LAB 8 MERCURY IN FOREST SOILS RELATIONSHIP BETWEEN HG AND
ORGANIC MATTER
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LAB 8 MERCURY IN FOREST SOILS Methylmercury [CH 3 Hg] = most
toxic (immune systems, nerves) monomethylmercury [CH 3 Hg]
dimethylmercury [(CH 3 ) 2 Hg] 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 CH 3 Hg - Used to mine gold - Burning coal
releases mercury into the atmosphere
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HG IN NATURE Hg cycle from atmosphere to the foliage, sediment,
then bacteria that converts it and it goes into the animal cycle.
bioaccumulation
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
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CATALYTIC CONVERSION -Combustion products are then carried down
through the catalyst furnace to further decompose. -Typically 600 C
Captures poisons (i.e. sulphur/halogens) Provides oxygen to assist
combustion Traps partially oxidized residuals
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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
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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
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TIMELINE
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LOI AND CARBON LOI (loss of ignition) is an indirect measure of
organic matter. 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. - Depending on ignition
temperature LOI can cause loss of salts, structural water, and
inorganic carbons which effect results. Close relationship between
LOI and C% (MFs data from central and northwestern NB)
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LOI AND CARBON
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ORGANIC MATTER AND HG - DOM (dissolved organic matter) has a
strong affinity to Hg. - Methylmercury is often found in aquatic
environments and binds to metals strongly, affecting solubility,
mobility, and toxicity. LAB: - Use LOI (loss of ignition) and C %
to see any relationships with the sites across Fredericton. -
Colour? Would areas of high colour and therefor high OM show
relationship? 2014 Lab Results
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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!
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REFERENCES Milestone, 2014. Principles of Operation. Retrieved
from:
http://www.milestonesci.com/direct-mercury-analyzer/dma80-principles.html