Physical properties: Thallium is a soft, heavy metal having a tin-white lustrous color which tarnishes on exposure to air owing to formation of thallous oxide.
Toxic Compounds and its Uses
- Thallium acetate: Colorless and almost tasteless. It was utilized in the past as a depilatory within the treatment of ringworm of scalp, for removing the superfluous hair, as constituent of some proprietary depilatory creams, in fireworks and as a rodenticide and insecticide.
- Thallium sulphate is used for killing rats and ants.
Mechanism of Action
The exact mechanism of toxicity is unknown but may involve disruption of sulphydryl groups on the mitochondrial membrane and interference with the function of sodium-potassium ATPase that thallium has 10 times more affinity than potassium.
In addition, it’s been suggested that thallium may interfere with riboflavin homeostasis resulting in dermatitis, alopecia and neuropathy. It has further been suggested that thallium is capable of breaking down all cells within the body, especially hair follicles and therefore the central nervous system.
Signs and Symptoms of thallium poisoning
In acute poisoning, signs and symptoms occur between one to 12 days.
System Signs and symptoms (Acute poisoning)
GIT: Irritation, metallic taste in mouth, nausea, vomiting, abdominal pain, anorexia, dryness of mouth, colic, diarrhea or constipation.
RS: Distress, running nose.
Ocular: Conjunctivitis, scotoma, blindness.
MS: Polyneuritis, tingling and pain sensation in hands and feet, muscular weakness with paralysis of some muscles, tremors.
CNS: Confusion, insomnia, psychosis, ataxia, organic brain syndrome, delirium, coma.
Others: Loss of hair of the scalp, eyebrows, body and axillary hair.
In mild cases, the symptoms are joint pains within the legs and feet, loss of appetite, stomatitis, drowsiness, and hypochlorhydria. These generally occur in few days.
In severe cases
• In sub-acute cases, Mees lines-there’s encephalopathy with white stripes across the nails.
(i )Beau lines—white lines across the nails due to trauma, skin condition, or hypercalcaemia
(ii )Muercke lines— white bands in the nail bed associated with hypo albuminaemia; and
(iii )Terry nails—white colouration of nails, apart from distal portion (which could also be pinkish), seen in cirrhosis.
• In chronic exposure, the symptoms appear in milder forms. The diagnosis could also be difficult because it’s often unsuspected.
– There could also be extreme sensitivity of the legs, followed by ‘burning feet’ syndrome and paresthesia.
• In fatal cases, death appears natural and is preceded by delirium, convulsions and coma.
Fatal dose
• Adults: 200 mg-1 g (> 8 mg/kg).
• Children: 8 mg/kg body wt.
Fatal period: death may occur in 24 to 36 hours.
Laboratory Investigations
• Eosinophilia is a common phenomenon.
• Thallium > 40 μg% in blood, and > 150 μg/l in urine is significant.
• Urine may be green.
Diagnosis
• GIT and polyneuritic symptoms together with the falling out of the hair of the head, eyebrows and axilla should cause suspicion of thallium poisoning.
• A brownish black pigmentation close to the hair root is characteristic of thallium exposure and should appear as early as 3rd-4th day.
• Opacity within the liver on X-rays has been reported.
Treatment
i. Patient should be kept warm.
ii. Vomiting is indicated within 4-6 h of ingestion.
iii. Multiple-dose activated carbon could also be given, followed by saline purgative. Whole bowel irrigation with polyethylene glycol electrolyte lavage solution could also be useful.
iv. Stomach wash is performed with 1% sodium or iodide solution. It forms iodide salts of thallium.
v. Prussian blue or Berlin blue (potassium ferric hexacyanoferrate) which acts to sequester the ions within the intestine and preventing their absorption is given during a dose of 250 mg/kg/day orally in two divided doses.
vi. Although chelating agents including BAL and EDTA are contraindicated within the treatment, sodiumdiethyl- dithio-carbamate 25 mg/kg body wt in 500 ml of 5% glucose given IV once daily could also be given.
vii. Pilocarpine in usual doses is additionally a physiological antidote.
viii. Potassium chloride promotes renal excretion of thallium. Administration of sodium polystyrene
sulphonate as sodium-thallium exchange resin could also be helpful.
ix. Hemodialysis/peritoneal dialysis may be useful within 48 h of ingestion.
x. Stimulants, dextrose and calcium salts are used according to necessity.
Postmortem Findings
i. There is anemia and loss of hair.
ii. Stomach: Mucosa could also be inflamed and there could also be submucous petechial hemorrhages.
iii. Spleen: Congested.
iv. Liver: Congested and shows fatty degeneration.
v. Kidneys: Congested, glomeruli are swollen, convoluted tubules show cloudy swelling and necrosis of the cells.
vi. Trachea and bronchi: Congested.
vii. Lungs: Congested with subpleural hemorrhages.
viii. Heart: Fatty degeneration.
ix. Brain: Meningeal vessels may be congested.
x. Cells of cortex, thyroid and hair follicles show degenerative changes.
Medico-legal Aspects
• Poisoning by thallium is rare in comparison to poisoning by lead or mercury, probably due to its infrequent use.
• Thallium was used as an ideal homicidal poisoning in some European countries and Australia, where it absolutely was used as rodenticide.
• Accidental intoxication may result from its therapeutic use as a depilatory.
• Chronic poisoning occurs from industrial.
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