Introduction to Metals Flashcards
What functions do metals serve in biology?
- Easily donate and accept electrons
- Form water soluble cations through electron loss
- Perform essential biological functions
- Electron transfer
- Redox reactions
- Electrochemistry and signaling (Ex: Na, Ca, K)
- Structural (Ex: Ca in bone)
What are the toxicity mechanisms of metals?
- Oxidative damage (Zn)
- Altered electrophysiology and osmotic states (Na)
- Competition with normal elements for absorption (Mo/Cu)
- Incorporation into proteins in place of normal constituents (Pb/Ca)
What metals are of the highest concern for veterinarians?
- Lead
- Copper
- Zinc
- Sodium
- Iron
- Arsenic
What is a metal?
- A chemical element whose atoms readily lose electrons to form cations, and form metallic bonds between other metal atoms and ionic bonds with nonmetal atoms
- Exist as elements or compounds
`What is a heavy metal?
- Poorly defined subset of elements tat exhibit metallic properties
- Relatively toxic (Pb, Sn, Hg, Tl, Au, Pt, Ba)
- Considered meaningless by IUPAC
What are the toxicological properties of heavy metals?
- Cumulative in biological systems
- Can change valence
- Complex with organic molecules
- Persistent in the environment
- Can be strong oxidants
- Bind to essential molecules
- Many metal to metal interactions
- Clinical toxic effects vary widely
What are the oxidation states of heavy metals?
- Multiple states
- This lead to the formation of different compounds having different toxicological properties
What elements form covalent bonds with heavy metals?
- Sulfur, oxygen, and nitrogen
- Can be basis for toxicity
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What animals are commonly affected by lead poisoning?
- Cattle
- Dogs
- Cats, Pet birds, zoo animals
- Sporadically hoses and sheep
- Pigs are resistant
What are the major effects of lead?
- Nervous system is the primary target
- Mild irritant to GI mucosa
- Anemia due to interference with RBC maturation
What are the sources for lead?
-
Lead carbonate used to be a common component of paint
- Strictly controlled since the 1970’s
- Old buildings/ stored paint remain important sources
- Lead-acid Batteries
- Industrial/mining pollution
- Lead shot, bullets
- Lead weights
- lead sinkers
- lead toys
- Motor oil form leaded gas engines
- Old grease
- Old linoleum
- Pollution
What are the important kinetic factors of lead?
-
More surface area = more absorption
- Lead/acid battery plates
- GIT mucosal surface area
-
Acidic environment = more absorption
- low pH leads to ionization
-
More time = more absorption
- lead particles may be trapped in the reticulum
What is the half-life of lead in various tissues?
- Blood - a few days
- Liver/kidney - weeks
- Brain - months
- Bone - >1000 days (practically a lifetime burden)
What is the common signalment for lead poisoning?
- Seasonal incidence - spring, early summer
- Age - often younger animals (pups, calves)
- Locations:
- Dogs - older homes, low income areas, work places
- Cattle - casual management, old buildings, junk piles
What are the Toxicokinetics of lead
- Ingested lead typically requires solubilizing
- Acidic environment of stomach vs. lead in soft tissue
- Poorly absorbed - ~2% from GI tract
- Dust inhalation - fine particles < 0.5 um
- Tissue binding - first to erythrocytes
- 90% binds to RBC, some to albumin
- Crosses blood-brain barrier and placenta - embryo toxicity
-
Incorporation into bone:
- storage site, detoxification mechanism
- Lead line - in radiographs, in gums
How is lead eliminated from the body?
- Fecal
- Urinary
What are the acute toxicity amounts of lead?
(Calves, cattle, dog, horse, ducks geese)
- Calves - 40-600 mg/kg
- Cattle - 600-800 mg/kg
- Dog - 191-1000 mg/kg
- Horse - 500-750 mg/kg
- Ducks - 18 pellets of #6 shot
- Geese - 25 pellets of #6 shot
What are the chronic toxicity amounts of lead?
(Calves, cattle, dog, horse, ducks geese)
- Calves - none (would be adults)
- Cattle 1-7 mg/kg
- Dog 1.8-2.6 mg/kg
- Horse 2.4-7 mg/kg
- Ducks 2 mg/kg
- Geese - unknown
What is the MOA of lead?
- Binding to sulfhydryl groups
- Heme synthesis ⇓
- Altered GABA transmission
- Competition with divalent cations Ca++ ions
- Displace Ca++ from binding proteins
- Altered nerve and muscle transmission
- Inhibition of membrane associated enzymes
- Calmodulin, Na./K pumps
- Altered vit D metabolism
- Impaired Ca++ absorption & Zn related enzymes
What is the clinical presentation of lead toxicosis?
- Clinical onset usually delayed several days
- Time for absorption, binding to active sites
- Depends on form of lead
- Organic: rapidly absorbed and distributed
- Metallic: slower absorption & onset
- Carbon, nitrate, oxide salts > acetate & chloride salts
What are the clinical signs of lead toxicosis in most species?
- Onset = several days after exposure
- Signs quite variable: slow vs explosive
- GI + Neurologic combo
- Complete anorexia
- CNS depression / Convulsion
What are the clinical signs of lead toxicity in Dogs?
- GI: vomiting, anorexia, tender abdomen, diarrhea/constipation
- usually appear first
- CNS: lethargy, hysteria, convulsions, ataxia, blindness, mydriasis
What clinical pathology is found in dogs with lead toxicosis?
- Increased nucleated RBC’s and basophilic stippling without severe anemia
What are the differential diagnosis for lead toxicosis in dogs?
- Canine distemper
- Parasites
- Methylxanthines
- Tremorgenic mycotoxins
- NSAIDs (GI)
- Salt toxicosis
What are the clinical signs of lead toxicosis in cats?
- Less common due to eating habits
- Lethargy
- Anorexia
- Vomiting
- Weight loss
- Excessive salivation
- Neurologic signs can be minimal
What are the clinical pathology findings in cats with lead toxicosis?
- Inconsistent nucleated RBC’s and basophilic stippling
- Elevated AST, ALP
What are the differential diagnosis for cats with lead toxicosis?
- Organophosphates
- Bromethalin
- methylxanthines
- Hepatic encephalopathy
What are the clinical signs of lead toxicosis?
- GI: anorexia, rumen stasis, gaunt, salivation
- CNS: blindness, muscle twitching, head bobbing, depression, bruxism, circling, convulsions
- Acute convulsive death in calves
What are the differential diagnosis for cattle with lead toxicosis?
- Water deprivation
- Polio
- Organophosphates
- nervous coccidiosis
- Rabies
What are the clinical signs of Birds with lead toxicosis?
- Depressed
- Weak
- Anorectic
- weight loss
- esophageal paralysis
- regurgitation
- diarrhea
- Wing droop
What are the clinical signs of lead toxicosis in horses?
- Recurrent laryngeal nerve paralysis results in “roaring”
- Ataxia, incoordination
- Foals - metaphyseal sclerosis
What is the gross pathology of lead toxicosis in cattle?
- Lead objects in rumen or stomach
- Rumen protozoa dead or inactive
- Laminar cortical necrosis (DDx from PEM)
- Inconsistent acidophilic intra-nuclear inclusions in renal tubules
- Porphyrinuria