Lead poisoning

What is lead poisoning?

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The biological effects of lead are dependent on the level and duration of exposure. Lead inhibits 3 enzymes of haem biosynthesis (δ amino levulinic acid dehydratase (ALAD), coproporphyrin oxidase, and ferrochelatase). This effects erythrocyte formation by impairing haem synthesis and also depresses the serum level of erythropoietin. Lead exposure also affects calcium metabolism.

Lead poisoning can cause nervous system toxicity and renal tubular dysfunction leading to irreversible interstitial nephrosis with progressive renal impairment and hypertension. The effect of long-term elevated lead levels on children is of particular concern and can lead to a reduction of IQ and to disruptive behaviour. Lead also depresses haem synthesis and shortens the lifespan of erythrocytes, causing a hypochromic microcytic anaemia. One study showed altered hippocampal volume and brain metabolites in workers occupationally exposed to lead.³

Another showed a significant increase in the frequency of chromosomal aberrations in workers exposed to lead compared to the controls.⁴ Steroid production is also impaired.

Acute lead poisoning is mainly related to occupational inhalation and foreign body ingestion. Chronic lead poisoning may be either environmental or occupational.

Lead poisoning incidence

Lead poisoning is a lot less common than it used to be, due to less use in petrol, paints or cosmetics, and generally improved housing.

Blood lead levels of less than 5 µg per dL are associated with impairments in neurocognitive and behavioral development that are irreversible.⁵Younger children are particularly at risk because of ingestion of foreign material, increased gastrointestinal (GI) absorption, and because their nervous systems are still developing.⁶⁷

In adults, lead poisoning is mostly occupation-related. The occupations mainly involved are the smelting, refining, alloying, and casting industry (19.1%), the lead battery industry (18.2%) and the scrap industry (7.4%).⁸

Risk factors for lead poisoning ²⁹

• Occupations involving contact with lead-containing products are radiation shields, ammunition, certain surgical equipment, developing dental X-ray films prior to digital X-rays, fetal monitors, plumbing, circuit boards, jet engines, and ceramic glazes. The risk of toxicity increases with increasing exposure. Those who work in metal welding, battery production or recycling and the building or breaking down of ships may also be at risk.

• Children chewing lead-painted items or ingesting fishing weights, bullets or contaminated soil.

• Deliberate ingestion (pica) is occasionally seen in adults as part of a psychiatric condition. ¹⁰

• Use of various imported tonics, alternative medication and cosmetics containing lead.

• Those with a deficiency of iron, calcium or zinc will absorb more lead from the GI tract, increasing their risk.

• Older houses (lead-based paint or pipes)

Acute lead poisoning symptoms

The severity of lead poisoning symptoms often correlates with blood levels - may patients are asymptomatic. At high levels the following may be seen:

• Abdominal pain - moderate-to-severe, usually diffuse but may be colicky and associated with constipation.

• Vomiting.

• Jaundice (due to hepatitis).

• Lethargy (due to haemolytic anaemia).

• Black diarrhoea.

Chronic lead poisoning symptoms

• Mild abdominal pain.

• Constipation.

• Reduced appetite and weight loss.

• Aggression.

• Antisocial behaviour.

• Headaches.

• Hearing loss.

• Subfertility.

• Peripheral neuropathy (eg, foot and wrist drop) and carpal tunnel syndrome.

• Gout and arthritis.

• Autonomic dysfunction.

• Encephalopathy - more common in children, characterised initially by irritability and tantrums and later by seizures, mania, delirium and coma, death.

Signs of lead poisoning

There are no pathognomonic signs of lead poisoning but the following may be seen:

• A blue discoloration of gum margins.

• Mild anaemia.

• Behavioural abnormalities (more marked in children) - irritability, restlessness, sleeplessness.

• Cognitive dysfunction.

• Impaired fine-motor co-ordination or subtle visual-spatial impairment.

• Chronic distal motor neuropathy with decreased reflexes and weakness of extensor muscles in adults.

This depends on the presentation. Lead poisoning diagnosis may be difficult in the UK where lead poisoning is a relative rarity but the condition should be on the list in patients presenting with diffuse abdominal pain.

Other conditions which may need to be considered include:

• Acute confusional states.

• Acute memory loss.

• Epilepsy.

• Encephalopathies.

• Frontal lobe syndromes.

• Depression.

• Attention deficit hyperactivity disorder.

