MERCURY ISOTOPE RATIOS AS CONTAMINATION MARKERS: PROCEDURE DEVELOPMENT AND APPLICATIONS

Mercury is one of the most harmful elements present in the Earth, and has
both natural and anthropological sources. Moreover, Hg can undergo to
many different transformation pathways during its biogeochemical, or
industrial, cycles which in general involve redox reaction, both abiotic and
biotic, and phase changes (1). Despite the toxicity of this pollutant, there is
still a lack in the knowledge about the biogeochemistry of mercury in the
ecosystem and, therefore, it is of utmost relevance to develop new scientific
approaches to understand its transformation mechanisms and to identify its
contamination sources. In this context, the determination of mercury stable
isotopes ratios and, in particular, the identification of fractionation processes
seems to be an extremely interesting and challenging application to verify
the “provenance” of the element. Mercury, in fact, undergoes to both mass
dependant, MDF, and mass independent fractionation, MIF, processes. In
particular the MIF, involving only the odd isotopes (199Hg and 201Hg),
appears to be a characteristic fingerprint of the process and the pathways
involved in the Hg transformations (2). Thus, the study of both fractionation
phenomena can be a powerful tool to identify its natural or anthropogenic
source. This approach can be useful in case of polluted areas where many
are the contamination sources in order to plan an environmental
requalification. An intriguing case study is represented from the National
Interest Site of the lagoon of Marano-Grado (Trieste, Italy), which is object
of the present study. For these purposes, the evaluation of the isotopic
composition in samples coming from this area has been performed by means
of an HR-MC-ICP/MS system for the simultaneous determination of all the
isotopes of interest (3). Due to the difficulties of the mercury ICP
determination and the high number of the acquisition parameters the
optimization and the validation of the analytical procedure was required, in
order to obtain highly accurate and precise data. After this first step the
method has been applied for the determination of the Hg isotopic
fingerprints in environmental samples (e.g. sediments) coming from the
Marano-Grado area.
(1) W. Fitzgerald, C. Lamborg, Treatise on Geochemistry 9, Elsevier, 2004.
(2) B. Bergquist, J. Blum, Elements, (2010), 353-357.
(3) D. Foucher, H. Hintelmann, Anal. Bioanal. Chem., (2006), 1470-1478.