Abstract

1. Comparison of Sn2+ reduction and ethylation based methodsfor determination of reactive inorganic mercury in waters • Lian Liang1*, John Alvarez2, Lyman Young2, Milena Horvat3, Elizabeth A. Bennett1, Patrick Pang1 • 1.Cebam Analytical, Inc., USA 2. Chevron Energy Technology Company, USA3. Department of Environmental Sciences, J. Stefan Institute, Slovenia Abstract Two methods based on, Sn2+ reduction and ethylation, for determination of RHg were compared in chemistry, analytical methodology and field sample analysis. Factors that may affect results by Sn2+ reduction method were investigated. It was found that results were independent of chemical factors, pH and Sn2+ concentration, but strongly dependent on physical factors, purge time and purge gas flow rate. Results by Sn2+ reduction were found to be irreproducible and slightly biased low in clean waters, but dramatically biased low in Hg-impacted waste waters. Irreproducible and biased low results were similarly found in determination of elemental Hg (Hg0) by purge without Sn2+ reduction involved. RHg results by Sn2+ reduction can be equivalent to those by ethylation only when reduced Hg0 is purged for enough time. The necessary purge time can be as long as several days, or even longer depending on amounts of reduced Hg0 and matrix complexity. Due to its significant advantages in methodology, and great scientific implication, the ethylation-based method is recommended for determination of RHg. Application of the ethylation method to determine RHg in impacted river waters To demonstrate the efficacy and usefulness, as well as advantages of the new ethylation approach, water samples from the river Idrija were collected in the summer of 2012 for the investigation. The river Idrija drains an area of a former mercury mine in Slovenia. Five locations were selected along the Idrijca (Figure 9) representative of different levels of Hg impact and transformations on the basis of results reported in previous studies. The first location, above Belca inflow, is a pristine site with very low mercury, while all the downstream sampling sites are affected by the mercury mine to some extent The second site, in the town of Idrija, is the location where the mine drainage entered the river. It also contains natural outcrops of elemental mercury on the riverbanks and is therefore heavily impacted with mercury of both anthropogenic and natural origin. Results are illustrated on Figure 10, 11, 12 13. Matrix interferenceon ethylation reaction using ethylation method Matrix interference was found to be easily eliminated by simply diluting the samples because the ratio of RHg to MeHg generally ranges from 10 to 10n depending on the site, and the more impacted the site is, the greater the value of n. This allows performance of the determination in diluted samples without matrix interference. Stability of RHg in unpreserved water samples (figure 8) Introduction Although RHg was well recognized to be an important species due to its methylation potential in Hg biogeochemistry cycling, 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. To fill the gap, a technique based on an ethylation reaction was adapted for speciation and quantification of RHg., Experimental Hg species and related analytical procedures involved in this work are summarized in Table 1 below. Except those specifically described, reagents, standards, and parameters are referred to EPA methods. Results and Discussion Effects of experimental conditions on RHg results by Sn2+ reduction method The effects of chemical/physical conditions on results were shown in figures 1, 2, 3, 4. Determination of RHg in soil/sediment and other samples The use of ethylation-based method for RHg in sediment/soil and crude oils has been analyzed after extraction of RHg from various matrices using different extractants and procedures, and the method was found to be promising. Conclusion Table 2, Comparison of ethylation and Sn2+ reduction methods for determination of RHg Recoveries and purge behaviors of RHg are shown in figure 5, 6, and 7. Acknowledgements:The work is partially supported by Chevron Energy Technology Company under Contract CW831200, and also partially funded by the Slovenian Research Agency (ARRS) through a programme P1-0143 and project J1-4288. V. Fajon and Jožekotnik are acknowledged for sampling of the water samples from the river Idrijca.