Poster: Phytoremediation

Abs # 983: Biotransformation of Hg²⁺ by selected cyanobacteria.

Presenter:	Lefebvre, Daniel D., lefebvre@biology.queensu.ca
Authors	Lefebvre, Daniel D. (A)   Kelly, David  (A)   Budd, Kenneth  (A)
Affiliations:	(A): Dept. Biology, Queen's University

The biotransformation of Hg²⁺ by selected cyanobacteria was investigated under pH-stat culture conditions at environmentally relevant Hg²⁺:chl a ratios. A novel method permitted the selective, quantitative determination of b-HgS. A direct, simultaneous determination of this pathway together with losses to the well-known reductive Hg° pathway was made, thereby assessing the fate of Hg²⁺ doses in real time. Upon exposure of cyanobacteria to Hg²⁺, acid SnCl₂ reducible Hg signal (free ions and complexes) was transformed to alkaline SnCl₂ reducible Hg signal consistent with b-HgS and inconsistent with other biologically-reported mercury compounds and complexes. The initial biotransformation process included a rapid phase for b-HgS synthesis (K_1/2 of minutes) and high Hg° evolution, but the rate of the latter decreased rapidly. This is consistent with ecological literature from which Hg° volatilization would be expected to occur from the surface-water interface for only a short time following precipitation. The synthesis of b-HgS appears to require intracellular thiols and active metabolism as interference with either requirement favored Hg° volatilization. Therefore, in the environment cyanobacteria at the air-water interface would primarily act to sediment Hg²⁺ as b-HgS. This suggests that b-HgS, not chelated Hg²⁺ , is the relevant dietary mercurial for algal grazers. In addition, direct exposure to Hg²⁺ may not be appropriate for methylation studies in sediments.