(F) 19 - Heavy metals Flashcards
Mercury: toxicity, negative effects, solutions to reduce their impacts
Toxicity and Negative effects
- mercury is a neurotoxin and teratogen
- increases oxidation and oxidative damage in the body, especially the brain
- exposure to mercury in pregnancy can cause severe birth defects
Solutions
1. Prevention
- phase out waste incineration
- remove mercury from coal before it is burned
- switch from coal to natural gas and renewable energy resources
- 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
How do most instances of mercury poisoning occur?
Due to contact with organomercury, and particularly methylmercury
Why is methylmercury so toxic?
- readily absorbed by the digestive tract of humans, as opposed to other forms of mercury
- from there it can be easily transported across the blood-brain barrier, and across the placenta
- WHY? it binds with the AA L-cysteine. The body then mistakes this methylmercury-L-cysteine complex for another necessary AA, L-methionine
Lead: toxicity, negative effects, solutions to reduce their impacts
Toxicity
- like mercury, lead is a neurotoxin; can also cause blood disorders
- inhaled or ingested
- induces oxidative stress that can damage DNA and enzyme fxn
- bioaccumulates in: blood, soft tissues, bone, teeth
- brain is most sensitive to lead
Negative effects
- intellectual disabilities and reduced brain size
- affects childrens’ health; smaller body = reach relative concentrations faster
Solutions
1. Prevention
- replace lead pipes and plumbing fixtures containing lead solder
- phase out leaded gasoline worldwide
- phase out waste incineration
- ban use of lead solder
- ban use of lead in computer and TV monitors
- ban lead glazing for ceramicware used to serve food
- wash fresh fruit and veg
- Control
- remove leaded paint and lead dust from older houses and apartments
- sharply reduce lead emissions from incincerators
- remove lead from TV sets and computer monitors before incineration or land disposal
- test blood for lead by age 1
- test for lead in existing ceramicware and used to serve food
- policies = effective
What are the 3 problems with heavy metals?
- Associated with particulate matter, easily transported in the atmosphere
- Toxic, even in low concentrations
- Can bioaccumulate
Common forms of Hg (with chemical formulas) and overall Hg cycle
- Elemental mercury (Hg0)
- can be mixed with other metals (copper, gold, silver) to form alloys called amalgams - Inorganic mercury (mostly Hg2+)
- ionized mercury, ions with a 1+ (rare) or 2+ charge - Organomercury (mostly MeHg+)
- highly toxic (but not all forms bioaccumulate)
- compounds and ions of mercury, especially organomercury compounds, are more toxic than elemental mercury
- it’s readily absorbed through skin and is bioavailable to organisms (as opposed to elemental and inorganic mercury)
- common forms: METHYLMERCURY, Dimethylmercury, Ethylmercury, Diethymercury, Merbromin, Tiomersal
How methylation of Hg works (what we know- including the rxns- and what we don’t fully understand yet)
- Ionized mercury (Hg2+) in seawater and sediments cannot enter bacterial cells
- With little or no O2 available, some bacteria use sulfate (SO42-) for respiration, expelling sulfide (S2-) as a waste product
- Sulfide combines with ionized mercury (Hg2+) in seawater to form mercuric sulfide (HgS), which can diffuse into bacterial cells
- Inside bacterial cells, a methyl group (CH3) replaces the sulfide to produce monomethyl mercury (CH3Hg or MMHg) which diffuses into seawater and is taken up by phytoplankton
SO42- —>S2-
S2- + Hg2+ —> HgS
HgS + ? —> CH3Hg
Example of methylmercury poisoning: the Minamata Disease
What?
- First big incident of large scale mercury poisoning; how we learned about its toxicity and impact on organism (including us) health
- Minamata had 2 big industry plants, for fishing and chemical production respectively
- Methylmercury in wastewater from Chisso Corporation factory; mercury used as a catalyzer to produce acetaldehyde; byproduct was metal mercury that was dumped into the bay = Minamata Disease
How did they accumulate so much mercury?
FISH
- ppl didn’t fully methylmercury readily bioaccumulate and biomagnifies
Example of lead poisoning: how/why Pb contaminated drinking water during the Flint Water Crisis
*Lead bioaccumulates but it doesn’t biomagnify very well. Scavengers and fish can experience lead poisoning.
What happened?
- City of Flint swapped drinking water source to the Flint river to save money. Needed to add extra CHLORINE. Gov said there was nothing to worry about but eventually instructed to get lead blood testing.
- Scientists alert that corrosiveness of water from Flint River may leach lead out of city pipes so additives are used to control corrosion from chlorine. Additional corrosion controls used and city declares state of emergency.
- Orthophosphate decreases corrosion; chlorine increases corrosion
- more lead = more iron (rusty H2O) = BAD
3 ways to reduce lead exposure and lead pollution
- Don’t use products containing lead
- and if you do, dispose of them properly - Remove (or advocate for the removal of) lead pipes and paint
- Advocate for environmental remediation at sites with lead contamination
