Lead Poisoning - Park's Textbook of Preventive and Social Medicine (p. 910-911)

Introduction

1. Low boiling point
2. Mixes easily with other metals to form alloys
3. Easily oxidised
4. Anticorrosive

Sources of Exposure

Industrial Uses

• Manufacture of storage batteries
• Glass manufacture
• Ship building
• Printing and potteries
• Rubber industry and several others

Non-Occupational Sources

• Gasoline - the greatest source of environmental (non-occupational) lead; thousands of tons of lead are exhausted from automobiles every year
• Drinking water from lead pipes
• Children chewing lead paint on window sills or toys

Mode of Absorption

1. Inhalation - Most cases of industrial lead poisoning result from inhalation of fumes and dust of lead or its compounds
2. Ingestion - Less common. Small quantities trapped in the upper respiratory tract may be swallowed. Lead may also be ingested via contaminated hands, food, or drink
3. Skin - Absorption occurs only with organic compounds of lead, especially tetraethyl lead. Inorganic compounds are NOT absorbed through the skin

Body Stores and Distribution

• Normal body store: 150 to 400 mg in the average adult
• Normal blood level: ~25 μg/100 ml
• Clinical symptoms appear at: ≥70 μg/100 ml blood lead level
• Normal daily intake: 0.2 to 0.3 mg/day (from food and beverages)

• 90% of ingested lead is excreted in the faeces
• Absorbed lead enters circulation → 95% enters erythrocytes → transported to liver and kidneys → finally deposited in bones
• Bone lead is "metabolically inactive" but may be released to soft tissues during bone resorption

Clinical Picture (Plumbism)

Inorganic Lead Poisoning

• Abdominal colic
• Obstinate constipation
• Loss of appetite
• Blue line on the gums (Burton's line)
• Stippling of red cells (basophilic stippling)
• Anaemia
• Wrist drop and foot drop (peripheral neuropathy)

Organic Lead Compounds (e.g., tetraethyl lead)

• Insomnia
• Headache
• Mental confusion
• Delirium

Diagnosis

Preventive Measures

1. Substitution - Replace lead compounds with less toxic materials where possible
2. Isolation - Enclose and segregate processes generating harmful lead dust or fumes
3. Local exhaust ventilation - Adequate ventilation to remove fumes and dust promptly
4. Personal protection - Approved respirators for workers
5. Good housekeeping - Wet sweeping of floors, benches, and machines to control dust
6. Working atmosphere - Lead concentration in workplace air must be kept below 2.0 mg per 10 cubic metres (permissible limit/threshold value)
7. Periodic examination of workers - Regular medical examination including urinary lead, blood lead, RBC count, haemoglobin, CPU test, and basophilic stippling estimation. WHO Expert Committee stresses that blood lead must not exceed 70 μg/ml and ALA in urine must not exceed 10 mg/litre
8. Personal hygiene - Hand-washing before eating; no food in work areas; adequate washing facilities
9. Health education - Educate workers on risks and personal protection

Management

1. Prevention of further absorption
2. Removal of lead from soft tissues
3. Prevention of recurrence

• Early recognition and removal from further exposure
• Saline purge to remove unabsorbed lead from the gut
• D-penicillamine - chelating agent; promotes lead excretion in urine (similar to Ca-EDTA)
• Ca-EDTA - chelating agent for lead excretion in urine

Important note: Lead poisoning is a notifiable and compensatable disease in India since 1924.

Lead Poisoning - Outline

I. CAUSES (Sources & Mode of Absorption)

A. Sources of Lead

• Lead is used in over 200 industries
• Storage battery manufacture
• Glass manufacture, ship building
• Printing and potteries
• Rubber industry

• Gasoline/automobile exhaust - greatest non-occupational source
• Drinking water through lead pipes
• Children chewing lead paint on toys or window sills
• Contaminated food and beverages (0.2-0.3 mg/day normally ingested)

B. Mode of Absorption

C. Mechanism of Toxicity

• Lead combines with SH-groups of enzymes involved in porphyrin synthesis and carbohydrate metabolism
• Affects membrane permeability - causes potassium leakage from erythrocytes
• 95% of absorbed lead enters erythrocytes → liver → kidneys → deposited in bones

II. CLINICAL FEATURES (Plumbism)

A. Inorganic Lead Poisoning

• Abdominal colic
• Obstinate constipation
• Loss of appetite
• Abdominal cramps

• Blue line on gums (Burton's line) - pathognomonic

• Anaemia
• Basophilic stippling of RBCs

• Wrist drop (extensor paralysis)
• Foot drop
• Joint and muscular pains
• Weakness, persistent headache

B. Organic Lead Poisoning (e.g., tetraethyl lead)

• Insomnia
• Headache
• Mental confusion
• Delirium

C. Key Blood Level Thresholds

III. MANAGEMENT

Objectives

1. Prevention of further absorption
2. Removal of lead from soft tissues
3. Prevention of recurrence

Steps

1. Remove from exposure - Early recognition and removal of the worker from further lead exposure
2. Saline purge - To remove unabsorbed lead from the gut
3. Chelation therapy:
   • D-penicillamine - chelating agent; promotes lead excretion in urine
   • Ca-EDTA - chelating agent; same mechanism (promotes urinary excretion of lead)

Lead poisoning is a notifiable and compensatable disease in India since 1924.

IV. PREVENTION

A. Engineering Controls

1. Substitution - Replace lead compounds with less toxic alternatives where possible
2. Isolation/Enclosure - Enclose and segregate all processes generating lead dust or fumes
3. Local exhaust ventilation - Adequate ventilation to promptly remove fumes and dust
4. Atmospheric monitoring - Lead in workplace air must remain below 2.0 mg per 10 cubic metres (permissible limit)

B. Personal Protection

1. Approved respirators for all exposed workers
2. Personal hygiene - Handwashing before eating; prohibit eating in work areas; adequate washing facilities

C. Medical Surveillance

1. Periodic examination of workers:
   • Urinary lead (normal: 0.2-0.8 mg/litre; >0.8 mg/litre indicates exposure)
   • Blood lead (should not exceed 70 μg/ml)
   • ALA in urine (should not exceed 10 mg/litre per WHO; >5 mg/litre indicates absorption)
   • Coproporphyrin in urine - CPU (screening test; normal <150 μg/litre)
   • RBC count, haemoglobin, basophilic stippling

D. Administrative Measures

1. Good housekeeping - Wet sweeping of floors, benches, and machines
2. Health education - Educate workers on risks and personal protection measures