PRINCIPLES OF ENVIRONMENTAL TOXICOLOGY AND CONTAMINATION (PART I)

Table of Contents

1. Index
2. UNIT 1 - General principles
3. UNIT 2 - Main sources of environmental contamination
4. UNIT 3 - Air Pollution
   1. Types of air pollutants
   2. Sources of air pollutants
   3. Examples of air pollutants and their human health effects
   4. Air pollutants and Environmental Effects
   5. Summarizing...
5. Unit 4 - Water and soil Pollution
6. Glossary of key terms associated with environmental toxicology

Types of air pollutants

Air pollutants can be divided into:

Gaseous pollutants - These substances are gases at normal temperature and pressure as well as vapours evaporated from substances that are solid or liquid. Among gaseous pollutants of greatest concern are hydrocarbons, hydrogen sulphide (H₂S), carbon monoxide (CO), nitrogen oxides (N_xO_y), ozone (O₃), and other oxidants, sulphur oxides (S_xO_y), and CO2. Other common gaseous pollutants are hydrogen cyanide and ammonia gas.

Particulate pollutants - Fine solids or liquid droplets that can be suspended in the air. Some of the different types of particulates are defined as follows:

1. Dust - Relatively large solid particles about 100 µm in diameter that come directly from the substances being used (e.g. sawdust, ash, cement dust, grain dust, coal dust).

2. Fumes - Suspended solids less than 1 µm in diameter usually released from metallurgical or chemical processes (e.g. zinc and lead oxides).

3. Mist - Liquid droplets suspended in the air with a diameter less than 2.0 µm (e.g. sulphuric acid mist).

4. Smoke - Solid particles (0.05 - 1.0 µm) resulting from incomplete combustion of fossil fuels.

5. Aerosol - Solid or liquid particles (< 1.0 µm) suspended in the air or another gas.

Suspensions classified as liquids also include fogs (small particles). Fogs and mists (large particles) are produced from condensation, atomization, or entrapment of liquids by gases.

In order to affect the biota, particulate pollutants must be in a size range that allows them to enter the organism and remain there; that is, they must be in an aerosol or on solid particles small enough to possess a low settling velocity.