HEAVY METALS AND THEIR HEALTH IMPACTS

Heavy metals are metals with high densities, atomic weights, and atomic numbers. Some are essential nutrients (iron, cobalt, zinc), but toxic in excess. Others (lead, cadmium, mercury, chromium, arsenic) are highly poisonous even in small quantities.

LEAD
- Most common cause of heavy metal poisoning.
- Major source earlier was leaded petrol (phased out in India in 2000).
- Still used in neighbouring countries like Afghanistan, Myanmar, Iran.
- Causes: Brain and nervous system damage, kidney damage, interference with RBC formation.

CADMIUM
- Sources: Industrial waste, batteries.
- Causes: Heart damage, cancers, skeletal, urinary, reproductive, and cardiovascular toxicity.
- Long exposure leads to slow muscular and neurological degeneration.

PERMANENT ENVIRONMENTAL IMPACT
- Heavy metals cannot be degraded once released.
- Long‑term contamination of soil, water, and food chain.

SOURCES OF HEAVY METAL POISONING
- Mining (chromium, cadmium, lead, mercury)
- Industrial waste, tailings
- Agricultural runoff
- Occupational exposure
- Paints
- Treated timber

HEAVY METALS IN INDIAN RIVERS (CENTRAL WATER COMMISSION STUDY)
- 65% of samples polluted.
- Iron most common contaminant (156/442 sites above safe limit)
- Other contaminants: Lead, nickel, chromium, cadmium, copper
- Arsenic not above safe limit at any site.
- Delhi‑NCR: ~41% population shows heavy metal toxicity (2019 study)
- AIIMS found excess iron, mercury, lead in patients.
- NEERI study: Dangerous metal levels in vegetables along Yamuna.

LEAD POISONING
- No safe level of lead in blood.
- 5 mcg/dL affects mental development; >100 mcg/dL fatal.

Uses:
- 75% of global consumption in lead‑acid batteries.
- Also in paints, pigments, ceramics, solder, toys, cosmetics.

Exposure Routes:
- Inhalation during smelting, recycling
- Ingestion of contaminated soil, dust, water (leaded pipes), food (lead‑soldered containers)
- Some traditional medicines (India, Mexico, Vietnam)

Health Impacts:
- Children extremely vulnerable
- Causes: Brain damage, developmental delays, anaemia, hypertension, kidney damage
- Pregnant women: Miscarriage, premature birth, low birth weight

UNEP — WORLD FREED FROM LEADED PETROL
- Global elimination achieved recently.
- India phased out leaded petrol in 2000.
- Benefits estimated at $2.44 trillion annually globally.

MERCURY POLLUTION
Sources:
- Natural: Earth’s crust, volcanoes, oceans
- Human: Coal combustion, gold mining, hazardous waste burning, chlorine production, broken mercury products
- Improper disposal (e.g., Kodaikanal Hindustan Lever incident)

Exposure:
- Majority from eating methylmercury‑contaminated fish and shellfish
- Vapour inhalation in closed spaces

Health Impacts:
- Neurotoxin: damages CNS, affects brain development in infants
- Impairs immunity, motor functions
- Wildlife effects: Poor fish schooling, fewer bird eggs, impaired hunting in mammals

Standards:
- Drinking water: 0.001 mg/L (India, WHO)
- Industrial waste: 0.01 mg/L

Mercury in India:
- High levels found in rivers near industrial units
- Severely affected: Mumbai, Kolkata, Karwar, North Koel
- Koel river: 600–700 times above permissible limits

MINAMATA CONVENTION ON MERCURY
- Global treaty to control mercury emissions.
- Goals: Ban new mercury mines, regulate air emissions, phase out mercury devices (thermometers, switches), regulate gold mining, ensure safe storage and disposal.
- India ratified in 2018 (5-year window for new plants, 10-year window for existing plants)

ARSENIC POLLUTION
- Tasteless, odourless metalloid.
- Major threat in groundwater across India.

Standards:
- BIS limit: 0.01 mg/L

Affected Areas:
- Most severe: Gangetic belt — UP, Bihar, Jharkhand, West Bengal, Assam
- Others: Punjab, Haryana, Manipur, Chhattisgarh, Karnataka

Sources:
- Natural leaching of rocks into aquifers
- Human: Coal plants, burning vegetation, volcanism
- Groundwater‑based irrigation aggravates contamination
- Enters food chain: rice husk used as livestock feed

Health Impacts:
- Long‑term exposure causes arsenicosis
- Leads to cancers: skin, bladder, kidney, lung
- Causes skin lesions, peripheral vascular disease, black‑foot disease
 

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Subject: Environment

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