1.7
THE METAALICUS PROJECT: AN EXPERIMENTAL MERCURY MASS BALANCE
T
hroughout its engagement in the modeling of the
The information so gathered should illuminate several
1.7
atmospheric transport and deposition of mercury to
fundamental issues, among them the relationship between
the Great Lakes, the IAQAB has repeatedly acknowl-
the amount of mercury in deposition and quantities of
edged the need for a comprehensive model to track the fate
methylmercury in fish; the speed at which levels in fish
of mercury from deposition into a waterbody to arrival in
would drop in response to a reduction in mercury deposi-
various biota in the water column.  The METAALICUS
tion; and the impact of various environmental factors on
project in the Experimental Lakes Area of Northwestern
the dimension and timing of this response.  These issues
Ontario (Figure 23) is an attempt to track mercury from its
are central to the current consideration of control strategies
initial deposition either on land, wetlands or open waters
for the electrical generation and other mercury emitting
to its presence in fish.
sectors.
A consortium of over 50 United States and Canadian
Entering its third full year, the program has generated
researchers, augmented by scientists from Sweden and
extensive amounts of data, and the publication of out-
supported by governments, academia and the private
comes in the scientific literature is underway and some
sector, is using various application methods to simulate the
papers have already been published.  Integration and
deposition of minute quantities of different stable non-
interpretation of the data is a continuous process and
reactive isotopes of mercury to distinct segments of a
publication of several synthesis papers is anticipated.  In
headwaters lake.  This small (8.3 ha) lake is bordered by a
addition, the nature of the Experimental Lakes Area allows
wetland area of 1.9 ha and an upland drainage area of 42
for long-term monitoring of the fate of the added isotopic
ha, and has a hydraulic retention time of three years.  Small
mercury, hopefully for several years beyond 2003.
confined sub-areas also have been created in the lake for
particular study.
Some preliminary observations are available.  The mercury
added directly to the lake has been detected in the zoop-
The lake is currently subjected to a relatively low mercury
lankton within four weeks of addition and also was
wet deposition flux of 6 µg/m2yr; the experimental
determined both as total mercury and methylmercury in
addition of 25 g (half a teaspoon) of various mercury
the sediments.  It was apparent in fish by late July in the
isotopes over three years will increase this deposition by a
first year.  Up to 14 percent of the methylmercury in fish
factor of four to five, to a rate comparable to that currently
was the isotopic form, with the balance being naturally
observed in some parts of the United States Northeast and
occurring.  Preliminary results indicate that no isotopes
Florida.
from the uplands or wetlands application were found in
the lake.
After preliminary work in 1999-2000, the full scale experi-
ments began in the summer of 2001 and will continue
The extent of the evasion or volatilization of the directly-
through 2003.
applied mercury from the lake to the atmosphere was
estimated at between 20 and 30 percent.
During the experiment, uplands, wetlands and the open
water portion of the basin receive inputs of distinct and
The research consortium maintains a website and meets
different mercury isotopes by means of various techniques
every March to review progress to date and shape the work
(in a lake/water mixture from aircraft, sprayed mixture
over the next season.  Additions of isotopically-labeled
applications on land, dispersion in the lake waters from a
mercury will have ceased by 2004, while the movement
small boat).  After application, the three areas are continu-
through the various compartments of the ecosystem,
ally sampled and analyzed by methodologies able to
including fish, will continue to be tracked.
distinguish among the applied isotopes.  As shown in
Figure 24, this feature allows tracking of the movement of
The IAQAB intends to continue to interact with members of
the mercury throughout the ecosystem to its arrival in fish,
the METAALICUS research team and to use the outcomes of
while sustaining identification of the transfer medium
this study as part of their further consideration of the
(upland, wetland, surface water) of the original applied
mercury issue.
mercury.
39