• General learning disability (includes learning disorder, developmental delay, language disorder).

• Autism or pervasive developmental disorder.

• Organic solvent poisoning.

• Other heavy metal poisoning.

• Radial mononeuropathy and other peripheral neuropathies.

• Diabetic neuropathy.

• Anaemias, acute and chronic.

• Constipation.

• Guillain-Barré syndrome.

Laboratory tests

• Whole blood lead levels:

  • <10 μg/dL - normal in adults - associated with adverse effects on cognition and behaviour in children. ¹⁴

  • >45 μg/dL - GI symptoms in adults and children.

  • >70 μg/dL - high risk of acute CNS symptoms.

  • >100 μg/dL - may be life-threatening.

• The UKHSA in England and equivalent agencies in Wales and Scotland will get involved in source reduction and mitigation at a level of ≥5 μg/dL in children aged under 16, with legislation in Northern Ireland specifying action at the higher levels of 30 μg/dL for women of reproductive age, 50 μg/dL for those aged under 18 and 60 μg/dL for any other employee.^{1315 16}

• FBC - basophilic stippling of erythrocytes may be seen and features of a microcytic hypochromic anaemia such as a low MCV may be present. Sideroblasts may be seen.

• Renal function tests to detect renal complications and uric acid levels to detect gout may also be advisable.

• Nerve conduction tests should be considered if neuropathy is suspected.

• Psychometric testing should be considered if clinically indicated.

Radio-imaging¹⁷

• Plain X-ray may show transverse lines in tubular bones. These are actually areas of arrested bone growth and may persist for a long time after exposure ends. They are not seen in the early phase of exposure.

• Plain abdominal X-rays may show radio-opaque flecks in cases of suspected lead foreign body ingestion (for example, pica in children).

• X-ray fluorescence works by detecting specific emissions from tissues when bombarded with X-rays. It is a sensitive method of detecting low levels of lead in the body.¹⁸

• CT or MRI scan of the brain may be contributory in patients with symptoms suggestive of encephalopathy.

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Acute lead poisoning can affect all of the body systems and risks hepatic, renal, and neurological damage. The decision to use chelation therapy needs careful consideration as it can in itself lead to complications such as hypertension, acute kidney injury, and raised intracranial pressure.

Acute management is done in hospital and may require attention to the airway, IV fluids and in some cases chelation therapy or the removal of a lead containing foreign body by gastroscopy or colonoscopy. Complications of lead poisoning.

• Lead exposure is estimated to account for 143,000 deaths per year, with the highest burden in developing regions.

• Asymptomatic children with blood levels below 20 μg/dL require long-term neurodevelopmental follow-up, and counselling is required. In all cases, immediate removal of the source of lead exposure is essential .

• Cases of acute lead encephalopathy in children still occur and can result in severe neurological damage, seizure disorders, depressed school function, and learning disabilities.

• It is now acknowledged that, due to its cumulative effects, there is no known level of lead exposure that is considered safe.

• Adults tend to fare better but long-term effects can include distal motor neuropathies, depressive disorders, aggressive behaviour, defects in sexual performance and fertility problems.

• Evidence suggests that childhood lead exposure may raise the risk of adult neurodegenerative disease, particularly dementia.²¹

• The removal of paint from lead and the replacement of old lead pipes have done much to reduce the burden of lead poisoning, particularly on children. The aim has been to reduce lead levels in children to less than 10 μg/dL.

• It is now well established that neurotoxicity can develop below the level of 10 μg/dL and the Global Alliance to Eliminate Lead Paint has been formed by the World Health Organization and other bodies to minimise this risk.

• If appropriate, the family or co-workers of the patient should be screened.

• The Control of Lead at Work (CLAW) Regulations, 2002, require all employers to minimise the exposure of their employees to lead and to take measures to reduce such exposure (for example, encouraging personal hygiene, regular monitoring, suspension of employees with raised blood levels, training, and education).²³

• Global reduction in the use of lead-containing petrol has resulted in a significant reduction in exposure. However, new sources continue to emerge, including improper disposal of electronics and children's toys contaminated with lead.²⁴²⁵

• The lead content of some traditional health remedies is still a concern; education is needed.²⁶

• Further work needs to be done to reduce occupational exposure, particularly where industrial processes create lead dust, fume or vapour. Examples include blast removal, demolition, recycling of batteries, TVs or computer monitors, and working with lead or leaded-glass.²⁷²⁸