School Science Lessons
Mercury
2012-05-12 SPwp
Please send comments to: J.Elfick@uq.edu.au
Table of contents
3.0.0 Mercury, Hg,
Table of the elements
Mercury and dental amalgam: 3.0.0
Mercury cell has mercury cathode, mercury barometer, mercury solvent of
metals to form amalgams,
mercury vapour lamps
Mercury in barometers and thermometers: 3.3.4
Mercury mineral: 35.20.26 (Geology)
Mercury metal, redistilled, quicksilver, (alchemist: azoth): 7.0.6
Mercury properties: 7.2.2.27
Mercury residues: 3.4
Mercury toxicity: 3.6.10
Pressure definitions: 12.1.01
Reactions of mercury compounds: 12.8.4
Tests for mercury- no test in this document
Toxicity, poisons and FIRST AID: 3.10.0
(See Mercury)
3.0.0 Mercury and dental amalgam
Statement approved by the 107th session of the National Health and Medical
Research Council, Sydney,
Australia.
"An amalgam is a metal alloy where one component is mercury. Dental amalgam
is prepared by mixing
silver-tin powder with liquid mercury. The resulting
mix then hardens to form a stable solid as mercury
forms compounds with
the silver and tin.
Dental amalgam is an excellent material for repairing decayed teeth, and
for many applications it is still
preferable to the alternatives. Amalgam
is stronger, and therefore lasts longer than the composite resins
(plastics)
or synthetic cements. Amalgam is chemically much less damaging to the local
tissues than these
materials, and it keeps bacteria out extremely well.
As some forms of mercury are toxic, the safety of dental amalgam for dental
patients, and for dental care
workers, has been thoroughly examined.
The vapour of pure mercury does pose a health hazard if it is inhaled either
in very high concentrations for
a short time or in moderate concentration
for months or years. Mercury vapour crosses the lungs into the
blood quite
readily, and then moves from the blood into other tissues. This is a possible
risk to dental
health workers if mercury hygiene is not practised and their
workplace becomes contaminated; but it is
not a risk to patients receiving
amalgam fillings because of them, the exposure to vapour is extremely low
and occasional inorganic mercury compounds, such as those formed when dental
amalgam is mixed, are
poorly absorbed is readily excreted by the kidneys.
Mercury compounds are present in many foods in
low concentrations and cause
no harm.
The health and well being of dental patients who have received amalgam fillings
has been studied
thoroughly, and the following findings were arrived at:
(1) There is no difference in the incidence of any disease or in the length
of life between people who have
amalgam fillings and those who do not.
(2) People who have amalgam fillings and then have them removed do not experience
an improvement in
health.
(3) People who have no teeth, and therefore no amalgam fillings, are not
healthier than people with
amalgam filled teeth.
(4) Rarely, allergy to amalgam occurs as a local rash on the cheek or tongue
next to a filling. For patients
with such allergy, material other than amalgam
should be used.
Dentists and dental researchers are interested In finding ways to repair
teeth without using dental amalgam,
because of the industrial risks which
amalgam poses to dental care personnel. Patients sometimes request
fillings
made with materials other than amalgam, because of the concerns about safety
and appearance.
Some alternative materials can be used, but they are often
less satisfactory than amalgam from the point of
the patient's long term
health and well being.
Dental amalgam is still the material of choice for the repair for most medium
sized areas of tooth decay in
premolar and molar teeth.
The objective of the National Health and Medical Research Council is to
advise the Australian
community on the achievement and maintenance of the
highest practicable standards of the individual and
public health and to
foster research in the interest of improving those standards."
[Editorial comment: The research is not very clear and confusing. Properly
and accurately mixed
amalgams are probably sufficiently stable to not cause
any problems over a lifetime. Inaccurately mixed
amalgams may leak (leach)
enough mercury to cause some minor effects after a long time in a small
number
of genetically pre-disposed individuals. Another issue for the dental professions
was what else to
use? It has only been in the past few years that useful
alternatives have been available.
About half the current dentists use the alternatives. Previously students
studied the interesting chemistry of
mercury salts. To my knowledge, there
has not been one health problem related to mercury in these
thousands of
students.]
3.3.4 Mercury in barometers and thermometers
1. Do not use mercury in school experiments.
2. Senior secondary classes may use barometers and thermometers containing
mercury but primary and
junior secondary classes should use alcohol thermometers
and may observe a mercury barometer
attached to the wall if supplied by the
education authority.
3. Thermometers supplied to schools usually contain alcohol and not mercury.
Avoid leaving thermometers
in containers where they are easily knocked over
by students. To monitor the temperature continuously,
clamp the thermometer
in position. If recording the temperature at regular intervals, return the
thermometer
to its container between measurements. Do not leave thermometers
on the desk where they may be
moved by the elbows or the back of the hand.
Do not place normal thermometers in the mouths of
students. Do not use thermometers
to stir liquids because the liquid in the thermometer may separate,
making
it unusable. However, you can put the thermometer in a refrigerator freezer
until the liquid
recombines. Do not try to recombine the liquid by heating
the thermometer because it may explode.
4. Do not make a barometer or a thermometer using mercury. Mercury vapour
is Toxic and may damage
the nervous system. Mercury enters the body readily
by inhalation by ingestion or through the skin. If
mercury is spilt from
a broken thermometer, immediately pick up all the mercury with pieces of
stiff
cardboard, e.g. a bent playing card, or with a damp cloth or a water
suction pump. Do not use a vacuum
cleaner or a broom. Do not put spilt mercury
down the drain. Sprinkle sulfur powder or zinc powder over
the area of the
spillage and collect it with a moist absorbent paper. Shine a light on the
spillage to see the
mercury globules. Report any mercury spill to the school
authorities. Give any spilt mercury or mercury
stored in the school laboratory
to a government laboratory.