Inorganic Poisons

Arsenic

• there are inorganic and organic forms

• can cause acute (GI) or chronic (CNS, kidney) signs

• valence affects toxicity

  • trivalent (As³⁺) is more toxic, pentavalent (As⁵⁺) is less toxic

• readily absorbed from GI tract, lungs, and intact skin

  • accumulates in the liver, then distributes to other tissues

• can be excreted in urine, feces, sweat, and milk

Common sources of arsenic

• herbicides/rodenticides

• antifungal agents on seed grains

• wood preservatives

• growth enhancers, medications

Which form of arsenic is the most toxic?

trivalent (As³⁺)

Copper

• an essential nutrient that can be toxic with high intakes

• species differences related to dose

  • SHEEP ARE VERY SENSITIVE → readily accumulate it and have trouble excreting it

    • >15 ppm is toxic to them

• chemical interactions and toxicity depend on Cu availability

• most consistent acute sign is liver dysfunction ± hemolytic anemia (in sheep)

  • gunmetal kidneys are a pathologic finding

• Cu is readily mobilized during times of stress

• all animal groups are at risk to Cu toxicity

Common sources of Cu

• poisoning is more likely to occur where multiple sources exist

  • feed additives

  • concentrate mixes

  • forages

  • trace mineralized salts

  • foot baths

  • medicinals

Flourine

• sources

  • soil types, mine drainage

  • rock phosphates

  • water sources

  • 1080 rodenticide (NaF)

• deposits in teeth and bones, can cause abnormal formation and mineralization by interfering with Ca

• clinical signs

  • mottle teeth

  • arthritic joints

Lead (Pb)

• acute poisoning

  • GI signs

    • poorly absorbed by GI

• chronic poisoning

  • not excreted very efficiently

  • CNS signs

  • anemia

• ruminants may be more sensitive - lead is solubilized in the rumen

Common sources of lead

• storage batteries (cattle like to lick them)

• leaded solder and lead water pipes

• lead shot used in hunting

• old lead based paints

• industrial pollution

• pollution from vehicle exhaust when leaded gasoline was in use

• lead can be persistent in the soil

Mercury (Hg)

• a cumulative poison → biomagnification in food chain (Hg levels increase the higher you go in the food chain)

• elemental mercury → inhaled → respiratory disease, neurologic issues, renal toxicity

• inorganic mercury salts → ingested → severe damage to GI tract and kidneys

• methylmercury is far more toxic

Sources of mercury

• fungicidal seed treatments

• environmental sources

• medicinals

• devices → thermometers

Where is mercury mainly a concern?

All over the U.S.; every state has at least one mercury advisory, with many northern/midwest states having a statewide advisory

Selenium (Se)

• narrow margin of safety → especially for ruminants

• acute toxicity

  • syndromes vary

  • acute respiratory, cardiovascular collapse

• chronic toxicity - “alkali disease”

  • associated with highly alkaline soil

  • hair loss

  • abnormal hoof growth

  • emaciation, roughness of coat

  • stiffness, lameness

Selenium sources

• highly alkaline soils are high in Se

• improperly mixed feeds

• accumulator plants → Astragulus spp.

• parenteral products

How does soil pH affect Se availability?

• toxic Se soils

  • very alkaline pH, low rainfall

• nontoxic Se soils

  • acidic pH 4.5-6.5

  • non-water soluble forms are bound to Fe, Al

• low Se soils

  • recent volcanic deposits

  • weathered land

Sodium Chloride

• “Salt intoxication”

• sodium chloride toxicity is mainly due to water deprivation, not excess salt intake

• CNS signs that can result in an eosinophilic meningoencephalitis

• pigs are highly susceptible

Nitrate

• nitrate is the substance, but the toxic agent is nitrite

  • nitrate is converted to nitrite by rumen microbes

• nitrite crosses the rumen wall and binds to hemoglobin, blocking O₂ from binding

  • results in methemoglobin (blood is dark and brown) and cyanosis (lack of O₂ delivery to tissues)

• nitrite can cross the placenta and bind fetal hemoglobin, causing abortions

• acute onset within 4 hours of consumption

  • early signs: anxiety, polypnea, dyspnea, rapid and weak pulse

  • advanced signs: weakness, ataxia, low exercise tolerance

Source of nitrates

• primary source is from nitrate in plants

  • accumulates in roots and lower parts of the stem

  • nitrate accumulation is higher under drought conditions

• nitrates can also be high in water (may be from fertilization runoff)

Urea

• source of non-protein nitrogen in ruminant rations

  • urea is hydrolyzed to ammonia in the rumen

  • excess ammonia can cross the rumen wall into the bloodstream and overwhelm the liver

  • ammonium ion is highly toxic to cells

• early signs: frothy salivation, blepharospasm, incoordination, weakness

• recumbency, bloat, regurgitation of rumen contents

• hyperthermia, anuria, and cyanosis just prior to death

Sources of urea and effects

• acute toxicity

  • ration formulation mistakes

  • ration deficient in energy

• chronic toxicity

  • infertility in cattle - early embryonic mortality

Prevention for inorganic toxins

• minimize the potential for exposure

• identify potential risks for the specific molecule

  • dietary formulation - Cu, Se, nitrates, Mo

  • environmental risks - Pb, As, Nitrates, Hg

  • water risks - Pb, As, NaCl, MO, F

  • therapeutics - As, Cu, Se, Hg, F

• limited therapy options (i.e. chelation), must focus on prevention of exposure

  • diagnostic testing

  • dietary evaluation