Metal and Metalloid Pollution Notes

Overview

  • Metal & Metalloids; Biomagnification; Specific Metals (Lead, Arsenic, Mercury - Minamata Disease, Cadmium - Itai-itai Disease); Remediation Techniques

Metals vs. Heavy Metals

  • Metals: Heavy Metals have Specific gravity > 5. Examples: Alkali, Alkaline earth, and Transition metals.

Sources of Metals in Aquatic Systems

  • Natural: Weathering, Aeolian input, Volcanic eruptions, Sediment degradation.

  • Anthropogenic: Mining, Processing, Metal use (e.g., Pb-based paint), Sewage.

Toxicity of Metals

  • All metals are toxic at high concentrations.

  • Essential metals (Mn, Fe, Cu, Zn) can be toxic at high concentrations.

  • Non-essential metals (Hg, Cd, Pb) are toxic even at low concentrations.

  • Metal speciation is crucial to toxicity.

Metal Speciation

  • Factors: pH, O<em>2O<em>2, pE, T</em>oT</em>o, S[o/oo]S[o/oo], [Metal], [Particle], [Organic-C].

  • Forms: Dissolved vs. Particulate; Ionic; Chelated ion; Molecular; Adsorbed; Colloidal; Precipitated; Suspended; Sedimented; S-based; Methylated; Organic; Inorganic.

Redox-Controlled Metal Solubility

  • Valence change affects solubility, e.g., Fe+2(aq)→Fe+3↓+e−Fe^{+2}(aq) \rightarrow Fe^{+3} \downarrow + e^- or Mn(IV)O2↓+2e−→Mn+2(aq)Mn(IV)O_2 \downarrow + 2e^- \rightarrow Mn^{+2} (aq)

  • Oxidation state determines bioavailability and toxicity.

EPA Standards for Metals in Drinking Water

  • Lists maximum permissible contamination levels for metals like Pb, Hg, Cd, etc.

Sediment Metal Concentrations

  • Shows concentrations of Hg, As, Cu, Zn, Pb in sediments from locations like Pearl Harbor and Halifax Bay.

Biomagnification

  • Organisms biomagnify metals, leading to food chain magnification and exchange equilibrium between organism and water.

Metal Concentrations in Plankton

  • Median concentrations of metals in phytoplankton and zooplankton.

Hg Levels in a Food Chain

  • Average Hg concentration increases up the trophic levels.

Lead (Pb)

  • Widely distributed; from galena deposits; low melting point, easily extracted.

History of Pb usage

  • Used since 4000 BC; Romans used in aqueducts; Pb salts in wine caused health issues.

Pb Production & Consumption

  • Primary = mining; secondary = recycling.

  • Consumption: mainly in batteries, cable sheathing, rolled products, ammunition, pigments.

Pb in Ammunition & Gas

  • Causes waterfowl deaths; phased out in shot and gas.

Global Pb Emissions

  • Natural: Soil particles, marine aerosols, volcanoes, forest fires, biogenic processes.

  • Anthropogenic: Combustion (coal, oil, gasoline, wood), metallurgy, wood industry, garbage burning.