15: Heavy metals Flashcards
Two heavy metals of concern
Mercury (Hg), lead (Pb)
Problems associated with heavy metals
- associated with particulate matter, easily transported in the atmosphere (dissolve in water and volatile)
- Toxic, even in low concentrations
- Can bioaccumulate
Characteristic of Mercury. Mined in what form?
Extremely volatile liquid
Often mined in the form of cinnabar (deep red crystal used as pigment and in jewelry; Mercury sulfide HgS)
When was Mercury first mined? What did the early chinese believe?
First mined in Spain over 2000 years ago; miners got sick and died
Early Chinese thought cinnabar would prolong life
Where does the term “Mad as a hatter” come from?
Twitching and dementia, once common among hat makers who dipped felt in mercuric nitrate to soften it
Three common forms of mercury
- Elemental mercury (Hg^0): can be mixed with other metals to form alloys
- Inorganic mercury (Hg^2+): ionized mercury, ions w 2+ or 1+ charge
- Organomercury (mostly MeHg+): highly toxic. Methylmercury is a common form.
Characteristics of organomercury
- more toxic than elemental mercury (so are inorganic merc)
- readily absorbed through skin and is bioavailable to organisms (unlike elemental and inorganic)
Slide 10,11,12
The mercury cycle
Methylation of mercury
Explain how mercury is toxic
- It is a neurotoxin and a teratogen
- increases oxidation and oxidative damage in the body, esp the brain
- exposure to mercury in pregnancy can cause severe birth defects
What makes methylmercury so toxic/the most common cause of mercury poison? Why does this happen?
It is readily absorbed by the digestive tract of humans (as opposed to other forms)
From there is can be transported easily across the blood-brain barrier and across the placenta
This is bc it binds to the aa L-cysteine and the body mistakes this complex for a diff essential aa, L-methionine
What happened with mercury in Minamata bay?
1930s/40s a chemical company wanted to help the economy in communities like Minamata
They built their factory to make acetaldehyde using mercury based catalyzer on the bay
They dumped methylmercury into the bay, which ended up in zooplankton, phytoplankton and fish
Realized it caused disease in 1950
Slide 17
What is Minamata disease? Symptoms?
Disease caused by methylmercury poison. Mostly in children (transported in the placenta)
Symptoms are ataxia, numbness in extremities, paralysis, coma, affects speech, poor coordination
First identified in feral cats with poor coordination
How did the people with Minamata disease accumulate so much mercury?
It is a fishing village; relied on fish for sustenance
Methylmercury also bioaccumulates and biomagnifies
Example of Minamata disease in Canada?
Grassy Narrows reserve
Paper plant dumped tons of Hg into the river decades ago
Two ways to decrease the amount of mercury produced
- Stop using coal/fossil fuels as energy
- Stop using (and learn to dispose properly of) products with mercury (small batteries, lightbulbs, thermometers)
