Resolution of matrix effects on analysis of total and methyl mercury in aqueous samples from the Florida Everglades

 Aqueous samples from the Florida Everglades present several problems for the analysis of total mercury (HgT) and methyl mercury (MeHg). Constituents such as dissolved organic carbon (DOC) and sulfide at selected sites present particular challenges due to interferences with standard analytical techniques. This is manifested by 1) the inability to discern when bromine monochloride (BrCl) addition is sufficient for sample oxidation for HgT analysis; and 2) incomplete spike recoveries using the distillation/ethylation technique for MeHg analysis. Here, we suggest ultra-violet (UV) oxidation prior to addition of BrCl to ensure total oxidation of DOC prior to HgT analysis and copper sulfate (CuSO₄) addition to aid in distillation in the presence of sulfide for MeHg analysis. Despite high chloride (Cl^-) levels, we observed no effects on MeHg distillation/ethylation analyses.