Heavy Metals: Exposure, Assessment and Clinical Caution

Heavy metals occupy an odd position in healthcare. Genuine metal poisoning, particularly lead, remains a significant global problem that is often missed. At the same time, heavy metal toxicity has become a popular explanation for vague symptoms, diagnosed with unvalidated tests and treated with chelation therapy that carries real risks. Practitioners need to recognise genuine exposure, test for it correctly and avoid contributing to harmful practices.

Lead

Why it matters

Lead has no biological function, and there is no known safe level of exposure. In children, even low blood lead levels are associated with reduced IQ, attention problems and behavioural difficulties. In adults, lead raises blood pressure and is associated with cardiovascular disease, kidney impairment and cognitive effects. During pregnancy, lead stored in bone is mobilised and crosses the placenta.

Sources

• deteriorating lead paint and dust in older housing, particularly during renovation;
• old lead water pipes;
• contaminated soil near roads, industry or former mining;
• occupations such as battery recycling, construction, smelting and firearms instruction;
• some imported spices, ceramics and cookware;
• some traditional remedies, including certain Ayurvedic and other traditional preparations, and cosmetics such as some kohl and sindoor products.

Assessment

Blood lead level is the standard test and reflects recent and ongoing exposure. Public health bodies use reference values, such as the blood lead reference value in the United States, to identify children with higher exposure than most. Management depends on the level and focuses on identifying and removing the source, nutritional support with adequate iron and calcium, and chelation only at high levels under specialist care.

Mercury

Mercury exists in different forms with different sources and toxicity.

Pregnant women and young children are advised to choose lower mercury fish rather than avoid fish, because fish provides important nutrients. Dental amalgam releases small amounts of mercury vapour; regulators have concluded that it is not harmful for most people, while suggesting alternatives for some higher risk groups where appropriate. Removing intact amalgam fillings is not recommended solely to reduce mercury exposure, as removal itself releases mercury vapour.

Arsenic

Inorganic arsenic, mainly from contaminated groundwater, causes skin lesions, cancers of the skin, bladder and lung, cardiovascular disease and diabetes. It is a major public health problem in parts of South Asia, South America and elsewhere. Rice absorbs more arsenic than other grains, and rice based foods can contribute to intake. Seafood contains large amounts of organic arsenic compounds, such as arsenobetaine, which are relatively non toxic. Urine arsenic testing should therefore be speciated to distinguish toxic inorganic arsenic from harmless seafood arsenic, and recent seafood intake should be avoided before testing.

Cadmium

Cadmium accumulates in the kidneys and bones over decades. Major sources are tobacco smoke and some foods, particularly from contaminated soils, as well as occupational exposure. Chronic exposure causes kidney damage and bone loss and is associated with some cancers. Urine cadmium reflects long term body burden.

Aluminium

Aluminium toxicity occurs mainly in people with kidney failure, historically causing dialysis related encephalopathy and bone disease. The hypothesis that aluminium causes Alzheimer disease in the general population has not been supported by the weight of evidence.

Tests to avoid

Hair analysis

Hair analysis for metals is marketed widely. A study that sent identical hair samples to several commercial laboratories found highly inconsistent results and recommendations between laboratories. Hair is affected by external contamination, hair treatments and washing, and reference ranges are not standardised. Hair testing has specific uses in forensic and research settings but is not reliable for diagnosing metal toxicity in individuals.

Provoked urine testing

Some practitioners give a chelating agent and then measure metals in urine, comparing results with reference ranges for unprovoked samples. Chelating agents increase urinary excretion of metals in everyone, so provoked results will appear elevated even in people with normal exposure. Toxicology organisations have advised against this practice because it lacks validated reference values and leads to misdiagnosis.

Chelation therapy

Chelation therapy uses drugs that bind metals so they can be excreted. It is appropriate for significant lead poisoning, some other metal poisonings and iron overload, under specialist care. Used outside these indications, it carries serious risks, including dangerous drops in calcium, kidney injury and deaths, which have been reported with inappropriate use of some chelating agents. A trial of chelation in people after heart attack reported a modest benefit, particularly in people with diabetes, but a subsequent trial did not confirm benefit, and chelation is not recommended for cardiovascular prevention.

A practical approach

1. Take an exposure history: housing, water, occupation, hobbies, diet, fish intake, traditional remedies, cosmetics, country of origin.
2. Test when history or clinical features suggest exposure, using validated tests appropriate to the metal and form.
3. Interpret with reference values from appropriate populations and laboratories.
4. Identify and remove the source, which is the most important intervention.
5. Support nutrition, particularly iron and calcium in lead exposure.
6. Refer to toxicology or occupational medicine for significant exposures.
7. Avoid hair analysis, provoked testing and chelation outside established indications.

An illustrative case

A 45 year old woman originally from South Asia presents with fatigue, abdominal pain and anaemia. She has been taking a traditional preparation for joint pain sent by relatives for 2 years and applies a traditional powder to her hair parting. Her blood lead is significantly raised. Both products are stopped and sent for analysis, and she is referred to a toxicology service, which decides on management based on her level. Her family members are tested. Her anaemia is treated. Her joint pain is reassessed and managed with physiotherapy. A careful history and a single validated test identified genuine poisoning.

Real toxicity, real tests

Heavy metal toxicity is real and preventable, and practitioners who take good exposure histories can find it. Using validated tests and reserving chelation for genuine indications protects patients both from the metals themselves and from the harms of misdiagnosis.