Medicosnext
Dr. Arun Dhungana
He is currently an Associate Professor, consultant biochemist and researcher at Kathmandu Medical College Teaching Hospital (KMCTH). He has been involved in teaching undergraduate medical, dental and allied health students, with focus on medical biochemistry, metabolism, molecular biology and laboratory medicine. His academic interests include biochemical and tumor markers, metabolic and endocrine disorders. He has contributed to research activity, curriculum development and student mentorship, encouraging the integration of basic biochemical concepts with clinical practice.
Just imagine being exposed to a toxin today that could remain in the body for decades. Unlike many chemical that are broken down and eliminated, certain toxic heavy metal (e.g., lead, mercury, cadmium and arsenic) persist in the environment and do not disappear naturally like other pollutants. Exposure of humans to these heavy metals silently influences the health and increase the risk of chronic disease.
That’s why heavy metal are often called the “silent pollutants,” since they rarely show any immediate effect and as a result they accumulate gradually, causing damage which become apparent often after decades.
Heavy metals are naturally occurring metallic elements that have a relatively high density, atomic weight or atomic number. These elements are categorized into several groups including alkali metals, transition metals, metalloids, reactive nonmetals and noble gases. Metals such as iron, zinc and copper are essential for normal biological functions, while other become toxic when present in excessive amounts. The most toxic heavy metal include lead (Pb), mercury (Hg), cadmium (Cd), arsenic (As), chromium (Cr), and nickel (Ni).
Through food, water, air, or occupational exposure these metals gradually build up in the body’s soft tissues and bone over long period or even decades. This phenomenon is known as bioaccumulation; a gradual build-up of substances, such as pesticides or heavy metal inside a living organism over time. It occurs when an organism absorbs a chemical faster than it can break it down or excrete. Once the heavy metals are released, they do not degrade and can persist in soil, water and food chain for generations.
How do these metals enter the body?
Exposure to this heavy metal primarily occurs through four routes:
- Consumption of contaminated food and water
- Inhalation of polluted air, dust or industrial fumes
- Occupational exposure in factories, mines and laboratories
- Skin contact with contaminated material
These metals are not easily metabolized and get stored in tissues rather than eliminating them completely.
“The toxins that never leave”
Heavy metals have long biological half-lives. Lead get stored in bones for more than two decades, cadmium accumulates in the kidney for 10-30 years. Mercury, particularly methylmercury, gets deposited in the brain and exerts long-term neurological effects. A repeated low level of exposure every day, gradually build a toxic burden which eventually overcome its protective mechanism.
Mechanism of toxicity
Oxidative stress
Heavy metals exert toxic effects on the human body which induce the formation of free radicals, leading to oxidative stress that damages essential cellular components including proteins, lipids, and nucleic acids. As a consequence, protein damage results in enzyme inactivation, protein misfolding, and aggregation, causing loss of normal cellular function, while lipid peroxidation results in damage to cell membranes, compromising cell integrity and survival.
DNA damage
They also interferes with DNA repair mechanisms and inactivates regulatory molecules and transcription factors, preventing the correction of genetic damage and disrupting normal gene expression. These alterations promote DNA damage accumulation and increase the risk of carcinogenesis (cancer development).
CNS Toxicity
Heavy metals directly affect the nervous system by inhibiting neurotransmitter function and damaging neurons, leading to neurotoxicity and neurological disorders.
Enzyme inhibition
They bind to enzymes and interfere with normal biochemical reaction, disrupting metabolism and cellular function.
Health consequences
These heavy metal toxic effects may vary depending on the type of metal, dose, duration of exposure, and individual susceptibility. It affects the various organs like brain and nervous system causing memory impairment, learning difficulties, developmental delays in children, tremors and neuropathy. The kidneys are the major targets of cadmium, mercury, and lead toxicity. Chronic exposure results in kidney dysfunction and failure. The accumulation of cadmium in bones contributes to bone demineralization and osteoporosis, increasing fracture risk. The chronic heavy metal exposures are linked with hypertension, atherosclerosis, and increased cardiovascular risk, while arsenic, cadmium, chromium, and nickel compounds are recognized as carcinogens.
Who are at more risk?
Children and infants, pregnant women, industrial and agricultural workers, smokers, populations dependent on contaminated groundwater and individuals living near industrial zones are the vulnerable groups
Can heavy metals be removed?
It requires identification and elimination of the source of exposure. Laboratory tests of blood, urine, hair, or tissues help assess the exposure levels.
In severe cases, use of chelation therapy, where administrations of agents that bind certain metals are used which facilitate their excretion. However, this might not be appropriate in all types of toxicity and cannot always reverse existing tissue damage. So, preventive measures are more effective than treatment.
Prevention: the best defense
Reducing exposure to heavy metal toxicity is one of the best initial steps for prevention. Small steps can provide significant protection. Therefore, using safe drinking water, avoiding lead based paints and household products, properly disposing of batteries and electronic waste, and maintaining good household hygiene can drastically minimize the risk. Practicing healthy dietary habits and consumption of balanced diet rich in calcium, iron, zinc, and vitamin C also help reduce the absorption of certain heavy metals in the body.
Workers must use appropriate personal protective equipment (PPE), follow workplace safety regulation and participate in health monitoring programs to detect exposure early. At the community level, stronger environmental regulations, continuous monitoring of industrial emissions, improved waste management practices, and public awareness campaigns are essential to reducing environmental contamination and protecting public health.
Conclusion
Heavy metals are the most persistent environmental pollutants that remain in the body and environment for years, quietly contributing to disease and disability. Through awareness, environmental responsibility, workplace safety, and informed lifestyle choices, individuals and communities can reduce exposure and protect future generations.
