The fate of Hg0 in natural waters

Maria Cristina Canela,Wilson F Jardim

doi:10.1590/s0103-50531997000400016

Abstract

Several aspects of the aquatic chemistry of elemental mercury (Hg0) are vital to the understanding of the fate of this metal in the environment, yet have scarcely been studied. Reactive dissolution of metallic mercury is shown to be dependent on the metal concentration in solution, the metal oxidation rate, particulate material concentration, nature and concentration of other ions, and pH. When using 1 g L-1 of Hg0 in distilled water open to the atmosphere, the concentration of soluble mercury increases as a function of time, reaching 5.4 mg L-1 of total Hg in the steady state. From this, 3.2 mg L-1 were due to Hg2+ formed via oxidation. In lake water, results showed an inhibition in the reactive dissolution process, and the total metal concentration in water was 3.1 mg L-1 in the steady state. This inhibitory effect was attributed to particulate material. In seawater, the total concentration of soluble Hg increases as a function of time, reaching a peak of 17.8 mg L-1 after 10 h. After this, the soluble concentration dropped, to 4.8 mg L-1. Experiments performed at different values of pH (4.0;7.0 and 9.0), showed that the dissolution of the metal occurred to a higher extent at pH 4.0. Adsorption studies of both mercuric ions and elemental mercury species onto particulate material showed a dependence on the surface area, following the sequence 400 mesh > 200 mesh > sediment in natura. The implications of such findings are discussed, taking into consideration the Amazonian scenario.

Highlights

Predicting the real impact related to emissions of mercury into the environment still poses many problems, since some of the fundamental aspects of the aquatic chemistry of mercury have not yet been fully studied
The first attempt to estimate the solubility of Hg0 in water was done by Bonhoelfer and Reichardt[15], where the authors showed the existence of the species Hg0(aq) using the resonance line of mercury at 253.7 nm
The solubility of elemental mercury in water has been studied by many other researchers and, except for the fact that the concentration of Hg0 has varied from 100 g L-1 14,16,17 down to 22 g L-1 18, the common feature in all these studies is the absence of dissolved oxygen and presence of a reducing agent to avoid the formation of the Hg2+ species in a closed system

Summary

Introduction

Predicting the real impact related to emissions of mercury into the environment still poses many problems, since some of the fundamental aspects of the aquatic chemistry of mercury have not yet been fully studied. When using 1 g L-1 of Hg0 in distilled water open to the atmosphere, the concentration of soluble mercury increases as a function of time, reaching 5.4 μg L-1 of total Hg in the steady state.

Results

Conclusion