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Stable
isotope
196
Hg
198
Hg
199
Hg
200
Hg
201
Hg
202
Hg
204
Hg
Relative
atomic mass
195.965 83
197.966 769
198.968 281
199.968 327
200.970 303
201.970 643
203.973 494
Mole
fraction
0.0015
0.1004
0.1694
0.2314
0.1317
0.2974
0.0682
Mercury isotopes in Earth/planetary science
198
Hg, 200Hg, and 202Hg are stable isotopes of mercury that can be used to study environmental
sources and environmental sinks of this element in aquatic and terrestrial ecosystems. For
example, in an ecosystem, different isotopes of mercury can be added to an upland region for
run-off evaluation, to a lake for direct deposition analysis, and to a wetland region for outflow
contribution analysis (Figure 1).
As a result, it is possible to determine the entry points of mercury into an ecosystem and
determine how the inputs of mercury affect the accumulation of this element in local fish
populations. An international consortium of scientists has begun an experiment called
METAALICUS (Mercury Experiment To Assess Atmospheric Loading In Canada and the U.S.).
This experiment includes determination of whether mercury contamination in fish is old or new
mercury. Tracer studies were performed in northwestern Ontario at the Experimental Lakes
Area of the Department of Fisheries and Oceans Canada [543, 544].
Fig. 1: 202Hg was added to small watersheds to study the fate of mercury from atmospheric
deposition in pristine (in its original condition) lakes as part of the METAALICUS study. (Photo
Source: Toxic Substances Hydrology Program, U.S. Geological Survey) [544].
Mercury isotopes used as a source of radioactive isotope(s)
Hg can be used to produce radioactive 203Hg via the 202Hg (n, γ) 203Hg reaction, which is used
in gamma radiation calibration and medical tests [543].
202
Glossary
atomic number (Z) – The number of protons in the nucleus of an atom.
electron – elementary particle of matter with a negative electric charge and a rest mass of about
9.109 × 10–31 kg.
element (chemical element) – a species of atoms; all atoms with the same number of protons in
the atomic nucleus. A pure chemical substance composed of atoms with the same number of
protons in the atomic nucleus [703]. [return]
gamma rays (gamma radiation) – a stream of high-energy electromagnetic radiation given off
by an atomic nucleus undergoing radioactive decay. The energies of gamma rays are higher
than those of X-rays; thus, gamma rays have greater penetrating power. [return]
half-life (radioactive) – the time interval that it takes for the total number of atoms of any
radioactive isotope to decay and leave only one-half of the original number of atoms.
isotope – one of two or more species of atoms of a given element (having the same number of
protons in the nucleus) with different atomic masses (different number of neutrons in the
nucleus). The atom can either be a stable isotope or a radioactive isotope.
neutron – an elementary particle with no net charge and a rest mass of about 1.675 × 10–27 kg,
slightly more than that of the proton. All atoms contain neutrons in their nucleus except for
protium (1H).
proton – an elementary particle having a rest mass of about 1.673 × 10–27 kg, slightly less than
that of a neutron, and a positive electric charge equal and opposite to that of the electron. The
number of protons in the nucleus of an atom is the atomic number.
radioactive decay – the process by which unstable (or radioactive) isotopes lose energy by
emitting alpha particles (helium nuclei), beta particles (positive or negative electrons), gamma
radiation, neutrons or protons to reach a final stable energy state.
radioactive isotope (radioisotope) – an atom for which radioactive decay has been
experimentally measured (also see half-life).
stable isotope – an atom for which no radioactive decay has ever been experimentally measured.
[return]
tracer - substance used for tracking purposes. [return]
X-rays – electromagnetic radiation with a wavelength ranging from 0.01 to 10 nanometers—
shorter than those of UV rays and typically longer than those of gamma rays.
References
543. T. S. I. Inc. Mercury Isotopes. Trace Sciences International Inc. 2014 Feb. 25.
http://www.tracesciences.com/hg.htm
544. T. S. H. Program. Mercury-Contaminated Fish- Is it Old or New Mercury? U.S.
Geological Survey. 2014 Feb. 26.
http://toxics.usgs.gov/highlights/mercury_contaminated_fish.html
703. I. U. o. P. a. A. Chemistry. Compendium of Chemical Terminology, 2nd ed. (the "Gold
Book"). Blackwell Scientific Publications, Oxford (1997).