What is a toxic heavy metal?
Dense metal or metalloid that is noted for its potential toxicity, especially in environmental contexts
What are 4 elements on the World Health Organization's list of 10 chemicals of major public concern?
What characteristics must a metal have to be considered a 'heavy metal?'
Metal having an atomic weight greater than sodium (23) and specific gravity (density) > 5 g/cm3
On the health effects basis, which heavy metals are essential?
Cu, Zn, Co, Cr, Mn, Fe
On the health effects basis, which heavy metals are non-essential?
Ba, Li, Zr
On the health effects basis, which heavy metals are highly toxic and which are less toxic?
Highly toxic = Pb, Hg, Cd
Less toxic = Sn, Al
What are the 7 toxicological properties of heavy metals?
- Persistence--long residual and half-life
- Soil residence time--> 1000 years
- Acute toxicity--plants, animals, microorganisms
- Bioaccumulation and biomagnification--through food chain
- Chronic and sub-lethal effects at low conc.
- Synergistic effects
- Teratogenic and carcinogenic properties
Is lead readily degraded in the environment?
T/F: Lead is easily absorbed and metabolized
What occurs with oral exposure to lead?
Forms insoluble compounds in GIT--small amount absorbed (acidic environment)
How does the type of lead affect absorption?
Organic lead is more readily absorbed than metallic lead
What conditions favor dissolution and absorption?
What was the Flint water crisis (in a nutshell)?
- Allowable lead levels in water = 15ppb
- What comes out of faucets = 2ppb
- What came out of Flint's faucets = 13,200ppb
What is an anthropogenic source of lead toxicity?
Aerial emission from combustion of leaded fuel, batteries waste, insecticides and herbicides
What is the most common source of lead toxicosis in animals?
T/F: A thumbnail sized chip of lead-based paint may contain 50-200 mg of lead
TRUE--the lowest lethal dose in dogs is 191 mg/kg!
Sources of exposure to lead toxicity?
- Paint (old painted surfaces, fences)
- Old batteries
- Plumbing, solder, putty
- Galvanized wire
- Some linoleum, imported ceramics/pottery
- Contamination from industry (lead oxide)
- Lead shots, weights, fishing sinkers
T/F: An estimated 10-20 million birds and other animals die from lead poisoning each year in the US
Which birds are most vulnerable to lead toxicosis?
Waterfowl--can ingest spent pellets or lost fishing tackle
What can become a source of secondary lead poisoning for wild animals?
Birds shot with lead pellets and not retrieved
How common is lead toxicosis?
It is one of the most common toxicoses! Acute to chronic, Pb displaces Ca and Zn!
Why are young animals more sensitive to lead toxicosis than adults?
Greater GIT absorption and immature BBB
Which species are most susceptible?
Cattle, horses, pets, waterfowl, and pet/wild birds
T/F: Dogs are more frequently poisoned because of their indiscriminate eating habits
Which species are more resistant to lead toxicosis?
Goats, swine, and chickens
(avian plumbism or avian saturnism)
What is the most common route of lead poisoning?
How can lead be absorbed?
Dermal (poor), inhalation (rare), ingestion (oral absorption is poor, but is increased by GI acidity)
What decreases led absorption?
Calcium, zinc, or protein
What is the mechanism of lead absorption?
Absorbed by active transport using the same carrier protein as calcium
--> If patient is deficient in Ca, vitamin D, Zn, or Fe, then Pb is more readily absorbed
Which species is GIT absorption of lead greater in?
GIT absorption is greater in non-ruminants (~10%) than in ruminants (~3%)