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
How is Lead toxicosis diagnosed?
- History, clinical signs
- Lead in whole blood
- >0.35 ppm (0.25 avian)
- Normal = < 0.05 ppm
- Lead in Kidney or Liver
- >8 ppm
- Normal = <0.5 ppm
- Radiography- Lead objects in gut
-
Peripheral blood smear (dogs)
- nucleated RBC’s, basophilic stippling
- Ca-EDTA mobilization test
- Urinalysis: increased delta aminolaevulinic acid (ALA), Lead concentration
What is the treatment for lead toxicosis?
(Broad sense)
- Remove animal from source
- Stop further absorption
- Increase excretion-chelators
- Supportive care
How can further absorption of Lead be stopped?
- Decontaminate GI tract
- cathartics, enema according to species
- Endoscopy or gastrotomy to remove objects
- Oral MgSO4 in cattle (laxative and formation of insoluble PbSO4
- Charcoal NOT effective for metals
What Chelators are used for lead toxicosis treatment
- CaEDTA - IV/SQ
- standard for cattle - FDA restricts use
- D penicillamine - PO in SA
- Succimer
- DMSA (dimercaptosiccinic acid) Chemet, Bock (PO in SA)
- Approved (dogs) 20mg/kg TID for 5 days then BID for 2 weeks
- Effective in cattle, dosage and expense preclude
- DMSA (dimercaptosiccinic acid) Chemet, Bock (PO in SA)
What is the supportive care for lead toxicosis?
- Fluids, thiamine
- Control seizures: valium, pentobarbital+/-
- Mannitol, dexamethasone for cerebral edema
- Antioxidants (Vit C, E): N-acetylcysteine
- Good nursing care
What are the public health concerns with lead?
- Children in household exposed to the same lead source as pets
- Food safety:
- long residue time in bone
- transfer to milk in early lactation
- Residues can vary from weeks to months
- Contact state veterinarian recommended
What is Arsenic (As)?
- Metalloid
- Elementa, organic, and inorganic
- Trivalent (+3) comes as organic and inorganic
- Pentavalent (+5) comes as organic and inorganic
What are the sources of Arsenic?
- Mining sites and smelters
- Insecticides and herbicides
- Wood preservative
- Medicinal (heartworm therapy)
- feed supplements
What are the sources for inorganic Arsenic?
- Old pesticides - Lead arsenate, herbicides
- Terro ant poison
- Ashes of Chromated Copper Arsenate (CCA) lumber
- common source for cattle
What are the Toxicokinetics of Arsenic?
- Absorption of different forms is variable
- major toxicity factor
- Distribution:
- Accumulation initially in liver and then slowly distributed to other tissues (ie spleen, liver, lung) later accumulates to keratinized tissue
- Crosses placenta and is embryotoxic
- Crosses blood-brain barrier
- Hair and keratinized tissue - eliminated in the feces and urine
What are the toxic mechanisms of inorganic Arsenic?
- Binds with sulfhydryl enzymes
- Blocks cellular respiration
- Acts on tissues with high respiration
- Gut epithelium, capillaries
- Acts on tissues with high respiration
- Phosphate competition - uncouples oxidativephosphorylation
- Toxicity: trivalent is 5-10x more toxic than pentavalent
- Arsenite (+3) > Arsenate (+5) > organic As
-
Arsenite- inhibits ATP synthesis
- sulfhydryl inhibition (enzymes)
- a-lipoic acid - TCA cycle
- Arsenate- resembles Pi in structure and reactivity, replaces phosphate
What Arsenic was used in Heartworm therapy and what are the effects?
- Thiacetarsamide - Caparsolate
- Vomiting
- Liver and kidney damage
- Ivermectin, melarsomine (melaminylthioarsenate) and Diroban (melarsomine HCL) commonly used now
What are the GIT clinical signs of inorganic Arsenic toxicosis?
- Vomiting
- Intense abdominal pain
- Diarrhea (+/- blood)
- Fluid loss
- Maybe acute death (hours)
- Marked dehydration
- Weakness, staggering gait
What lesions are common with inorganic arsenic toxicosis?
- GI hemorrhage, edema, fluid filled
- Sloughing, mucosa
- Renal tubular degeneration
How is inorganic arsenic toxicosis diagnosed?
- Arsenic analysis of kidney, liver >8ppm
- Suspect material
- Urine contains As if kidneys are functioning
- Accumulates in hair for chronic exposure
- Blood is NOT a good diagnostic source
What are the treatment options for inorganic arsenic toxicosis?
- Most attempts are futile
- Rehydration
- BAL (dimercaprol) is classic antidote, best before signs
- Thiotic acid 50mg/kg q8hr
- Succimer (DMSA)
What is Iron (Fe)?
