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Stable Cu isotope(65Cu)was complexed with various representative dissolved organic carbon(DOC)sources,including coastal seawater DOC,fulvic acid(FA),cyanobacteria spirulina(SP)DOC,histidine(His),cysteine(Cys),and lipophilic diethyldithiocarbamate(DDC)at different concentrations.The uptake of these dissolved Cu species by the coastal green mussel Perna viridis was quantified for the first time.All the Cu-DOC complexes were taken up in some measure by the mussels,which is in contrast to general expectations,but complexation generally reduced the Cu uptake as compared to that of the inorganic Cu species.The DOC-type specific Cu uptake was dependent on some key properties of DOC,e.g.,size,concentrations and strong Cu binding sites.Uptake of Cu was higher when complexed with small molecules(e.g.,free amino acids)while lower when complexed with large molecules(e.g.,spirulina proteins).Furthermore,DOC type-specific negative relationships were found between DOC levels and Cu uptake.Strong Cu binding sites(including His and organic sulfur functional groups)within DOC appeared to control the inhibitory effects of DOC on Cu uptake,possibly due to the competitive binding of Cu between the dissolved phase and biological membranes or intracellular Cu binding sites.In addition,strong Cu binding sites may explain the differences in bioavailability of Cu complexed with different types of DOC.Our results highlight the importance of considering the specificity of Cu-DOC complexes when assessing biological exposure to dissolved Cu in natural waters,especially during events,such as phytoplankton bloom periods,that could modify DOC composition and concentrations.