CHANGES OF MERCURY CONCENTRATION IN RESPONSE TO CHLORIDE COMPLEX UNDER DEICING SALT CONDITION

Our previous study indicated that Hg concentrations in the stream water of a studied New Jersey watershed, even though low, are significantly correlated with those of Na and Cl. The correlation coefficient between Hg and Na concentrations can be as high as 0.66 (t=3.56, n=18) in the studied watershed. Examination of the published data from a coastal aquifer between the concentrations of Cl and Hg also indicates that high Cl concentration can affect the Hg concentration (correlation=0.88, t=7.78, n=18) when sources of Hg are available. A lack of significant correlation between Hg and Si in our previous studies, on the other hand, indicates that the dominant source of Hg in the stream water is anthropogenic rather than natural in this New Jersey watershed. Hg exists in water as Hg^o, or Hg²⁺, and Hg₂²⁺ and has a strong tendency to form complexes with Cl^- and OH^-containing functional groups of organic ligands, particularly, in a surface water body or shallow ground water. Cl forms hydroxide complexes with Hg²⁺ when the Cl^- concentration is above 10^-9 mol/l. Cl has been regarded as one of the most mobile and persistent complexing agent for Hg. Since the solubilities of HgCl₂ and Hg(OH)₂ are rather high, the affinity of Hg to these ligands leads to an increased mobility of Hg. Our current laboratory study in which powders of Hg mineral are added into the various concentrations of chloride solution is expecting to further quantify the changes of Hg concentration in response to the increased level of Cl in a water body. In addition, examinations of Hg concentration in a lake water body where stratification due to potentially increased NaCl concentration from deicing salt after snow storm will be studied as well. Increased Cl concentration in a water system has been considered to increase desorption and mobilization of Hg from the soil mineral, the organic matter, and the coastal aquifer. Studies of the interaction between Cl and Hg in a water system will help us better understand the effect of the ongoing exploitation of groundwater, the rising sea level along the coast and the increased application of road salt on the formation of HgCl_n complexes, therefore, potential detrimental effect of Hg in a water system.