HEAVY METALS

What's the definition of heavy metal

Any metallic chemical element that has a huge specific gravity & high relative atomic mass.

What is the Threshold Limit Value (TLV) and Time Weighted Average (TWA) for Mercury ?

1. Elemental and inorganic : 0.025mg/m3

2. Alkyl mercury : 0.01mg/m3

3. Mercury vapor : 0.05mg/m3

What are the forms of Hg ?

1. Elemental (Hg0) / hydragyrum : liquid at room °C

2. Inorganic (Hg+1) / mercurous / mercuric

3. Organic mercury (CH3Hg+) : most toxic

What is the MOA of mercury ?

Reacts with sulfhydryl (SH) group, causing enzyme inhibition and pathologic alteration of cellular membrane.

Which mercury are toxic to CNS and a pulmonary irritant ?

Elemental and methylmercury : toxic to CNS

Metallic mercury vapor : pulmonary irritant

What is the main target organ for inorganic mercury toxicity?

Kidney (nephrotoxicant; affects proximal tubules)

How does mercury cause nephrotoxicity?

Binds to sulfhydryl (SH) groups of membrane proteins → damages proximal tubule cells

Which mercury compound can cross the blood-brain barrier?

Organic mercury (methylmercury)

What neurological symptoms are seen in mercury poisoning?

Tremors, irritability, shyness, insomnia, nervousness, dementia

What disease resulted from mercury pollution in Japan?

Minamata Disease

Explain "biomagnification" in mercury toxicity.

Mercury accumulates in aquatic organisms and increases in concentration up the food chain.

Why are heavy metals dangerous even at low levels?

They are persistent and bioaccumulate in living organisms, causing chronic toxicity

How can inorganic mercury still affect the CNS long-term?

It can convert into organic forms that cross the BBB.

Which mercury compound is possibly carcinogenic to humans?

Methylmercury (Group 2B, IARC)

Describe the cause of Minamata disease.

Industrial discharge of mercury → bacterial conversion to methylmercury → contaminated fish → neurotoxicity in humans.

What is the TLV-TWA for inorganic and tetraethyl lead?

Inorganic Pb = 0.05 mg/m³, Tetraethyl Pb = 0.10 mg/m³

Which population absorbs more lead?

Children (70% absorption vs. 20% in adults)

Why are children more vulnerable to lead poisoning?

Developing nervous system + higher calcium demand (lead mimics calcium)

What is the first symptom of lead poisoning in children?

Blood lead level (BLL) ≥ 10 µg/dL

Name two enzymes inhibited by lead in heme synthesis

δ-ALA dehydratase, ferrochelatase

What are two biochemical markers of lead poisoning?

↑ ALA in urine, ↑ protoporphyrin IX in blood

Name 3 classic signs of lead poisoning (plumbism).

Burton's line, basophilic stippling of RBCs, wrist drop

What are some complications of lead toxicity?

Anemia, encephalopathy, renal tubular acidosis, peripheral neuropathy, intestinal colic

What effect does lead have on the CNS of children?

Reduced IQ, poor memory, behavioral problems

Renal effect of chronic lead poisoning?

Tubular acidosis (Fanconi's syndrome)

What is basophilic stippling?

Aggregation of ribosomal RNA in red cells — characteristic of lead toxicity.

Which form of arsenic is more toxic: organic or inorganic?

Inorganic (As³⁺ > As⁵⁺)

What is the TLV for arsine gas?

0.05 ppm

What is the mechanism of acute arsenic toxicity?

As³⁺ binds sulfhydryl groups → inhibits mitochondrial enzymes → ↓ ATP production

What are acute arsenic poisoning symptoms?

Abdominal pain, vomiting, bloody diarrhea, collapse, death (12-48 hr)

What are chronic arsenic toxicity features?

Skin hyperpigmentation, palmar-plantar hyperkeratosis, garlic odor, Mee's lines, peripheral neuropathy

What disease is associated with chronic arsenic exposure?

"Blackfoot disease" (peripheral vascular disease)

What cancers are linked to arsenic exposure?

Skin, lung, bladder (possibly kidney, liver, prostate)

Which is more toxic: organic or inorganic arsenic?

Inorganic (especially As³⁺)

Which foods are high in inorganic arsenic?

Grains (rice, barley, oats)

Which foods contain more organic arsenic?

Fruits, vegetables, shrimp

Onset of acute arsenic poisoning symptoms?

Within 1 hour of ingestion

Mechanism of acute As toxicity?

As³⁺ binds to sulfhydryl groups → inhibits mitochondrial enzymes → ↓ ATP

Mechanism of chronic As toxicity?

Long-term inhibition of enzymatic systems + oxidative stress + DNA damage

What are the dermatologic signs of chronic arsenic toxicity?

Hyperpigmentation and palmar-plantar hyperkeratosis

What is "Blackfoot disease"?

Peripheral vascular disease from chronic arsenic exposure

What are "Mee's lines"?

White transverse lines on nails — seen in arsenic poisoning

What cancers are caused by arsenic?

Skin, lung, bladder; possibly kidney, liver, prostate

What odor is characteristic of arsenic poisoning?

Garlic odor on breath

What classification did IARC assign to arsenic?

Group 1 — Known human carcinogen

What is the TLV-TWA for cadmium?

5 µg/m³

What Japanese disease is caused by cadmium toxicity?

Itai-Itai disease

What are the main clinical features of Itai-Itai disease?

Osteomalacia, osteoporosis, severe bone pain, renal failure

What organ stores most cadmium in the body?

Kidneys (50–75% as Cd–metallothionein complex)

What is the half-life of cadmium in the body?

20–30 years

Why is cadmium considered a cumulative nephrotoxicant?

It is reabsorbed and retained in proximal tubule cells for decades.

Pulmonary effects of cadmium exposure?

Pulmonary edema, emphysema, pneumonitis, bronchopneumonia

What percentage of lung cancers may be linked to cadmium exposure?

~8%

What are cadmium’s effects on the lungs?

Pulmonary edema, emphysema, bronchopneumonia, lung cancer risk

Name two tell-tale signs of chronic arsenic poisoning.

Mee’s lines, palmar-plantar hyperkeratosis

The Itai-Itai disease was one of four major pollution cases in Japan. Name the other three.

Minamata disease (Hg), Niigata-Minamata disease (Hg), Yokkaichi asthma (air pollution)

Which heavy metals are primarily nephrotoxic?

Mercury (inorganic) and cadmium

Which heavy metals are primarily neurotoxic?

Mercury (organic) and lead

Which heavy metals are known carcinogens?

Arsenic (Group 1), Cadmium (probable), Methylmercury (Group 2B)

Which two metals bind to sulfhydryl (–SH) groups?

Mercury and arsenic