Nitric Acid Poisoning: Signs & Symptoms, PM Appearances, Medico-Legal Importance

Nitric acid is a clear, fuming, colorless, heavy liquid and a peculiar choking odor. It is also known as azotic acid, aqua fortis, Engraver’s acid, and red spirit of nitre.

This article consists of signs and symptoms of nitric acid Poisoning, diagnosis, fatal dose, fatal period, PM appearances, tests, and medico-legal importance. 

Nitric Acid is Yellow due to the formation of xanthoproteic or picric acid. The management depends on the extent of injury caused by nitric acid poisoning.

Signs and Symptoms of Nitric Acid Poisoning

Dermal Contact and Ingestion 

• Immediate ingestion of Nitric acid causes burning pain in the mouth, epigastric pain, dysphagia, odynophagia (painful swelling), pharyngeal pain, salivation, stridor.
• It causes more eructation, greater abdominal distention causes gas formation. 
• Yellow discoloration of tissues with which nitric acid comes in contact. E.g., Crowns of teeth, gums, lips, tongue, food pipe, stomach wall, etc. 
• If nitric acid falls on clothes, it turns yellow. 

Inhalation 

• It affects the respiratory system and causes coughing and dyspnea, sneezing, and intense irritation of the throat and lungs.
• It causes suffocation, a feeling of asphyxiation, and cyanosis (bluish skin color due to insufficient oxygen in the blood).

Contact With Eyes 

• It affects the eyes and results in Lacrimation (flow of tears) and photophobia. 

Fatal Dose of Nitric Acid Poisoning

It is mostly dependent on concentration. About 8-15 ml of concentrated acid is sufficient for adults

Fatal Period of Nitric Acid Poisoning

The average fatal period of Nitric Acid poisoning is 12 to 24 hours. 

Diagnosis of Nitric Acid

• Saliva: pH tested by litmus paper. 
• Add a few drops of NaHCO3 on the stains present on the scene, clothes, etc., and produce bubbles indicating acid. 
• Arterial pH greater than 7.22 indicates acid ingestion. 
• Chest and abdominal radiographs may show signs of gastric perforation.
• Endoscopy should be performed within 12 hours, which helps determine the treatment plan and prevent injuries. 

Post-Mortem Appearances of Nitric Acid

• Orange-yellow to brown stains present on the mouth’s skin, and contact with the acid has occurred, such as hands and neck. 
• The mucous membrane of the esophagus gets softened and becomes yellow due to xanthoproteic reaction or brown due to acid hematin. 
• Mucous membrane becomes soft, friable, ulcerated, yellow in color, and walls may rarely be perforated. 
• Inhalation of nitric acid fumes causes the larynx, trachea, and bronchi to congest, and lungs become congested and edematous (swelling). 

Chemical Tests for Nitric Acid Poisoning

• Litmus Test: Suspected solution would turn blue litmus red. 
• Copper Turnings Test: Take stomach contents or vomit in a test tube, drop a small piece of copper and heat it, produce pungent dark brown fumes of nitrogen dioxide emanate if nitric acid is present. 
• Brown Ring Test: Take stomach contents or vomit in a test tube, add robust ferrous sulfate solution and sulphuric acid gently from the sides to produce a brown ring at the junction of fluid if nitric acid is present. 

Medico Legal Importance 

• Accidental poisoning may arise from mistaken identity since sulfuric acid resembles glycerine and castor oil. It is therefore imperative that it is stored in a distinctive bottle, clearly labelled, and kept in a safe place.
• Sulfuric acid is a rare choice for either suicide or homicide.
• In addition to routine viscera and body fluids, a portion of corroded skin should be cut out, placed in rectified spirit or absolute alcohol and sent for chemical analysis.
• Vitriol: it is throwing off a corrosive substance over the face of an adversary due to revenge or jealousy. Sulfuric acid though is commonly used, any other corrosive acid is also used.

Conclusion 

Exposure to nitric acid can result in irritation to the eyes, skin, and mucous membranes. It can also cause delayed pulmonary edema, bronchitis, pneumonitis, and dental erosion. Nitric acid is highly corrosive and hazardous to both humans and animals.

Workers may be harmed from exposure to nitric acid and as nitric acid is an important industrial chemical for the manufacture of fertilizers and explosives.