- Common in human dietary supplements and vitamin/mineral tablets
- Ingestion of concentrated Fe sources can be toxic to children and pets
- Injections can be toxic
What are the levels of toxicity of Iron?
- Non toxic <20 mg/kg
- Mild-Moderate 20-60 mg/kg
- Serious >60 mg/kg
- Life threatening >200 mg/kg
What are the 4 stages of clinical effects of Iron toxicosis
- 0-6hr: Corrosive effects
- nausea, vomiting, diarrhea, GI hemorrhage
- 6-12hr: Apparent remission
- 12-24 hr (in severely poisoned dogs)
- Severe lethargy
- Reocurrance of GI signs
- Metabolic acidosis
- Liver necrosis
- Coagulopathy
- Cardiovascular collapse, shock
- Several weeks later:
- scarring and stricture of GI tract
How is Iron toxicosis diagnosed?
- History, Clinical signs
- Abdominal radiograph
- mass of pills in stomach
- Serum Fe:
- normal 80-249 ug/dL
- 300-500 ug/dL monitor
- >500 chelation therapy
- If serum Fe>TIBC = poison likely
- (Total iron binding capacity)
What is the treatment for iron toxicosis?
- Emetic in alert animal, gastric lavage or gastrotomy
- NOT CHARCOAL
- Fluids, electrolytes, A/B balance
- GI protectants
- Chelation therapy:
- Deferoxamine (Desferol)
- Initial IV infusion - 15 mg/kg/hr
- IM 40 mg/kg q 4-8hr
- Continue until serum Fe is below 350 ug/dL
What is Mercury (Hg)?
- Toxicosis is infrequent and sporadic
- in last 30 years are associated with Hg fungicide treated seed
- Unusual metal because it is a liquid at normal temperatures
- Hg vapor poses a substantial hazard
- 3 different forms in the environment
- Elemental Hg, Hg0- metallic or vapor
- Inorganic mercury, Hg Salts HgCl2
- Organomercurial compounds,
- alkyl forms = ethyl, methyl, propyl, dimethyl, etc, and aryl forms of Hg such as phenylmercuric acetate
- Hg accumulates as alkyl, methyl, and ethyl mercury
What are the sources for Mercury?
- Batteries
- Some pharmaceuticals -
- calomel - antiseptic salve, in laboratory electrodes and as a fungicide
- Industrial effluents, sewage sludge
- Ocean waters - marine fish, shell fish, mackerel, shark, swordfish, tilefish, tuna
- Thermometers, barometers fluorescent tube
What are the toxic levels of Mercury?
- Elemental Hg is low in toxicity orally
- Hg salts: 1mg/kg/day is toxic to cats in 15 days
- Hg salts: large animals 8-12 mg/kg
- Methyl (alkyl) mercury 0.2 - 0.5 mg/kg
- Phenyl (aryl) mercury - Swine 1 mg/kg
- Highly toxic on a chronic basis
What are the clinical effects of inorganic mercury?
- Gi and renal tubular necrosis
What are the clinical effects of organic mercury?
- Crosses BBB and Placenta
- Neurologic fibrinoid degeneration of arterioles
- neuronal necrosis ⇢ blindness, staggering, incoordination, recumbency, death
How is mercury absorbed?
- Elemental Hg poor GIT absorption
- Vapors are absorbed and dangerous
- Salts and organ mercurial are absorbed in the GIT
How is Mercury excreted?
- Kidney ⇢ urine
- Fecal
- Lungs
What are the mechanisms of toxicity of Mercury?
- Primary targets are the kidneys and CNS
- Bind to sulfhydryl groups
- Inhibit enzymes and protein synthesis
- Inhibit mitochondrial function by binding to alpha lipoic acid and thioctic acid
- Sulfur containing organic acid cofactor involved in aerobic metabolism
- Pyruvate dehydrogenase complex (PDC)
How is Mercury toxicosis diagnosed?
- Whole blood > 1ppm
- Liver
- Kidney
- Hair
- Urine
- Feeds
How is Mercury toxicosis treated?
- Acute exposure:
- Egg white, activated charcoal, sodium thiosulfate (0-1 g/kg)
- Saline cathartic or sorbitol
- Oral penicillamine (1-50mg/kg) orally
- DMSA
- Chronic organic exposure: selenium and Vit E
What risk does mercury pose to public health?
- Bioaccumulation & bio magnification in the food chain
- sediments ⇢ fish ⇢ mammals
- Mercury residues in kidney & muscle tissue
- highest concern in fish - (0.7 - 1.5 ppm)
What is Thallium (Tl)?
