Lec 19 Flashcards
(52 cards)
Heavy metals of concern
Mercury (Hg)
Lead (Pb)
Problems with heavy metals
Associated with particulate matter, easily transported in the atmosphere
Toxic, even in low concentrations
Can bioaccumulate
Mercury
Extremely volatile liquid
Often mined in the form of cinnabar
Common forms of Mercury
Elemental mercury (Hg 0) (can be mixed with other metals)
Inorganic mercury (Mostly Hg 2+)
Organomercury (Mostly MeHg+) (Highly toxic)
Organomercury
Compounds and ions of mercury, especially organomercury compounds are more toxic than elemental mercury
It is readily absorbed through skin and is bioavailable to organisms (as opposed to elemental and inorganic mercury)
The mercury cycle
Elemental mercury oxidates to become inorganic and methylates and bioaccumulates to become Organomercury which spreads
Methylation of Mercury
Ionized mercury in seawater and sediments cannot enter bacterial cells
With little or no oxygen available, some bacteria use SO4 for respiration, expelling sulfide as a waste product
Sulfide combined ionized mercury in seawater to form mercuric sulfide, which can diffuse into bacterial cells
Inside bacterial cells, a methyl group replaces the sulfide to produce monomethyl mercury, which diffuses into seawater and is taken up by phytoplankton
Methylation of mercury equation
SO4–>S
S+ Hg–> HgS
HgS + ? –> CH3Hg
Toxicity of mercury
Mercury is neurotoxin and teratogen
Increases oxidation and oxidative damage in the body, especially the brain
Exposure to mercury in pregnancy can cause severe birth defects
Most instances of mercury poisoning due to contact with
Organomercury, and partially methylmercury
Why is methylmercury so toxic
Relatively absorbed by the digestive tract of humans
From there it can be easily transported across the blood-brain barrier, and across the placenta
Amino acid L-cysteine and mercury
Mercury binds to L-cysteine and the body mistakes this complex for another amino acid and allows it to be transported across the blood-brain barrier
Minamata Bay
An area where a large amount of Methylmercury poisoning occurred
Caused by Chisso Corporation methylmercury wastewater
How did the mercury accumulate so much in people of Minamata Bay
The people had a large fish diet and bioaccumulated mercury from them
Asubpeeschoseewagong First Nation (Grassy Narrows)
Paper plant dumped tons of Hg into the river decades ago, causing debilitating health problems
What can we do
Stop using coal/fossil fuels as energy
Stop using products with mercury
Mercury pollution prevention
Phase out waste incineration
Remove mercury from coal before it is burned
Switch from coal to natural gas and renewable energy resources
Mercury pollution control
Sharply reduce mercury emissions from coal-burning plants and incinerators
Label all products containing mercury
Collect and recycle batteries and other products containing mercury
What to do in the meantime
Watch fish consumption
Lead
Mined from lead sulfide
Found near zinc ore deposits
Toxicity of lead
Neurotoxin
Can also cause blood disorders
Inhaled or ingested
Induces oxidative stress that can damage DNA and enzyme function
Lead accumulates in what tissues
Blood
Soft tissues
Bone
Teeth
Where is most sensitive to lead
The brain
Lead causes
Intellectual disabilities and reduced brain size
