1.2
AN ECOSYSTEM APPROACH TO THE HEALTH EFFECTS OF MERCURY IN THE GREAT LAKES BASIN
I
n 1998, Health Canada’s Great Lakes Health Effects
Program compiled data and statistics on mortality,
The total mass of mercury in the atmosphere has
morbidity and congenital abnormalities that might be
linked to pollution in Areas of Concern.  Cerebral palsy had
been estimated to be between 5000-6000 metric
been included because of the association with the popula-
tonnes  (Fitzgerald  and  Watras,  1989)  with
tion exposures to methylmercury both at Minamata, Japan
in the 1950s and in the Iraq population in the 1960s and
approximately half due to anthropogenic sources
1970s.  These Health Canada reports indicated that there
(Lindqvist et al.,1991).
were statistically significant increases in hospitalization
rates for cerebral palsy in certain Areas of Concern com-
pared with the rest of the province of Ontario.  Several of
these Areas of Concern also had a history of large industrial
Mercury in its elemental state has low reactivity and a long
uses of mercury, particularly for manufacturing chlorine
atmospheric residence time, thus allowing it to be mixed in
and sodium hydroxide.
the atmosphere on a global scale.  Reactive gaseous
mercury is very soluble in water and thus is effectively
Mercury (Hg) is a heavy metal and naturally occurring
scavenged by wet deposition (Fogg and Fitzgerald, 1979;
element that has been mobilized by anthropogenic
Mason et al., 1994).  Particulate forms are removed by dry
activities and contaminated the environment. Many
deposition (Keeler et al.,1995).  Once removed from the
activities lead to this global pollution, including the
atmosphere, much of the deposited mercury ends up in
burning of municipal trash, burning of high sulfur coal
aquatic systems due to direct deposition and transfer from
containing cinnabar (HgS) in coal-fired power plants,
the terrestrial ecosystem to aquatic ones (Mierle and
smelting, chloralkali plants, and gold extraction, as well as
Ingram, 1991).  Mercury effects on fish, birds and mammals
from historical uses of fungicides containing mercury, latex
that eat contaminated fish are of significant concern
paints, and in the pulp and paper industry.  Atmospheric
(Wiener et al., 2003).  Our public health and wildlife
concentrations peaked in the 1960s–1970s, and have been
concerns about mercury stem from exposure to the
declining since then (Engstrom and Swain, 1997).  It has
methylated form, MMHg.  In anaerobic environments, such
been estimated that human activities contribute 70-80
as lake sediments, mercury is transformed to MMHg by
percent of the total annual mercury to the atmosphere
microbial action, most notably by sulfur reducing bacteria.
(Fitzgerald 1995) and that greater than 95 percent of the
The MMHg diffuses into the water column where it can be
atmospheric mercury in the vapor phase exists as elemental
taken up by fish, accumulating in their muscle tissue by
mercury. There is a very dynamic redox cycle and exchange
binding to thiol groups.  MMHg is the most toxic form of
between the oceans and atmosphere (Mason and Sullivan,
mercury and causes neurological, liver and kidney damage,
1997). The remaining balance of the mercury exists as
as well as neurodevelopmental effects in children
oxidized reactive gaseous mercury, particulate complexes
(Davidson et al., 2000; Grandjean et al., 1997; NRC 2000).
of divalent mercury, and as monomethylmercury (MMHg)
Reproductive effects also have been documented in fish
(Stratton and Lindberg, 1995a;1995b).  The total mass of
and fish-eating wildlife (Hammerschmidt et al., 2002;
mercury in the atmosphere has been estimated to be
Scheuhammer 1991).  In the United States, 45 states advise
between 5000-6000 metric tonnes (Fitzgerald and Watras,
the public against unlimited consumption of freshwater
1989) with approximately half due to anthropogenic
fish due to their MMHg levels.  In addition, the U.S. FDA
sources (Lindqvist et al.,1991).
has issued a mercury-based national fish consumption
advisory for five species of commercial oceanic fish.  The
U.S. EPA considers an acceptable dose of mercury to be 0.1
µg/kg body weight/day, and this was recently supported by
an independent study of the National Academy of Sciences
(NRC 2000).
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