Speciation analysis of mercury in river water in West Java, Indonesia

Abstract

Mercury speciation was studied in the Cikaniki and Cidikit rivers, both of which have been contaminated by mercury as a consequence of gold mining. Sampling was carried out in October 2001 and in September 2002. It is well known that humic acid has the ability to bind metal ions, an environmentally important aspect because complex formation might change the toxicity and movement of mercury.High concentrations of mercury were found in suspended particles at all sampling sites. Scanning Electro Microscope (SEM) images of suspended particles and elemental analysis data by X-Ray spectroscopy showed that the suspended particles were a clay-like mineral. Cationic and anionic species of mercury were also found in the water samples but at relatively low concentrations. Since the presence of humic acid was observed in the river water, the anionic species of mercury seemed to be a complex of mercury with humic acid. The total mercury concentration in the Cikaniki River was higher than the maximum tolerable concentration (0.002 mg ⁄ l) allowed for river water by Indonesian Government regulations. In the Cidikit River, the concentration of mercury was less than the maximum tolerable concentration for river water. Humic acid concentration was also measured to reveal the relationship between the distribution of mercury and humic acid; however, this relation is still unclear.In the laboratory, the conditional stability constant and capacity of humic acid and mercury to form complex were estimated by Scatchard plot, at pH 6, using a 5 mg ⁄ l humic acid and mercury (II) solution in concentration range of 0-0.6 μM. The value of conditional stability constant between mercury (II) and humic acids is log K’= 6.5 at pH 6 and the complexing capacity of mercury (II) is 0.38 μM.