Arsenic is one the oldest metal poison known to humans. It has been extensively used and misused throughout the ages to poison human being as well as animals. Arsenic is a metalloid i.e. it is an element which resembles a metal in some respects, and arsenic in the metal or metalloid form is not poisonous but its oxides are highly poisonous. It is a silver-grey or tin-white, shiny, brittle, crystalline and metallic-looking element. It is rarely found in its isolated, elemental form. Arsenious oxide or arsenic trioxide (sankhya or somalkhar) is the most common form of arsenic used, and is known as white arsenic or arsenic.
It occurs in two forms :
(a) white, smooth, heavy, crystalline powder,
(b) white and opaque solid mass similar to procelain.
It is white, tasteless and odourless and one of the strongest poisons. It can be administered in all types of food and drinks. The poison is more effective in solution form and dust form. The arsenic has inorganic and organic compounds.
Some Inorganic compounds of Arsenic are as follow:
- Arsenious oxide (Arsenic trioxide) – White crystalline powder
- Arsenic disulphide – Red powder
- Arsenic trisulphide – Yellow powder
- Arsenic trichloride – Colourless fuming liquid
- Arsine – Colourless and inflammable gas, Garlicky odour
- Sodium arsenates – White or grayish powder
- Sodium arsenite – White powder
- Potassium arsenite – White powder
- Copper arsenite – green Greenish crystalline powder
- Copper acetoarsenite – Greenish crystalline powder
Organic compounds of arsenic are as follow:
- Cacodylic acid
- Sodium cacodylate
100 to 500 mg
- 2-3 hours in acute cases.
- 12-24 hours in less acute cases.
- In some cases death occurs after number of days.
- Death may take months when the poison is administered in small doses.
- For homicidal purpose, Arsenic is mixed with food stuffs, cooked food, sweet meal, soft drinks, milk or drinking stuffs and medicine.
- It has been administered through tobacco and cigarettes.
- It has been administered through as holy water.
- It has been in enema fluid.
- It has also been injected into vagina for abortion.
Absorption, Excretion and Metabolism
► Arsenic is absorbed through all routes viz. through skin, inhalation, and GIT mucosa. However, cutaneous absorption is low except in cases of damaged skin. The inorganic pentavalent forms are absorbed at higher rate than bivalent forms.
► The absorbed inorganic arsenic undergoes methylation mainly in liver to monomethylarsonic acid and dimethylarsinic acid and excreted in urine.
► After absorption, arsenic is redistributed to the liver, lungs, intestinal wall, spleen, and kidneys. It has minimal penetration in blood-brain-barrier.
Mechanism of Action
Arsenic reversibly combines with sulphydrl enzymes. It blocks Krebs cycle and interrupts oxidative phosphorylation causing depletion of ATP and death of cell. It also inhibits transformation of thiamine into acetyl CoA and Succinyl –CoA leading to thiamine deficiency. It replaces the phosphorus within the bones. Arsenic is incorporated into hair, nails and skin. It causes increased permeability of small blood vessels with inflammation and necrosis of intestinal mucosa thus causing manifestation of hemorrhagic gastroenteritis.
Sign and Symptoms
The symptoms of acute poisoning occur within 30 minutes of the exposure. A patient with acute arsenic consumption may shows symptoms like-
- Circulatory failure
- Metallic taste in the mouth
- Slight garlic smell in breath
- Intense thirst
- Ventricular tachycardia
- Burning pain in throat and stomach
- Severe diarrhea
When a small quantity of arsenic is administered slowly at a repeated intervals to cause death, it is called a sub-acute poisoning. This results when arsenic is given in small doses at frequent intervals. The symptoms are-
- Tingling in throat followed by vomiting
- Diarrhea with tenesmus and abdominal pain
- Cramps in muscle
The features are exhibited in four stages-
- GIT symptoms dominate
- Loss of appetite
- Colicky abdominal pain
- Constipation (sometimes diarrhea)
- Circumscribed edema of ankle
- Periorbital edema
- Cutaneous eruptions
- Voice – hoarse and husky
- Skin – generalized or localized fine mottled pigmentation of skin.
