DOEASP Workshop, Asheville, September 23-26, 2013 Selecting the Right S pecies , Fractions and Methods for Evaluating Remediation Effectiveness at Mercury Contaminated Sites Lisa Zhang Lian Liang Cebam Analytical, Inc . 2003 : UNEP declared mercury to be the pollutant of
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DOEASP Workshop, Asheville, September 23-26, 2013
the Right Species, Fractions and Methods
for Evaluating Remediation Effectiveness
at Mercury Contaminated Sites
Cebam Analytical, Inc
Mercury, an important global pollutant
Components of the global mercury cycle
Due to its biogeochemical cycling & accumulation in Biota
History of Mercury Use and Environmental Contamination
at the Oak Ridge Y12 Plant
Between 1950 and 1963:
~ 11 million kg of Elemental Hg used.
~ 194,100 kg lost to the ground (soil, sediment, storm sewers and old process buildings).
The Area remains a source of mercury in Upper East Fork Poplar Creek
although the monitoring data were at high quality,
THg concentration in fish and water at Y-12, 1988-2008
Fish Hg level is not always sensitive to the changes of water Hg level.
Due to the high bioaccumulation factor,
fish Hg levels can be as high as 1 ppm (depending on size, species and environmental factors)in remote freshwaters (Hg <1.3 ppt) similar to those found in Hg reduced waters (Hg ≈ hundreds ppt) at the Oak Ridge site!
How can we expect fish Hg level to decrease further, and use it to evaluate the remediation of the site?
Comparison of Hg species
RHg, an important species/fractions, was missed in the monitoring for past years!
Comparison of MeHg level
in the Oak Ridge and others sites.
Further, the ratio of MeHg to THg even often shows a reverse pattern, i.e. at higher THg concentrations, the ratio is lower at the Oak Ridge site.
In the past, the classic Sn2+ reduction method has been virtually the only method used for determination of RHg.
Hg2+ + Sn2+ → Hg0↑
Volatile Hg0is measured by purge/trap/CVAFS (EPA method 1631).
Due to insufficient understanding of the reaction conditions, the method was
inadequately used, resulting in negatively biased results,
Unpreserved Clean Water
Effect of purge time on recoveries of SnRHg (RHg results by Sn2+ reduction) in 12 clean river water samples. Results of RHg by ethylation were used as 100% recoveries.
Industrial Wastewater with complex matrices
Effect of purge time on recoveries of SnRHg (RHg results by Sn2+ reduction)
in 12 Hg impacted industrial wastewaters. Results of RHg by ethylation were
used as 100% recoveries
To fill the gap, to ensure reliable results of RHg, Cebam adapted a method by
direct ethylation/GC separation/CVAFS detection
Hg2+ + 2C2H5 → Hg(C2H5)2↑
Volatile Hg(C2H5)2is measured by purge/trap/GC/CVAFS.
Methodology detailed in
Liang L., Horvat M., and Bloom N.S., 1994, Talanta, 41,3,371.
Liang L., Bloom N.S., and Horvat M., 1994, Clin. Chem., 40,4,602
Comparison of ethylation and Sn2+ reduction methods
for determination of RHg
The ethylation method is significantly advanced over the Sn2+ reduction method
RHg by ethylation method
the right species/fractions for
evaluating remediation efficiency
at the Y-12 site
Application of the ethylation method to the determination of RHg in waters
Sampling locations on the river Idrijca
From the Idrijca River, Slovenia. The Idrijca River drains the area of the Idrijca Hg mine, now closed but formerly the world’s second largest Hg mine. This river water contains a significant amount of Hg0 from the mine.
Applications of RHg in matrices other than waters
Determination ofRHg in soil/sediment extracts
Promising results were obtained.
Selective Sequential Procedures
used in Cebam’s Hg Lab for extraction of RHg
In remote lakes, research found that decreases in fish Hg are related to the
atmospheric loading of Hg and SO4 because both substrates are limiting in these
systems (Hrabik and Watras 2002; Watras and Morrison, 2008; Watras 2009). The Metallicus project in Canada made similar findings.
Hg0→ Evaporation→ Oxidation→ RHg formation → Wet deposition→ Methylation → Fish accumulation
Cebam Analytical, Inc