Toxic elements!!

Going to dental school I get to learn lots of neat things. Controversial things. Things that will get you in trouble with the Feds. Stuff like why mercury is used in silver fillings! Why bleach is used in root canal procedures! And *gasp* why flouride is put into drinking water!!!!!!!! It might not get you in trouble with the Feds, but it might get some vegans upset.

No one says these substances aren't dangerous, just useful for their task without enough danger to keep from using them. In biochemistry we discussed the various aspects of Mercury yesterday and since I should be studying for a test for Monday morning, I'll review it here and call it studying.

Basics review: Every element known to man has a neutral state where it has equal numbers of protons as electrons. Hydrogen has 1:1, Lithium has 3:3, Oxygen has 8:8, carbon has 6:6, etc. But there are various types of electron orbits and the proportion to electrons in their orbits to the protons causes some funny things. Many elements do not like to be neutral and you would be extremely hard-pressed to find them neutral in nature. Sodium (and related metals) metal HATES being a neutral guy and will react explosively with anything to toss off an electron (usually it's onto water, since that's such an abundant substance that's so lax with it's electrons) and gain a positive charge. Chlorine is the opposite, it HATES being neutral but would rather steal someone else's electron, to get a negative charge (since it's normally a gas, this makes it dangerous to living things that can inhale it so easily where it wreaks havoc on all the electron-transferring reactions that make life possible). While these guys like being non-neutral, they still have to submit to electromagnetism and will stick together positives with negatives, thus, table salt: Sodium chloride (the -ide notes it's non-elemental state, just a formality). An atom with a charge (non-neutral) is called an ion, and larger atoms (especially metals) tend to have multiple stable ion forms.

Mercury is the same way. You can find it in nature as neutral liquid shiny metal form (not common), usually in a rock with other minerals of various charges or dissolved in water with a +1 or +2 charge, or it can be solidly attached to organic molecules like methane and ethane (methyl mercury and ethyl mercury). In toxicity, elemental mercury is the least toxic (like in thermometers and silver fillings), the organic being the most toxic (as found in tuna). 

The World Health Organization and OSHA set safety standards on mercury in general and don't differentiate between the types (since none are safe in large amounts). WHO says the max allowable should be below 42 micrograms per day and that the normal is about 25-30. In our Operative Dentistry class they told us that OSHA limits it to 16.7 micrograms/day and that we get between 10-20 micrograms per day. The difference, I think, is due to the differences between our country and other countries without standardized safety protocols etc. 

Both professors agreed that a dozen or so fillings provides the person with about 2-3 micrograms per day of elemental mercury vapor. Not negligible, but on the smallish side. A few small fillings will give you about .3-.7 micrograms per day. Other mercury ingestion is through fish/seafood, water and other sources.

A common way to measure mercury intake is by measuring food and water and such, but not as reliable. Another way is to measure what comes out in urine and feces. Elemental mercury is absorbed by the lungs (not so easily through skin, but does happen), organic mercury absorbed in your intestines. Some elemental mercury can be converted by your body (as a by product) into Mercury +1 or +2, especially in your nerves. 

To put in perspective how bad mercury is for a person, here's the table given in Biochemistry:

500-1000 micrograms/day=Kidney failure, swollen gums, nervous system problems

100-500 = Irritability, depression, memory loss, early kidney problems

25-100 = subtle changes in tests, but no obvious symptoms, some decreased brain-wave function and verbal skills

0-25 = no known health effects.

(purportedly, dental personnel excrete 12-15 micrograms/day).

The most dangerous exposure of people to mercury is to those in industrial careers/locations when huge amounts are disposed of (Illegally) into water sources or other places. This is rare nowadays (probably more common in the late 1800's and early 1900's, or not long ago this happened once in Japan, they got caught because of abnormal amounts of birth defects in children in the vicinity.

Oddly, there exists bacteria that can convert organic mercury into elemental mercury. Scientists have cut and pasted the genes for that enzyme into cottonwood plants for testing and then grown them in exposure to organic mercury and the transgenic test plants are much healthier. Weird. There's bacteria for everything somewhere in the world except bacteria that can live off of synthetic oil-products like plastics, the world might fall apart should one get evolve and get out. As far as we know nature/life hasn't figured out how to pull organic energy from plastic.

So, there you have it. More than you wanted to know about mercury and it's dangers. If you've wondered how dental fillings go from moldable to hard, the silver, zinc, and copper are super powdery and when mixed with the liquid mercury take about 10 minutes to crystallize into the amalgam filling in your tooth (and is even changeable up to about a day). It goes from buttery-creamy consistency to hard metal during the working time. 

If a dentist ever tells you that amalgam/silver fillings are dangerous for you, remind him he's in danger of losing his license, because that's just not true. If they say that you should have your silver fillings removed for health reasons, that's especially bad and he's just digging for business, especially since you'll be exposed to more mercury while he/she drills them out than you would be just leaving them there.

On the reverse, the substances used in composites/resin/white fillings used nowadays aren't entirely safe either, so hedge your bets. Amalgam is the superior filling material, but definitely not as nice to look at. 

One last tidbit: Mad Hatter's disease (like the mad hatter in Alice in Wonderland) was caused because hatter's would rub liquid mercury into the felt while making hats. Also, rub-a-dub-dub three men in a tub supposedly refers to the practice of having guys with syphilis sit in tubs of mercury to treat the STD (at least that what the teachers say...). Apparently it worked decently.