Phosphoric Acid - Corrosive(Caustic) Poisons

Phosphoric Acid

Physical Appearance

Phosphoric acid is a clear, colourless, odourless, unstable, orthorhombic crystalline solid, or a syrupy liquid with a pleasing acid taste (when suitably diluted).

Uses

·     Phosphoric acid is used as a flavouring material, an acidulant, and a synergistic antioxidant and sequestrant in carbonated beverages.

·     Phosphoric acid is also utilised in dental ceramics, for water treatment, in engraving processes, for the rust-proofing of metals prior to painting, for metal pickling, in the coagulation of rubber latex, and as an analytic reagent in laboratories.

·     Dilute phosphoric acid has been used in preparations for the management of nausea and vomiting, and in Great Britain, a technical grade of orthophosphoric acid in water, 1:330, is an approved disinfectant for foot-and-mouth disease.

Usual Fatal Dose

About 300 to 500 ml.

Clinical Features

·      Corrosion of GI tract, sour acrid taste, vomiting, abdominal pain, bloody diarrhoea, acidosis, convulsions, coma, death.

·      Hyperphosphataemia and hypocalcaemia are common find-ings. There may also be hypomagnesaemia.

Diagnosis

Add 2 ml of ammonium molybdate solution, followed by 1 ml of nitric acid to a small quantity of gastric aspirate and heat for 1 minute. A canary yellow precipitate is specific for phosphoric acid.

Treatment

On general lines, as for other corrosives, (see under “Sulfuricacid”). Convulsions can be managed with benzodiazepines orbarbiturates. Hyperphosphataemia (if severe) can be treated by haemodialysis.