- Discovered in 1861 Sir William Crooks
- Elementary Tl is Non-toxic
-
Monovalent and trivalent salts are very toxic
- Thallous - +1 oxidation state
- Thallic - +3 oxidation state
- Heavy metal - very toxic and highly cumulative
Sources of thallium?
- World production is 12 tons/yr
- Semiconductors, photocells, optic glass, thermometers
- Tl201 radioactive tracer used in heart scintigraphy to detect myocardial ischemia
- Rodenticides
What is the MOA of Thallium?
- Blocks energy utilization by Na-K-ATPase channel
- blocks active transport of K across the cell membrane
- Similarities in charge between K+ and Tl
- Tl has a 10x greater affinity than K+ in neuronal, cardiac, and skeletal muscle cells
- Half-life of 30 days
- blocks active transport of K across the cell membrane
- Blocks energy production from glucose
- ADP to ATP by pyruvate kinase - K requiring enzyme
- Tl binds with 50x affinity compared to K+
- ADP to ATP by pyruvate kinase - K requiring enzyme
- Damages riboflavin, forming an insoluble complex and intracellular sequestration of vit B6
- Binds to SH groups and interferes with formation of disulphide bonds in keratin, structural damage to hair and nails (depilatory)
- Causes activation or inhibition of other enzymes
- ALA synthetase, B12 metabolism
What are the clinical effects of thallium toxicosis?
- Multisystemic disease
- GI necrosis - sever hemorrhagic gastritis, congested oral mucosa
- Neurologic - trembling, motor paralysis, mental retardation
- Alopecia and skin sloughing from 7 days to 2-3 weeks after ingestion, renal and liver injury
- Blindness
How is Thallium toxicosis diagnosed?
- Urine thallium (any concentration is significant)
- Kidney
- liver, feces
What is the treatment for Thallium toxicosis?
- Radiogardase - prussian blue insoluble capsules
- ineffective once clinical signs are apparent
- Dithizon - chelator for Thallium
What is Fluoride?
- Reactive, water soluble non-metal
- Common in nature, variable in distribution
What are the sources for fluoride?
- Mining deposits
- Rock phosphates (feeds)
- Water from deep wells/geothermal water
- Industrial pollution (particles may settle on pastures)
- Production of industrial processing of aluminum ores or phosphate fertilizers
- fertilizers and calcium phosphate minerals must be defluorinated
- Pesticides
What are the _______
- Affects mineralized tissue
- teeth bone
- Deposits in hydroxyapatite crystal of bone and distorts normal Haversian system remodeling
- Dental fluorosis is dystrophic formation of dentin and enamel in erupting teeth only (marker for time of exposure)
What are the clinical effects of fluoride toxicosis?
- Chronic exposure:
- Progressive debilitating disease
- Cattle, horses, wild herbivores
- Osteofluorosis:
- Bone formation on outside of long bones (exostoses)
- produces lameness
- Bone formation on outside of long bones (exostoses)
- Dental fluorosis:
- Softening of tooth enamel, early wear
What are the kinetics of fluoride?
- Rapidly absorbed
- Excreted through urine
- some through milk
- ~50% absorbed dose sequesters in bone
- Mostly in developing/remodeling bone
- Developing teeth - erupted teeth unaffected
What is the clinical picture of Fluoride toxicosis?
- Large, acute exposure:
- GI irritation and kidney damage
- Moderate/Chronic exposure:
- more common
- affects bones and developing teeth
- Osteogenesis is interrupted/altered
- Prominent effects seen in long bones, mandibles and rib surfaces
- Articular surfaces are NOT affected
- Spurring around joints produce pain and lameness
- Abnormal postures, stiffness, disinclination to move, weight loss
How is Fluoride Toxicosis diagnosed?
- History, clinical signs, lesions
- Feed, mineral, and water analyses
- Biopsies of coccygeal vertebrae or ribs
- Urine fluoride may be helpful within 1-3 weeks of exposure
- kidney and liver can be tested postmortem
What are the clinical signs of fluoride toxicosis?
- Lameness
- weight loss
- elongated hooves
- lapping water
What are the common lesions seen with fluoride toxicosis?
- Dental fluorosis in erupting teeth
- Exostosis of limbs, ribs, mandible
- Fl analysis:
- Urine (15-20 ppm) - recent
- bone (>3000 ppm) - prolonged exposure
What is the treatment for Fluoride toxicosis?
- No specific treatment
- poor prognosis
- Pain management and soft feed may allow salvage following extended recovery periods
- Avoid exposure
- Aluminum or Ca-carbonate at 1% of diet will reduce fluoride absorption