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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

Lisa Zhang

Lian Liang

Cebam Analytical, Inc


2003: UNEP declared mercuryto be the pollutant of

    • greatest global concern due to its persistence in the environment and its negative effect on human health and the environment.
  • Mercurynow is even more important, because of
    • the UNEPGlobal Legally Binding Treaty on mercury officially launched in this year.

Mercury, an important global pollutant

Components of the global mercury cycle

Due to its biogeochemical cycling & accumulation in Biota


How to put the treaty into practice toward

      • the banning of Hg.
  • Remediation will eventually be conducted at Hg
    • contaminated sites throughout the world.

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


Cebamhas been working on the environmental monitoring

  • of Hg at the Oak Ridge site since1996.
  • The works focused mainly on analysis of Total Hg and Methyl
    • Hg in Waters, Fish, Sediments/Soils, and Air.
  • The data generated were traceable and defensible;
    • Recoveries were within 95 to 105% with RPD <5% for most samples analyzed.


although the monitoring data were at high quality,


were encountered.


While mercury source reduction is a regulatory

  • driver, no direct linkage exists between mercury
  • source reduction and emerging stream protection
  • endpoints such as mercury levels in fish tissue.
  • (Mark J. Peterson, George R. Southworth, and Theresa J. Mathews, Mercury Challenges in the Environment: A
  • Technical Summit, October 22-23, 2009, Nashville, Tennessee).

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.


There is no linkage for THg concentration between waters and fish.

  • At contaminated sites, there is no model
    • relating methyl Hg and THg in water . (
    • Are the data obtained meaningful and useful for
      • characterization of the site?
      • reflecting the remediation activities of the site?

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?



  • Two primary methods:
  • Converting reactive Hg species into chemically inert
    • species such as HgS (themost stable form of Hg).
  • Binding reactive Hg species on various adsorbent
    • materials such as reactive carbon…
  • Therefore, The right way for evaluation:
  • Selecting biogeochemical reactive Hg species/ fractions sensitive to reflect the site and link to methylation for monitoring.
  • Determining how much reactive Hg species/ fractions reduced after remediation.

What Hg species/fractions in waters should be selected?

  • Total Hg (THg)?
  • Elemental Hg (Hg0)?
  • Dimethyl Hg (DMHg)?
  • Monomethyl Hg (MeHg)?
  • Reactive inorganic Hg2+ (RHg)?
  • Depending on the geochemical conditions 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.


Typical chromatography of Hg speciation in water

  • samples from different superfund sites
  • (MeHg, methyl Hg; RHg, biogeochemically reactive Hg2+)
          • A. xxxxxxxx water of Oak Ridge Y-12 site
          • B. surface water of South River, VA
          • C. pore water of Patrick Bayou, TX

RHg: high solubility, mobility, bioavailability, and

    • methylation potential, RHg can directly and immediately
    • reflect the change of Hg levels of contaminated sites.
  • RHg: the predominant reactive Hg species in terms of
    • mass, RHg may be the best species/fractions to use for
    • remediation evaluation at this Hg contaminated sites.
    • However, the use of RHg measurement has not gained widespread acceptance, even after over two decades of practice. The lack of specific analytical methods useful and reliable for identifying and quantifying RHg is most likely the cause of this.

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.


Concentrations of Hg species/fractions measured in the River Idrija in Slovenia. Using the ethylation method, positive and negative bias encountered

  • by the Sn2+ reduction method, was eliminated for determination of
  • RHg in this Hg contaminated river, resulting in meaningful useful data.

Other applications Cebam processed

      • THg
      • MeHg
      • RHg
      • Hg0
    • 300 pore waters from Patrick Bayou Superfund Site, TX
    • 400 surface waters from the St. Louis River, MN
    • 300industrial waste waters from the United States, Europe, and Asia.
  • RHgresults were found to be valuable and meaningful for better
        • characterization and evaluation of remediation of the sites.

Applications of RHg in matrices other than waters

    • Soil,
    • Sediments
    • Crude oils
    • Refinery wastes
  • Key challenge
    • How to selectively extractRHg from various matrices without species shift?

Determination ofRHg in soil/sediment extracts

  • To meet project needs, Different Extraction Procedures
  • Cebam developed/improved procedures
  • TCLP, EPA Method 1311. 1992,
  • Selective Sequential Extraction procedures published by experts in the world

Promising results were obtained.


Selective Sequential Procedures

used in Cebam’s Hg Lab for extraction of RHg


Are there direct linkages between

    • RHg and MeHg?
    • RHg and fish Hg?

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


We recommend to consider RHg for routine monitoring of

  • water, soil and sediment samples
    • at the Oak Ridge site.
  • We need supports to develop useful procedures to meet project needs!


Thank you!

Cebam Analytical, Inc