This topic will provide an overview of heavy metals, including their definition, properties, sources, and common characteristics. Students will learn about the environmental and health impacts of heavy metals.
Introduction to Heavy Metals
Study guide – concise, organized, and easy to read
| Definition | Typical Characteristics |
|---|---|
| Heavy metals are metallic elements with a high atomic weight and density (generally > 5 g cm⁻³). | • Poorly biodegradable • Can exist in elemental, ionic, or compound forms • Often toxic to living organisms at low concentrations |
| Commonly referenced in environmental and health contexts. | • Frequently released by industrial activities, mining, agriculture, and combustion processes. |
Key examples
| Source Type | Typical Release Mechanism | Environmental Compartment |
|---|---|---|
| Natural | Weathering of ore deposits, volcanic eruptions | Soil, water, air |
| Industrial | Smelting, metal finishing, waste incineration | Air (particulate), effluents |
| Agricultural | Phosphate fertilizers (Cd), pesticides (As) | Soil → crops |
| Urban | Vehicle exhaust, brake wear (Pb, Cu) | Air → deposition |
| Domestic | Batteries, electronics, consumer products | Landfills → leachate |
Transport pathways
| Property | Environmental Implication |
|---|---|
| Speciation (oxidation state, complexation) | Determines mobility & toxicity (e.g., Cr(III) vs. Cr(VI)). |
| Solubility | Highly soluble ions (e.g., Pb²⁺) travel farther in water; insoluble forms may settle in sediments. |
| Adsorption | Metals bind to organic matter, clays, and oxides, influencing retention in soils. |
| Redox reactions | Reducing conditions can convert toxic species to less toxic forms (e.g., Hg⁰ volatilization). |
| pH & ionic strength | Low pH often increases metal solubility, raising bioavailability. |
| System | Typical Symptoms / Effects | Representative Metals |
|---|---|---|
| Nervous | Cognitive deficits, neuropathy, tremors | Pb, Hg |
| Renal | Kidney dysfunction, proteinuria | Cd, Hg |
| Respiratory | Pulmonary edema, bronchitis | As, Cr(VI) |
| Skeletal | Osteoporosis, bone pain | Pb, Cd |
| Carcinogenic | Lung, bladder, skin cancers | As, Cr(VI), Cd |
| Endocrine | Hormonal disruption, reproductive effects | Pb, Cd |
Mechanisms: oxidative stress, enzyme inhibition, DNA damage, disruption of ion channels, and interference with essential metal homeostasis (e.g., Fe, Zn).