Partitioning of copper at concentrations below the marine water quality criteria

Partitioning of Cu between the aqueous and particulate phases and among their components was examined in six ambient Puget Sound, Washington State, USA, samples (6-10 nM Cu). Most of the particulate Cu (4-12% of the total Cu) was associated with particulate organic matter, and resulted in distribution coefficients (Kd) ranging between 10(4.55) and 10(5.1). For the dissolved phase, the portion of Cu extracted by C18-packed cartridges averaged 44% (+11%). Radioactive 64Cu was added to these samples to total stable Cu concentrations (17-33 nM). After 24 h of equilibration, the portion of 64Cu associated with the particulate matter in five of the six samples (Kd between 10(4.7) and 10(5.3) was an average of 70% higher than that of natural Cu in the ambient samples. In contrast, only 19 +/- 7% of the 64Cu was extracted by C18-packed cartridges. The partitioning of natural Cu and 64Cu onto particles was not significantly different when the equilibria were based on dissolved Cu passing through the C18 cartridges. Further research is warranted on utilizing the hydrophilic component of the dissolved phase as a parameter on which water quality criteria are based.