METALS - Marine Pollution: What Everyone Needs to Know - page 86

1. DEPOSITION OF Hg(II)

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2. SEDIMENTATION

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Hg(II)

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5. BIOMAGNIFICATION of CH 3 Hg

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3. Hg(II) → CH 3 Hg (METHYLATION)

Figure 5.1 Mercury methylation and biomagnification (courtesy Dr. P. Weis)

Although Hg toxicity in highly contaminated areas such as
Minamata Bay is well documented, it can also be a threat to the
health of people and wildlife in environments that are not so
obviously polluted. The risk is determined by the form of mer-
cury and the chemical and biological factors that influence how
it moves and changes form in the environment. Inorganic mer-
cury can get transformed into organic mercury compounds.
Methylmercury (meHg) is a more toxic form, which is pro-
duced from inorganic Hg by the action of bacteria (Figure 5.1).
Bacteria capable of methylating Hg 2+ have been isolated from
sediment, water, soil, and fish tissue. MeHg is the form of Hg
that is most likely to bioaccumulate in fish and other organ-
isms. MeHg, in addition to being far more toxic than inorganic
forms of the metal, also is biomagnified up the food chain, so
tissue concentrations increase as it moves up the food chain.
Mercury contamination and its health implications are impor-
tant internationally. Throughout the world, elevated meHg has
been found in some fish species that are of economic impor-
tance, including shark, swordfish, tilefish, king mackerel, tuna,
and Spanish mackerel, as well as freshwater species such as
bowfin, largemouth bass, and chain pickerel.
The other organometal of concern is tributyltin, but unlike
Hg, tributyltin (TBT) breaks down in the environment,