Introduction
● Zinc phosphide is a fine black crystalline powder and commonly used as rat poison.
● It has garlic odour or has a repulsive odour of rotten fish.
● Recently, human poisoning by Zinc phosphide has increased tremendously.
● Being a fine powder it adheres in the crypts and cavities of the stomach and is not completely eliminated through vomiting. Death may ensue from the liberation of phosphide from the adhered materials.
It is marketed under various trade names includes Agrophos, Commando, Sudarshan, Ratoff, Ratol, Robart, etc.
Uses
- It is used as rodenticide.
- It is also used to preserve grain.
Fatal Dose
The fatal dose of zinc phosphide is about 2 to 5 grams.
Fatal Period
The fatal period of zinc phosphide is 24 hours.
Mode of Action
● Zinc phosphide liberates phosphine when it comes in contact with air and moisture.
● It reacts with acidic media (HCL) of stomach and release phosphine gas, which is rapidly absorbed from gastrointestinal tract by simple diffusion.
● Phosphine is a protoplasmic poison interfering with enzymes and protein synthesis.
● In animal studies, phosphine has been shown to cause non-competitive inhibition of cytochrome oxidase of myocardial mitochondria.
Sign and Symptoms
- Metallic taste
- Garlicky or fishy odour of breath
- Vomiting
- Intense Thirst
- Burning sensation
- Massive focal myocardial injury.
- Pain in abdomen
- Diarrhea
- Persistent hypotension with shock
- Dyspnea
- Cough
- Tachycardia
- Tachpnea
- Bleeding diathesis
- Restlessness
- Altered sensorium
- Coma
- Respiratory distress.
- Substernal pain
- Convulsions
- Hepatic damage
- Renal failure
- Coagulation failure
- Metabolic acidosis
- Death
Treatment
● Secure airway, oxygen, ventilator assistance should be given.
● Manage shock with intravenous fluid and inotropic support.
● Manage metabolic acidosis with sodium bicarbonate.
● Magnesium sulfate administration remains controversial. It is said that administration of magnesium sulfate is beneficial for management of cardiac arrhythmias.
● Gastric lavage is contraindicated since administration of water will release phosphine from the available zinc phosphide in the stomach.
● Ranitidine 50 mg IV 8th hourly is administered to reduce the severe epigastric pain.
● Control of convulsions with anticonvulsants such as benzodiazepines, barbiturates, etc.
Post Mortem Findings
- Typical garlicky odor.
- Congested organs
- Bright fluid blood
- Pleural effusion
- Pulmonary edema
- Toxic myocarditis
- Bleeding diathesis
- Gastric mucosa shows shedding.
- Kidney shows acute tubular necrosis.
- Liver shows fatty change.
- Hypoxic organ damage with congestion and petechiae.
- Inflammatory infiltrate in portal tract and centrizonal necrosis.
- Heart may shows features of toxic myocarditis with fibrillar necrosis.
Test of Detection and Forensic examination
- Garlicky smell in the breath.
- Altered liver function tests with raised transaminase levels.
- ECG sinus tachycardia, ST depression in leads II and III.
- Urinalysis may reveal occult blood, bilirubin, glucose, and albumin.
- Blood urea and serum creatinine are usually higher than normal.
Qualitative tests for detecting phosphine in the breath and gastric aspirate-
Silver nitrate test or Breath test – The patient is asked to breathe through a piece of filter paper impregnated with 0.1 N silver nitrate solution for 5 to 10 minutes. If filter paper becomes black, it indicates the presence of phosphine. The blackening is imparted because phosphine reduces silver nitrate to silver. Similar reaction is also produced by hydrogen sulfide.
Biological sample test: A small amount of gastric apirate (5 to 10 ml) or minced tissue (5 to 10 gm of liver) is taken into a steam distillation flask to which an equal quantity of water is added and then acidified with dilute HCl or H2 SO4, followed by heating upto 500 C for 15 minutes. The distillate is collected in an ice cold receiver containing 5 ml of 1% silver nitrate solution by dipping the adapter into it. If phosphine is present, the solution will turn black.
For confirmation, add 5 ml of concentrate.HNO3 to the black precipitate and boil till the solution becomes clear. Then add 5 ml of ammonium molybdate solution and heat for a minute. Formation of a yellow precipitate confirms the presence of phosphine.
A variation of this test involves placing 0.1 N lead acetate filter paper over the mouth of the distillation flask containing the sample (prepared in the same manner as detailed above). The flask is heated for 15 minutes at 500 C. Phosphine will blacken the silver nitrate paper, while hydrogen sulfide will blacken both papers.
Others
- Gas chromatography
- Thermionic nitrogen-phosphorus detector
- Flame photometric detector
Medico Legal Aspects
● Accidental and suicidal poisonings have been reported involving the consumption of rat pastes containing zinc phosphide.
● Some of these brands are marketed in tubes that look very similar to toothpaste tubes leading to accidental use.
References
- Dr. K.S. Narayan Reddy. The essential of forensic medicine and toxicology.34th edition.
- VV Pillay. Modern medical toxicology.4th edition.
- R.K.Sharma. Concise textbook of forensic medicine and toxicology. 3rd edition.
