Heavy Metals

Introduction

Heavy metals are among the most dangerous environmental pollutants because they:
➡️Persist in the environment
➡️Do not biologically degrade
➡️Accumulate in living organisms
➡️Move up the food chain (biomagnification)

Even at very low concentrations, they can cause severe and irreversible health effects.

What Are Heavy Metals?

Heavy metals are metallic elements with densities higher than water and with toxic effects on plants, animals, and humans.

Key characteristics:

• Non-biodegradable
• Bioaccumulative → accumulate in organism tissues
• Biomagnifying → concentration increases at higher trophic levels
• Highly toxic at low doses

Water-soluble heavy metals include:

Arsenic, Cadmium, Lead, Mercury, Barium, Chromium, Platinum, Palladium, Silver.

Among them, Arsenic, Cadmium, Lead, and Mercury are the most hazardous.

Sources of Heavy Metal Pollution

Heavy metals naturally occur in trace amounts.
But industrialisation has dramatically increased their concentrations through:
→ Metal smelting
→ Industrial emissions
→ Burning of organic waste
→ Vehicular emissions
→ Coal-based power generation

These pollutants travel long distances through wind and rain, contaminating soil and water bodies.

Heavy Metal Toxicity

Heavy metal poisoning happens when metals bind to human cells, blocking normal organ functions.

This causes:

• Irreversible organ damage
• Neurological disorders
• Developmental issues
• Cancer
• In extreme cases, death

Major Heavy Metals

Let us understand each metal with:
sources → e-waste sources → health effects → special facts

LEAD (Pb)

One of the most widely studied toxic metals.

Major Sources

• Mining
• Lead–acid batteries
• Battery recycling
• Paints & pigments
• Fly ash
• Plastic toys (lead softens PVC)

Minor Sources

• Lead-soldered food cans
• Lipsticks and cosmetics
• Water from old leaded pipes
• Glass manufacturing
• Ayurvedic medicines (due to Rasa Shastra)
• Leaded petrol (now globally phased out)

E-waste Sources

• Lead rechargeable batteries
• Solar panels
• PCBs
• CRT glass
• Lithium batteries

Health Effects

• Lung & kidney carcinogen
• Causes miscarriages & stillbirths
• Severe irreversible neurological damage in children
• Behavioral disorders, IQ decline
• Water contamination leads to cumulative poisoning
• Maternal exposure increases risk of early Alzheimer’s in offspring

Important Points

• India banned leaded petrol in 2000
• UN declared global phase-out of leaded gasoline in 2011
• Ayurvedic Rasa Shastra traditionally uses metals like lead, mercury, copper, gold, silver, tin, zinc

MERCURY (Hg)

Unique property: forms small spherical droplets due to high surface tension.

But mercury has high vapour pressure, so it evaporates rapidly, making inhalation highly dangerous.

Mercury Cycle in the Environment

• Outdoors → evaporates, enters the atmosphere
• In water → bacteria convert it into methylmercury, which is more toxic than elemental mercury

Sources

Natural:

• Volcanoes
• Metal ores
• Fossil fuels

Human-made:

• Mining & metal refining
• Coal burning
• Cement production
• Caustic soda production

E-waste:

• CFLs
• LCDs
• CRT monitors
• Switches & sensors
• Batteries
• Medical equipment
• Thermometers

Health Effects

• Permanent brain & nervous system damage
• Lung & kidney failure
• Depression, suicidal tendencies
• Paralysis
• Alzheimer’s, tremors, memory loss
• Repeated exposure severely affects children

Also: inhalation is FAR more dangerous than ingestion.

Methylmercury

Extremely toxic organometallic compound formed naturally by bacteria.

Sources:

• CFL bulbs
• Batteries
• PVC

Effects:

• Neurotoxic → damages brain & nervous system
• Causes developmental defects in fetuses

Minamata Disease (Japan, 1960s)

A tragic example of mercury poisoning.

Cause: eating fish contaminated with methylmercury from Minamata Bay.

Symptoms:

• Numbness in hands and feet
• Loss of speech, vision, hearing
• Inability to walk
• Many deaths

This led to the Minamata Convention on Mercury.

CADMIUM (Cd)

Sources

• Zinc & copper mining
• Metallurgical industries
• Electroplating

E-waste Sources

• Solar panels
• Batteries
• Solder
• PCBs
• CRT monitors
• Infrared detectors
• Semiconductor chips

Health Effects

• Liver & kidney damage
• Hypertension
• Lung cancer
• Carcinogenic

Itai-itai Disease (Japan, 1965)

• Cadmium contamination of water & rice
• Caused severe joint pain, soft bones, kidney failure
• Due to effluents from a zinc smelter

CHROMIUM (Cr)

Especially Chromium VI (Hexavalent chromium) — the most toxic form.

Sources

• Galvanising steel
• Chrome tanning (leather industry)
• Decorative chrome coating
• PVC and plastics processing

Health Effects

• DNA damage
• Liver and kidney damage
• Asthmatic bronchitis
• Lung cancer

Other Heavy Metals

Metal	Major Sources	Key Health Effects
Arsenic	• Metal ores • Fly ash • Fertiliser industries • Semiconductors • LEDs, solar cells	• Skin lesions • Cancer • Neuropathy (detailed in Water Pollution section)
Antimony	• Lead alloys (batteries) • Solder • Bearings	• Antimony trioxide: possible carcinogen
Tin	• Tin cans (food storage)	• Liver & kidney damage • Skin irritation
Zinc	• Mining • Metal smelting • Batteries • Alloys & brass • Fly ash	• Skin irritation • Pulmonary effects
Barium	• Oil & gas drilling (drilling mud) • Paint • Fireworks (green color) • Tiles • CFL bulbs • CRT front panels	• Nausea • Muscle weakness • Irregular heartbeat • Brain swelling • Paralysis
Beryllium	• Motherboards • Connectors (Cu–Be alloys)	• Lung cancer • Chronic beryllium disease • Poor wound healing