Mercury Analysis of Acid- and Alkaline-Reduced Biological Samples: Identification ofmeta-Cinnabar as the Major Biotransformed Compound in Algae

Abstract

ABSTRACTThe biotransformation of HgIIin pH-controlled and aerated algal cultures was investigated. Previous researchers have observed losses in Hg detection in vitro with the addition of cysteine under acid reduction conditions in the presence of SnCl2. They proposed that this was the effect of Hg-thiol complexing. The present study found that cysteine-Hg, protein and nonprotein thiol chelates, and nucleoside chelates of Hg were all fully detectable under acid reduction conditions without previous digestion. Furthermore, organic (R-Hg) mercury compounds could not be detected under either the acid or alkaline reduction conditions, and only β-HgS was detected under alkaline and not under acid SnCl2reduction conditions. The blue-green algaLimnothrix planctonicabiotransformed the bulk of HgIIapplied as HgCl2into a form with the analytical properties of β-HgS. Similar results were obtained for the eukaryotic algaSelenastrum minutum. No evidence for the synthesis of organomercurials such as CH3Hg+was obtained from analysis of either airstream or biomass samples under the aerobic conditions of the study. An analytical procedure that involved both acid and alkaline reduction was developed. It provides the first selective method for the determination of β-HgS in biological samples. Under aerobic conditions, HgIIis biotransformed mainly into β-HgS (meta-cinnabar), and this occurs in both prokaryotic and eukaryotic algae. This has important implications with respect to identification of mercury species and cycling in aquatic habitats.