The Chemical Cycle and Bioaccumulation of Mercury paper

The Chemical Cycle and Bioaccumulation of Mercury paper by: Francois Morel, Anne Kraepiel, and Marc Amyot presented by: Roxanne Myshkowec class: CE 468 3/2/00

Introduction b The purpose of the paper was to answer the question: “How do concentrations of parts per trillion of mercury in water yield concentrations of parts per million in fish? ” b The answer is reached by examining the chemical and biological mechanisms that control the cycle.

Topics of Discussion b Background information on Mercury b Describe the global mercury cycle b Discuss chemical and biological influences on the cycle b Discuss bioaccumulation of mercury in fish b Conclusions

Background Information b common species: • elemental mercury: (Hgo), ionic mercury: (Hg +2) complexes, and organic mercury: (CH 3 Hg+) b sources: • burning of fossil fuels, industrial, pesticides, volcanoes, amalgams b health risks: • depends on species: inorganic- kidney, organic- CNS, possible carcinogen b MCL: 2 micrograms/liter

Global Mercury Cycle b b Long range transport as result of residence time coupled precipitation/volatilization cycle 2/3 mercury in atmosphere result of anthropogenic sources inputs tripled in last 150 yrs

Depth profiles

Chemical and Biological Influences b OXIC WATERS: 5 -100 p. M total Hg b reduction of Hg +2 : • photoreduction vs. microbial reduction (dependent upon concentration) b oxidation of Hg o • thought to be negligible b demethylation: CH 3 Hg+ + H+ = CH 4 + Hg+2 • requires enzymatic or photochemical catalyst b methylation • unknown microbial process

Chemical and Biological Influences Cont. ANOXIC WATERS: Hg+2 high affinity for sulfide dominates b reduction of Hg +2 : • microbial vs. humic substances pathways b methylation: • photochemical vs. microbial catalyzed pathways

Aquatic Cycle

Bioaccumulation b microbial uptake: • transported into cell by mer T transport protein • transported by diffusion through lipid membrane b speciation and Kow effect uptake • uncharged species have higher uptake yields b reactivity in cell effects accumulation. • Organic mercury better retained since more reactive than Hg+2

Bioaccumulation

Conclusions b answer to question- bioaccumulation b bioaccumulation and thus toxicity dependent on speciation b by examining mercury cycle can begin to understand the chemical and biological influences that control speciation b in future better examine water-sediment interface reaction and unknown microbial interactions