary uptake of Ag was similar in both populations, although there was a slight difference in assimilation from diatoms and natural seston. Efflux of Ag was 2 times faster in the estuarine population during the wet and dry seasons, which may partially explain the lower Ag tissue burden in the mussels. These results demonstrated a close correlation between Ag kinetics and its subcellular distribution. The percentage of Ag in the heatsensitive proteins correlated positively to the influx of dissolved Ag and Ag efflux, but negatively to the dietary assimilation. On the other hand, a higher percentage of Ag in the insoluble fraction was related to a higher dissolved uptake rate constant and a lower assimilation. Thus, the role of the individual subcellular fraction in the uptake was exposure pathway-specific. This study highlights the importance of subcellular Ag partitioning in controlling its accumulation and detoxification in bivalves.