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Understanding Toxic Metals and Their Impact

May 14, 2025

Lecture on Toxic Metals: Arsenic, Chromium, Mercury, and Lead

Arsenic

  • Properties and Toxicity

    • Arsenic is a toxic metalloid used historically as poison ("poison of kings").
    • Causes acute death and chronic exposure can damage liver, kidneys, and lead to cancer.
    • Multi-organ toxin affecting skin (leading to skin cancer), lungs, kidneys, and nervous system.
  • Environmental Presence and Forms

    • Found naturally in rocks, soil, water, air, plants, and animals.
    • Exists in +3 (arsenic trioxide) and +5 (arsenic pentoxide) oxidation states.
    • Inorganic arsenic (bound to non-carbon elements) is more toxic than organic arsenic (bound to carbon).
  • Use and Exposure

    • Limited medicinal use; used in pesticides, taxidermy, wood preservation (e.g., Chromated Copper Arsenate - CCA).
    • Main exposure through occupational settings and contaminated water.
    • Chronic water exposure in Bangladesh led to arsenicosis.

Chromium

  • Properties and Toxicity

    • Chromium exists as essential trivalent chromium (Cr³⁺) and toxic hexavalent chromium (Cr⁶⁺).
    • Cr⁶⁺ is highly toxic, soluble, and mobile, causing oxidative damage and is a carcinogen.
  • Uses and Exposure

    • Used in industrial products: chrome plating, pigments, corrosion protection, and leather tanning.
    • Main exposure occurs via inhalation in occupational settings.

Mercury

  • Properties and Environmental Cycle

    • Mercury is unique as a liquid metal at room temperature and exists as elemental mercury (Hg⁰), inorganic mercury (Hg²⁺), and organic mercury (e.g., methylmercury).
    • Environmental mercury comes from natural sources and industrial processes.
    • Inorganic mercury can transform in the environment to more toxic organic forms.
  • Exposure and Toxicity

    • Elemental mercury vapor is highly toxic when inhaled, can cross blood-brain barrier.
    • Organic mercury from fish can cross placental barrier, affecting fetus development.

Lead

  • Properties and Usage

    • Lead is a malleable metal used for thousands of years, previously in gasoline, paints, and pipes.
    • Found in old paints, toys, candies, and some folk medicines.
  • Exposure and Toxicity

    • Absorption of lead is higher in children, leading to developmental issues.
    • Toxic to nervous system, causes reproductive harm, and crosses the placental barrier.
    • Lead poisoning in children can lead to IQ reduction, behavioral issues, and severe developmental impacts.

General Concepts

  • Mechanisms of Toxicity

    • Metals often disrupt enzyme activity, mimic essential elements (e.g., arsenic mimics phosphate), and cause oxidative damage.
  • Public Health Implications

    • Understanding metal toxicity is crucial for preventing exposure and mitigating health impacts.
    • Emphasis on studying and revisiting key concepts from this lecture for comprehensive understanding.