Describe the poisoning by arsenic, lead and mercury.

Arsenic

• Arsenic has been called the "king OF poisons and the poison OF KINGS", and was the classical homicidal poison because it is tasteless, odourless, white and readily mistaken for sugar or flour, and because its symptoms closely mimic gastroenteritis and cholera. It is now largely displaced by other agents but remains important, and chronic environmental arsenicosis from contaminated groundwater is a major public health problem in West Bengal, Bihar and adjoining regions
• Sources — arsenic trioxide (white arsenic, sankhya); copper acetoarsenite (Paris green); pesticides and wood preservatives; ARSINE gas in metal refining, which causes massive haemolysis; and contaminated groundwater and traditional remedies

• Postmortem findings — the body is often well preserved, because arsenic retards putrefaction, which is a valuable pointer at exhumation; the gastric mucosa is congested, with a "red velvety" appearance and submucosal haemorrhages; there may be yellow arsenic sulphide particles adherent to it; and there is fatty change in the liver, kidney and heart
• Analysis — urine, blood, and above all hair and nails, in which arsenic is deposited as they grow and persists indefinitely. segmental analysis along the hair shaft gives a chronological record of exposure over months, distinguishing a single large dose from repeated small ones — which is decisive in chronic homicidal poisoning. The reinsch and MARSH tests are the classical methods, and atomic absorption spectrophotometry the modern one
• Note that arsenic occurs naturally in soil, so at exhumation control soil samples from above, below and beside the coffin are essential
• Treatment — supportive; gastric lavage; and chelation with BAL (dimercaprol), DMSA (succimer) or penicillamine

Lead

• Chronic lead poisoning (plumbism, saturnism) is far commoner than acute, and is essentially an occupational and environmental disease
• Sources in India — battery manufacture and recycling; paints and pigments; printing; welding and smelting; lead pipes; traditional and ayurvedic remedies, and surma or kohl applied to infants’ eyes, which are a recognised and continuing cause of childhood poisoning; contaminated spices; and formerly leaded petrol
• Clinical features — the classical picture: facial pallor, an early and characteristic sign; a burtonian line, a blue-black line of lead sulphide along the gum margin adjacent to carious teeth; colicky abdominal pain (lead or "painter’s" colic) with obstinate constipation; anaemia with basophilic stippling of the red cells and raised free erythrocyte protoporphyrin; wrist drop and foot drop from a motor neuropathy affecting the extensors; lead encephalopathy, particularly in children, with convulsions, raised intracranial pressure and coma; and nephropathy with gout ("saturnine gout")
• In children the effects are on the developing brain, producing irreversible cognitive impairment and behavioural disturbance at blood levels well below those causing symptoms in adults; there is no established safe level
• Radiologically — dense "lead lines" at the metaphyses of the growing long bones in children, and radio-opaque material in the gut if recently ingested
• Treatment — removal from exposure, which is the essential step; and chelation with calcium disodium EDTA, BAL and DMSA

Mercury

• Three quite different clinical pictures, according to the form:
• Elemental mercury vapour — inhaled; causes pneumonitis acutely, and chronically the classical triad of tremor, erethism and gingivitis. erethism is a striking personality change with shyness, irritability, loss of confidence, memory impairment and depression — the "mad hatter" syndrome, from the use of mercuric nitrate in hat-making. Swallowed metallic mercury is almost harmless, being poorly absorbed
• Inorganic salts — mercuric chloride (corrosive sublimate) — a violent corrosive and irritant: burning pain, a metallic taste, greyish burns of the mouth, vomiting, bloody diarrhoea, and acute tubular necrosis with anuria, which is the usual cause of death. Chronic exposure gives stomatitis with a blue line on the gums, salivation, loosening of the teeth and a metallic taste
• Organic — methylmercury — the most dangerous form; lipid-soluble, crosses the blood-brain barrier and the placenta, and is bioaccumulated in fish. Causes minamata disease: constriction of the visual fields, ataxia, dysarthria, deafness and paraesthesiae; and in the fetus, severe cerebral palsy and intellectual disability in a mother who is herself unaffected
• Acrodynia (pink disease) — in children exposed to mercury in teething powders: painful pink swollen hands and feet, photophobia, irritability and desquamation
• Treatment — chelation with BAL, DMSA or penicillamine; and note that BAL is contraindicated in methylmercury and in organic lead, since it redistributes the metal to the brain and worsens the neurological injury

Applied Aspects

• Suspect arsenic where an illness resembling cholera recurs at home and remits in hospital, especially with a neuropathy and skin changes; and take hair and nails for segmental analysis
• Take control soil samples at any exhumation for arsenic; the element occurs naturally in soil and its presence in the body is otherwise arguable
• Ask about surma, kohl and traditional remedies in any child with unexplained anaemia, abdominal pain or developmental regression; they remain a live cause of lead poisoning in India
• Look for basophilic stippling and a Burtonian line, and radiograph the long bones in a child; the diagnosis is easily made and easily missed
• Remove from exposure before chelating; chelation without removal simply mobilises the metal and the exposure continues
• Do not give BAL in methylmercury or organic lead; it redistributes the metal into the brain and makes the neurological outcome worse
• Swallowed metallic mercury from a thermometer is essentially harmless, and reassurance is the correct treatment; inhaled vapour from a spill is not, and the area must be ventilated and cleaned properly
• Arsenic retards putrefaction, so an unexpectedly well-preserved body at exhumation is itself a pointer
• Mees lines date the exposure as they grow out with the nail, and segmental hair analysis reconstructs the pattern of dosing
• Swallowed metallic mercury is nearly harmless, while its vapour is not; the form determines everything in mercury poisoning
• Erethism is the personality change of mercury — shyness, irritability and loss of confidence — and precedes the tremor
• Methylmercury crosses the placenta, so a severely affected infant may be born to an unaffected mother, as at Minamata
• Lead affects children at levels harmless to adults, and the cognitive damage is irreversible, so there is no safe threshold
• Arsenic mimics cholera with rice-watery stools, and that resemblance is what allowed so many homicidal poisonings to pass as disease
• Groundwater arsenicosis affects millions in West Bengal and Bihar, and is a public health problem rather than a forensic one
• Wrist drop and foot drop in lead come from a motor neuropathy affecting the extensors, and are a late sign
• Basophilic stippling occurs in both lead and arsenic, and is a simple finding on a routine blood film
• Lead lines at the metaphyses are visible on a plain radiograph of a child long bone and confirm chronic exposure
• Mercuric chloride kills by acute tubular necrosis, and the corrosive gastrointestinal phase precedes the renal failure
• Acrodynia followed mercury in teething powders, with painful pink swollen hands and feet in an irritable photophobic child
• Take control soil at every exhumation for arsenic; the element occurs naturally and its presence is otherwise arguable
• Surma and kohl remain a live cause of childhood lead poisoning in India, and must be asked about directly
• Remove from exposure before chelating; chelation while exposure continues achieves nothing durable
• Do not give BAL in methylmercury or organic lead; it redistributes the metal to the brain and worsens the outcome
• Saturnine gout follows lead nephropathy, and is a useful pointer in an adult with unexplained joint pain and renal impairment
• Arsine gas causes massive haemolysis rather than the gastrointestinal picture, and arises in metal refining
• The mad hatter syndrome came from mercuric nitrate used in hat-making, and erethism remains the name for that personality change