US EPA

1378268 

Technical Report 

Chemistry and Transformations of Mercury and Arsenic in Anaerobic Sediments 

Morel, FM 

1996 

NTIS/02991832 

GRA and I 

GRA and I 

The objectives of this project are to elucidate the chemical and biological mechanisms that control the precipitation and dissolution of arsenic and mercury in anaerobic coastal sediments and to quantify the consequences of these processes in determining the potential release of these toxic elements to the water column and their accumulation in marine organisms. Based on the preliminary research described in the proposal, rapid progress has been made on both the arsenic and the mercury aspects of this project. In particular, the conditions for the microbial reduction of arsenate to arsenite and the precipitation of arsenite as the arsenic trisulfide solid have been documented. These two processes (reduction of arsenate and precipitation of arsenite) largely determine the environmental mobility of arsenic in anaerobic sediments. The rate of dissolution of mercuric sulfide under various conditions and the rates of oxidation and reduction of dissolved mercury are also being quantified. In addition, according to preliminary data, it appears that, as hypothesized in the proposal, the presence of polysulfides can enhance many fold the rate of microbial methylation of mercury in anaerobic sediments. p1. 

Water pollution; *Toxicity; *Marine biology; *Mercury compounds; *Arsenic; *Sediments; *Anaerobic processes; Coastal regions; Chemical reactions; Precipitation; Oxidation; Polysulfides; Aquatic organisms; Dissolving; Microorganisms; Methylation; Arsenic sulfides; Arsenates; Anaerobic coastal sediments; Arsenites; Bioaccumulation