The Effects of Solar Radiation on Dissolved Gaseous
Mercury Variations in the Raquette River
Lauren Gorgol1, Dustin Nuhfer2, Hyun-Deok Choi3, Dr. Thomas
Holsen4
The contamination of water bodies with high mercury levels is a growing concern in many parts of the
United States. Large amounts of mercury are emitted into the atmosphere through fossil fuel burning and
are deposited back to land and surface waters in many different pathways and locations as part of the
mercury cycle. Once mercury reaches a water body it can be transformed to methylmercury by
microorganisms. Methylmercury is taken up by biota and stored in the fats of small fish feeding on the
biota. Bioaccumulation up the food chain results in hazardous methylmercury levels in predatory fish.
This affects fish populations and raises public health concerns for human consumption of these fish
(Amyot et al, 2004).
An important component in the mercury cycle is dissolved gaseous mercury (DGM). DGM consists of
elemental mercury Hg0, which is non-water soluble and non-reactive and thus easily volatilizes from a
water body to the atmosphere. Research has shown that the rate of DGM volatilization is directly related
to solar radiation, in which DGM production peaks at mid-day and reaches a low before sunrise the
following day. This diurnal cycle is due to the photo-reduction of water soluble reactive mercury (Hg2+ )
to non-water soluble Hg0. Hg2+ enters a water body through precipitation, and is then converted to
volatile Hg0 by this process. Understanding DGM production is an important part of the mercury cycle as
it is the only way that mercury can volatilize from a body of water (O’Driscoll, 2003).
The aim of this research project was to develop techniques to measure DGM and then use these
techniques to study the relationship between solar radiation and DGM production in the Raquette River.
Solar radiation was measured every five minutes with a Davis Vantage Pro 2 weather station outside of
the Rowley Laboratory Building at Clarkson University. DGM was measured using a specially designed
gas stripping reactor connected to a Tekran 2537A Mercury Vapour Analyzer. The experimental set-up
and reactor is shown in Figures 1 and 2. Samples were taken every 2 hours at the riverside with a 2L glass
bottle and then taken back to the laboratory for analysis. The time of sampling ranged from
approximately 6am until 12am the following day.
Zero Air
Generator
mercury-free
air
Tekran 2375A Analyzer
Air with captured
mercury
Reactor
Figure 1: Experimental Set-up
Figure 2: Reactor
1
Class of 2008, Environmental Engineering at University at Buffalo, Environmental REU Program, Dr. Holsen. Oral
Presentation
2 Class of 2011, Clarkson University, Honors Program, Dr. Holsen. Oral Presentation
3 Ph.D candidate, Department of Civil and Environmental Engineering, Clarkson University.
4
161 Clarkson University.
Professor, Department of Civil and Environmental Engineering,
161
Figure 3 shows the relationship between solar radiation and DGM concentration in the Raquette River for
the combined days of July 10, 12, and 18. Solar radiation values were time shifted by 90 minutes in
advance of sampling and averaged over one hour to obtain the best correlation. Time shifting analysis has
been performed in prior research of DGM and solar radiation correlation with greatly improved results
(O’Driscoll, 2003). The graph shows a strong positive relationship when fitting a linear trendline to the
data with an R squared value of 0.895. The high R squared value obtained suggests that DGM
concentration can be approximated by solar radiation data with the equation y = 0.0365x + 22.7.
y = 0.0365x + 22.7
R2 = 0.895
70
DGM concentration (pg/L)
60
50
40
30
20
10
0
0
200
400
600
800
1000
1200
Solar Radiation (W/m-2)
Figure 3: DGM concentration as a Function of Solar Radiation
Further research to contribute to understanding DGM variations due to solar radiation in the Adirondack
region would include measuring DGM levels in the nearby Grasse and St. Lawrence Rivers. Another
possibility area of research is to measure DGM variations throughout the year to analyze DGM under a
wider range of solar radiation.
162
References
Amyot, M., Southworth, G., Lindberg, S.E., Hintelmann, H., Lalonde, J.D., Ogrinc, N., Poulain,
A.J., Sandilands, K.A. Formation and evasion of dissolved gaseous mercury in large
enclosures amended with 200HgCl2. Atmospheric Environment. 2004, 38, 4279-4289.
O’Driscoll, N.J., Lean, D.R.S., Loseto, L., Carignan, R., Siciliano, S.D., The effect of dissolved
organic carbon on the photoproduction of dissolved gaseous mercury in lakes and the
potential impacts of forestry. Environmental Science and Technology. 2004, 38, 26642672.
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