- Epithelial hyperplasia with keratosis – mostly on sole and palm
- Nails become brittle and show Mees’ line
- Hairs become dry and may fall off
- Tingling and numbness of extremities
- Cramps in muscle and tenderness
- Knee jerk lost
- Peripheral neuropathy
- Neuropathy is hallmark of arsenic poisoning.
Forensic Examination and Test for Detection
Reinsch Test – It is good screening test. A copper wire, foil or strip is placed in a boiling dilute hydrochloric acid solution of the product. A greyish black deposit indicates arsenic. A greyish black copper foil is cut into small pieces, taken into Reinsch tube and heated over a low flame. Then, characteristics octahedral crystals of arsenic oxide are seen on the cold part of the tube under a microscope.
Marsh Test – It is very delicate test. The suspected substance containing arsenic-compounds is put in a vessel generating hydrogen gas (Woulffe’s bottle). The gas ‘arsin’ is formed. It burns will garlic smell and characteristics flame deposited a greyish residue.
Guitzeit Test – A silver nitrate paper turns yellow if it contact with vapours coming out of a heated mixture containing arsenic, zinc and sulphuric acid.
Bettendorffs Reaction – Oxidized viscera is heated with stannous chloride and strong hydrochloric acid in beaker. Then, blackish precipitate formed which indicates arsenic.
Spectrographic Analysis – Arsenic is also estimated and detected by spectrographic analysis.
- Vomitus and purges
- Blood and Urine
- Stomach contents
- Liver, Kidney, Spleen
- Burnt bones and ashes in case the victim has been cremated.
- Hairs, nails and skin (especially scrapping from the soles of the feet)- They are useful in slow poisoning, over a long period.
- Gastric lavage .
- Administer activated charcoal.
- Aggressive fluid resuscitation and cardiovascular support remains the mainstay of initial management.
- Chelation-This can be done with BAL (British Anti Lewisite or dimercaprol), penicillamine, DMSA (Dimercapto succinic acid), or DMPS (Dimercapto propane sulfonic acid). Every 50 mg BAL binds 30 mg of arsenic.
- Exchange transfusion.
- Continuous venovenous hemodiafiltration.
- Gastrointestinal congestion is a seen feature in acute arsenic poisoning. The mucosa may be reddened or show hemorrhagic gastroenteritis. The focal hemorrhages give rise to flea bitten appearance and this appearance is considered as characteristic. The mucosal appearance may be red velvet like.
- Subendocardial haemorrhages are often seen in the heart.
- There may be evidence of fatty degeneration of heart, liver, and kidneys.
- Chronic arsenic poisoning may present features of nonspecific gastrointestinal inflammation, as well as renal and hepatic damage, at autopsy.
- Due to dehydration, the body may show features like sunken eyeballs and it may appear to be shrunken.
- The petechial haemorrhages may be seen.
- Ulceration may be seen.
- Oedema may be seen in lungs.
- It is conventional to preserve apart from the routine viscera and body fluids, a piece of long bone (preferably femur), a bunch of pulled scalp hair, a wedge of muscle, and a small portion of skin (from the back of the trunk) for chemical analysis.
Medicolegal significance of Arsenic Poisoning
► Arsenic is widely used for homicidal purpose because it is cheap and easily available. For homicide, arsenic is administered orally mixed with some articles of food like sweets, bread, milk, tea, cold drinks, etc
► It is also used as cattle poison.
► Accidental poisoning is due to-
• Used in indigenous medicine (in case of chronic poisoning )
• Mistaken for medicine
• Arsenophagist – some people take arsenic daily as an aphrodisiac and are habituated for arsenic.
- Dr. K.S. Narayan Reddy. The essential of forensic medicine and toxicology.34th edition.
- VV Pillay.Modern medical toxicology.4th edition.