Determination of the mercury complexation capacity of natural waters by anodic stripping voltammetry

The complexation of mercury by dissolved organic matter (DOM) in natural waters was investigated using Osteryoung square wave anodic stripping voltammetry (OSWASV). The method employed a gold disc electrode and utilised medium exchange (0.1 M perchloric acid/2.5 mM hydrochloric acid) to avoid interferences during the stripping step. The limit of detection (3σ) was 0.11 nM (22 ng l−1) and the relative standard deviation at a mercury concentration of 5.0 nM was 2.8%. Mercury complexation capacities were determined on a range of fresh and saline water samples. In all samples, ligand concentrations were greatly in excess of dissolved mercury concentrations and ranged from 1.35 to 4.47 nM. Log conditional stability constants of the mercury-DOM complexes were in the range 9.7–10.8. The results suggest that the speciation of mercury in natural waters is dominated by complexation with natural organic matter.