oxalic acid and its salts are used in industry as bleaching agent and in calico printing

Its household use for bleaching has made it a dangerous substance

Solutions containing oxalic acid cause falling off hair when poured on the head

Oxalic acid is sometimes used to erase writing in attempts at forgency

Lecture on oxalic acid

Prepared by Dr. Amina Rao

K.M.S Medical College ,Sialkot

Difference between organic and inorganic acids

Organic acids differ from inorganic acids in two major respects:

1) They are weaker in action 2) They are usually absorbed into

circulation and so have both local and remote action

organic acid• Important poisons are oxalic, carbolic,

acetic and salicylic acids.• They have powerful rapid action • They act as strong irritants locally and

also possess a powerful remote action after absorption

Oxalic acid Oxalic acid is a corrosive acid.Oxalic acid is a constituent of many house

hold products. It is found in many disinfectants, household bleach, metal cleaning liquids, antirust products and furniture polishes.

Oxalic acid is found in several green leafy vegetables such as spinach, rhubarb, Brussels sprouts, broccoli, carrots , cabbage lettuce etc. It also occur in fruits such as berries , concord grapes, figs, and plums etc. along with in some seeds, nuts and grains.

physical appearanceoxalic acid is crystalline substance resemble in appearance with magnesium sulphate and zinc sulphate. It can be differentiated as features oxalic acid mgso4 znso4

ncetaste Sour and acidic

Bitter and

nauseating

Bitter and

metallic

reaction Strongly acid

neutral

Slightly acid

Heat sublimes Not so Not so

Sodium carbona

teEffervescence but

no ppt

No effervesce

nce but white ppt

No effervesce

ncebut white ppt

Ink or iron stain

bleaches Not so Not so

Signs and symptomsThe character and severity of symptoms depend upon the amount and conc. Of acid taken.

it has two distinct effects 1. Local effect2. Remote effecte.g. shock, hypocalcemia and renal damageA. Local effect: It readily corrodes the mucous membrane Of the

alimentary tract but rarely the skin.

REMOTE EFFECTA large concentrated dose would kill with in

a couple of hours by shock or hypocalcaemia (lowering of calcium levels in the blood).

A large dilute dose would cause kidney failure

Large doses causes rapid death from shock(narcotic effect).• There is a sour taste in the mouth and burning

sensation in throat and stomach.• This is followed by persistent vomiting. Vomit is

black in color (coffee ground)due to altered blood

If in a case of short duration, the intestinal tract is not affected but when life is prolonged

There is pain and tenderness over the abdomen, purging and tenesmus may appear after absorption, collapse may occur.

Oxalic acid in circulation react with free Ca in plasma to form Ca oxalates crystals causing dec. in free Ca in plasma inducing hypocalcaemia. Numbness and tingling indicate the effects of hypocalcaemia on the nervous system. Spasmodic twitching of the muscles of the face and extremities and even convulsions may be followed.

oxalic acid has a nephrotoxic action and irritation of kidneys may be found

There may be oliguria and urine contains albumin, blood and Ca oxalate crystals.

Presence of oxalic acid crystals in the urine is termed as oxaluria

Precipitation of calcium oxalate in the renal system (proximal tubules of the kidney) may lead to local necrosis of the tubular epithelium, producing kidney dysfunction and electrolyte imbalance. In renal tubular injury the path physiological factors at the cellular level are considered to be energy depletion, cell swelling, calcium influx, intracellular acidosis and enzyme activation . Obstruction of the renal tubules by the crystals is also a mechanism of renal damage

Fatal DoseThe average fatal dose of the poison is about 15-20gmsthe smallest recorded fetal dose is 5 gms

Fatal Period Death usually occurs within an hour.The longest recorded period is 5 days.

Treatment 1 Gastric Lavage wash the stomach using limewater. A soft stomach tube can be passed with care. Warm water should not be used as it dissolve more acid.2. Antidote Antidote is any Ca preparation which convertsthe poison into insoluble Ca oxalates.A suspension of 30gms of chalk in water or milk will neutralize about 20gms of oxalic acid.Alkalis such as soda, potash and ammonia should not be given as their oxalates are insoluble

Ca Gluconate may be given by mouthOr 10ml of a 10% solution intravenouslyIn severe cases, parathormone extract Should be givenThe rest of the treatment is symptomatic.

example A 50 years old woman swollen about 30gms of

oxalic acid in beer. In half an hour, she complained of burning

pain in stomach and was found rolling about. Chalk and water was freely given and she recovered

Postmortem appearance

• The mucous membrane of the tongue, mouth, throat is commonly white as if bleached but is sometimes reddened by irritation. Lips and chin don’t show staining

EFFECTS ON STOMACHo The stomach contains a dark brown gelatinous

liquid due to the formation of acid haematin.o The mucous membrane is corroded and

detached in varying degrees depending upon the conc. Of acid

Perforation however is rare. The blood vessels in submucosa layer may be seem distinctly as dark lines due to acid haematin. The outer coat of the stomach may be inflamed.

If the effect are only narcotic, there will be congestion of lung, liver, kidney and brain without any local changes where death has been delayed. Inflammation will be found on the upper portion of the small intestine and the kidney.

Medicolegal aspectsAccidental poisoning is due to being mistaken for

MgSO4 or sodium bicarbonateOxalates occur in the leaves of rhubarb and have

caused poisoning when the leaves are used as safe vegetables

Oxalic acid is sometimes taken with suicidal intention but rarely used for homicide on account of its sour taste and rapid action

oxalic acid and its salts are used in industry as bleaching agent and in calico printing

Its household use for bleaching has made it a dangerous substance

Solutions containing oxalic acid cause falling off hair when poured on the head

Oxalic acid is sometimes used to erase writing in attempts at forgery