Mercury Isotopes and Attributing Sources: An
Example from the Great Lakes
David Krabbenhoft
Wisconsin Water Science Center
U.S. Geological Survey
Middleton, Wisconsin
Mercury Concentrations in Sediments Across the Great Lakes
Ares the spatial trends of mercury concentrations in
sediments of the Great Lakes caused by varying source
loading amounts, different sources, or both?
Element : Mercury
29.8
Abundance (%)
30
23.1
20
13.2
10.0
10
200.59
Hg
Mercury
7 stable isotopes
Mass 196 to 204 (4%)
16.8
6.85
0.15
0
196
198 199 200 201 202
Hg isotope
204
Mass independent fractionation of odd mercury isotopes
Where does the isotope effect come from?
- Nuclear volume effect
- Magnetic isotope effect
Adopted from Runsheng Yin
196Hg
198Hg
199Hg
200Hg
201Hg
202Hg
204Hg
High-Resolution Mercury Isotope Measurement used to Define Mercury Source Attribution:
A New Capability of the USGS Mercury Research Lab
Field sampling
Precipita on
Industrial
Precip/watershed
δ202Hg, Δ199Hg, and Δ200Hg
High resolution measurements of Hg
isotopes used for source attribution
Neptune Plus: Dedicated MC
ICPMS for Mercury Research
Mercury Source Attribution: How is it Done?
D199Hg
Source “A”
Source “B”
d202Hg
A Three-Source Example (Tri-Linear Mixing)
D199Hg
Source “B”
Source “C”
d202Hg
Source “A”
Results from Great Lakes Sediments
But, we’ve also discovered a mercury isotope
fingerprint for precipitation - D200Hg. A novel
discovery that can provide independent
confirmation of atmospheric mercury
contributions
D200Hg – An Atmospheric Mercury Source
Attribution Indicator
Source “A”
0%
Source “A”
D200Hg
100%
Fraction of atm. mercury from 3-way source Model
Fraction of atmospheric mercury from single source (D200Hg) Mixing Model
Do Sediments or Precipitation Reflect the Fish?
Seasonal Methylmercury Concentration in
Surface Waters (volume weighted)
April (red)
August (blue)
Great Lakes Sport Fish Mercury Levels
Mean Great Lakes Lake Trout Mercury Concentrations
(2007 – 2009)
Total Mercury (ng/g wet weight)
300
250
200
150
100
50
0
SUPERIOR
HURON
MICHIGAN
ONTARIO
ERIE
But what does that mean for the fish?
Seston-Water MeHg Partitioning Coefficient and Lake Trout HgT
Concentration
8
300
August 2014
7.5
250
Lake Trout
7
200
6.5
150
6
100
5.5
50
5
Lake Trout HgT Conc. (ng/g wet wt.)
Seston-Water MeHg log-Kd (L/kg)
April 2014
0
SUPERIOR
HURON
MICHIGAN
ONTARIO
ERIE
Lake Trout mercury data accessed through the EPA Central Data Exchange database; Lake Erie Lake Trout data created by Tom Holsen at Clarkson University.
Summary:
• The use of mercury stable isotopes as source and pathway
indicators has improved modern mercury science, allowing
us to understand many more details regarding mercury
sources and pathways, BUT you still need the framework
of good basic science as a backbone for interpretation!
• The recent application of this new tool now provides
resource and restoration managers in the Great Lakes
regions (e.g., GLRI program managers for USEPA) new
information for source attribution and decision making.
• The spatial distribution of fish mercury across the Great
Lakes is counter to the loading and aqueous THg and
MeHg levels, but aligns well with lower trophic levels of Hg
and MeHg … what does this say about relative
bioavailability of atmospheric Hg versus tributary and/or
point-source releases??
Next Steps:
It’s time to find out if we have possibly been
comparing limes and watermelons!
Hg Hg
Hg
MeHg
Hg
Hg
Hg
Hg Hg Hg Hg
Hg
Hg Hg Hg
Hg
Sediments
MeHg
Fish