Transcript Lab 8 * Mercury in Forest Soils - Forest Watershed Research Center

LAB 8 – MERCURY IN FOREST SOILS
RELATIONSHIP BETWEEN HG AND ORGANIC MATTER
LAB 8 – MERCURY IN FOREST SOILS
Methylmercury [CH3Hg] = most toxic (immune systems, nerves)
monomethylmercury [CH3Hg]
dimethylmercury [(CH3)2Hg]
Elemental mercury [Hg] = less toxic
- Mercury can be in solid form (silver), but can also be in liquid and
gaseous form.
- Mercury found naturally in small quantities in nature.
- Natural conversions = Some bacteria process sulfate (S04) and
convert Hg to CH3Hg
- Used to mine gold
- Burning coal releases mercury into the atmosphere
HG IN NATURE
Hg cycle from atmosphere to the foliage, sediment, then bacteria that converts it and it goes into the animal cycle.
bioaccumulation
HG AND PROTEINS
HG AND SULPHUR
DMA-80 MERCURY ANALYZER
DMA-80 MERCURY ANALYZER SCHEMATIC
Atomic Absorption
Spectrophotometry
Amalgamation
Thermal Decomposition
Catalytic Conversion
THERMAL DECOMPOSITION
- Sample dried in an oxygen stream in a quartz tube
- The temperature at which a substance will chemically decompose
- The heat breaks down chemical bonds
- Typically 850°C
CATALYTIC CONVERSION
- Combustion products are then carried down through the
catalyst furnace to further decompose.
- Typically 600°C
Traps partially
oxidized residuals
Provides
oxygen to
assist
combustion
Captures poisons (i.e.
sulphur/halogens)
AMALGAMTION
- Mercury comes from the catalyst in vapour form is trapped
in a gold amalgamator
- Hg binds to the gold plate and is then desorbed or released
towards the AAS after other combustion by-products are
flushed away
- Amalgamation furnace is heat and Hg is released. Typically
900°C
ATOMIC ABSORPTION SPECTROPHOTOMETRY
- Atomic absorption used to determine the mercury content.
- Low pressure mercury lamp (254 nm)
- Uses optical radiation (light) to quantify
Absorbance Profile
TIMELINE
LOI AND CARBON
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LOI (loss of ignition) is an indirect measure of organic matter.
C%
Samples are burned in a muffle furnace for 6 hours at 600°C,
then weighed after burning to see the difference in weight.
This shows how much OM (and other elements) have been
burned off. Mineral soil remains behind.
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y = -0.42x + 41
R² = 0.93
5
0
0
- Depending on ignition temperature LOI can cause loss of
salts, structural water, and inorganic carbons which effect
results.
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LOI %
Close relationship between LOI and C%
(MF’s data from central and northwestern NB)
LOI AND CARBON
ORGANIC MATTER AND HG
LOI% vs Hg
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- DOM (dissolved organic matter) has a strong affinity to Hg.
LOI
- Methylmercury is often found in aquatic environments and binds
to metals strongly, affecting solubility, mobility, and toxicity.
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Hg
LAB:
C % vs Hg
- Use LOI (loss of ignition) and C % to see any relationships with
the sites across Fredericton.
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C%
- Colour? Would areas of high colour and therefor high OM show
relationship?
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0
2014 Lab Results
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Hg
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MERCURY IN FREDERICTON?
LAB:
- Compare the Hg measurements across all Fredericton sites
- Analyze (Think & Research) the data for any relationships with
LOI/C% and past quality data.
- Show basic information in appendices (if necessary) and show
graphs/tables of relationship results.
- Discuss the trends found over the years and back it up with any
literature (academic references only).
- Enjoy your last lab!
REFERENCES
Milestone, 2014. Principles of Operation. Retrieved from:
http://www.milestonesci.com/direct-mercury-analyzer/dma80-principles.html