Environmental Engineering Reference
In-Depth Information
deposition to other continents and to the ocean (Dastoor
and Larocque, 2004; Jaffe et al., 2005; Selin et al., 2007;
Dastoor and Davignon, 2009; Jaegle et al., 2009; Jung et al.,
2009; Seigneur et al., 2009; Travnikov and Ilyin, 2009).
Signifi cant efforts, especially in developed countries and in
the Northern Hemisphere, have been made to understand
the atmospheric transport and fate of Hg, which is com-
plicated by the fact that the transformation processes that
convert Hg between its different oxidation states and forms
in the atmosphere is dynamic and can markedly impact
the rate at which Hg is removed from the atmosphere by
wet and dry deposition (Schroeder and Munthe, 1998;
Ariya et al., 2009; Hynes et al., 2009). Mercury can exist
in two oxidation states in the atmosphere (elemental Hg
[Hg
0
] and ionic Hg [Hg
II
]). Whereas Hg
0
is found entirely
in the gas phase, Hg
II
can be present as a variety of forms
in the gas phase and can also be found within or attached
to atmospheric particles. Thus, operationally, three phases
have been defi ned in many studies: gaseous elemental
Hg (Hg
0
), reactive gaseous Hg (RGHg), and particulate Hg
(PHg) (Schroeder and Munthe, 1998; Landis et al., 2002).
Developments in the measurement and analytical tech-
niques for Hg have led to a much improved understand-
ing of the sources and cycling of Hg in the environment,
but the exact impact of anthropogenic activities on the
global Hg cycle is still unclear (Slemr et al., 2003; Laurier
and Mason, 2007; Pirrone et al., 2009), as is the subsequent
conversion and bioaccumulation of MeHg in aquatic food
chains.
Understanding the fate of Hg in the environment, and
the impact of human activity on the biosphere, requires
improved knowledge of Hg fate, transport, and transfor-
mation, which must be derived from a series of coordi-
nated scientifi c endeavors in terms of measurement and
modeling, coupled with interpretation of the results
within a policy framework (Mason et al., 2005; Harris et
al., 2007a; Keeler et al., 2009). An improved understand-
ing of Hg biogeochemical cycling is important if there is
to be a focused and concerted effort to set national and
international priorities and goals for Hg management
and reduction and to develop and implement policies
and strategies. The need to establish baseline concentra-
tions and to document changes to allow assessment of the
effectiveness of global Hg emission reductions, or other
changes in emission distribution, is apparent. Modeling
efforts also require suffi cient data to test and validate the
model parameters (Ryaboshapko et al., 2007a), and long-
term datasets are needed for model testing (Ryaboshapko
et al., 2007b). Finally, by comparing and contrasting
model output and measurements it is possible to under-
stand more clearly the exchange of Hg between reservoirs
and the important reactions. Without this knowledge, the
impact of changes in MeHg in fi sh in response to changes
in atmospheric inputs cannot be properly assessed
(Munthe et al., 2007; Wiener et al., 2003, 2007; Pirrone
and Mason, 2009).
Current atmospheric Hg models have had some success
in predicting the levels and trends in ambient Hg levels in
the atmosphere (Ryaboshapko et al., 2002, 2007a, 2007b;
Lindberg et al., 2007), and similarly, biogeochemical mod-
els of the ecosystem cycling of Hg and MeHg formation
have been relatively successful in the estimation of changes
and trends (Harris et al., 2007a). However, the linking of
atmospheric and biogeochemical models for Hg is still in
its infancy.
There is a critical need for a coordinated Hg monitoring
network designed to track the changes that are occurring
in a variety of ecosystem compartments over time and to
sustain the development of Hg models that can be used to
support policy decisions (Gbondo-Tugbawa and Driscoll,
1998; Hudson et al., 1994; Beals et al., 2002; Roue-Legall
et al., 2005; Trudel and Rasmussen, 2006). A well-planned
network is required to provide a consistent, standardized
set of long-term data on the concentrations and forms of
Hg in all compartments of the biosphere. The overarch-
ing benefi t of such a coordinated monitoring network
would be the universal availability of high-quality mea-
surement data that can support various related activities
(e.g., modeling and management and policy decisions)
(Mason et al., 2005; Harris et al., 2007a). The data from
the set of coordinated monitoring sites would support
the evaluation and validation of models as research and
management tools. Clearly, there is a need to monitor and
assess progress on mandated Hg reductions of controllable
anthropogenic inputs to the atmosphere, as well as the
impact of changes in emissions due to natural variability
and human-induced climate change. A reexamination of
the current status of the measurement and monitoring
of Hg in the global atmosphere is needed to promote the
activities required to support a coordinated and consistent
monitoring program.
In addition, there are many unanswered questions about
the environmental benefi ts of Hg emission reductions in
terms of spatial differences and timescales of response,
and it is not clear what site-specifi c parameters affect these
changes. Some intensive studies have been conducted
(e.g., Evers and Clair, 2005), but the overall applicability
of the results to different ecosystems, or at the continen-
tal scale, is uncertain. Overall, it does not appear that the
present, mostly uncoordinated, data-collection networks
are suffi cient to describe spatial and temporal trends in
environmental Hg contamination (Ebinghaus and Banic,
2009). Clearly, it is crucial for scientists and policy mak-
ers to develop a monitoring framework that can accurately
evaluate the effectiveness of current and impending Hg
regulation.
The notion of a national Hg monitoring network was
fi rst promoted by Dr. William Fitzgerald at an interna-
tional Hg meeting in Whistler, Canada, in 1994 (Fitzgerald,
1995). More recently, development of a monitoring strat-
egy outline for North America began when a group of
32 Hg scientists from academia, industry, government, and
