We must make a distinction between "contamination" and "pollution".
A "contaminant" is an element or compound that is "extraneous" (foreign) to the medium, (e.g. vegetable oil, salt or soil in drinking water), but not necessarily toxic or harmful per se.
A "pollutant" is an extraneous contaminant which is also one or more of the following:
- toxic (poisonous),
- teratogenic (harmful to the foetus),
- mutagenic (induces mutations in the foetus),
- pathogenic (causing disease - e.g. bacteria/virii)
- in some other way harmful to biological organisms or ecosystems (e.g. thermal pollution, compounds that use-up all the oxygen or ones that cause large increases in water turbidity and block light)
Both contaminants and pollutants can be
a) natural, or
b) anthropogenic (man-made)
They may be in their gaseous, liquid or solid "phase" and have the potential to go from one to the other, by heat changes (from to gas to liquid to solid, with a DECREASE in temperature, and viceversa) as well as evaporation, volatilisation, oxidation, precipitation.
Pollutants can be:
- assumed (biologically taken into an organism through tissues, i.e lungs, stomach, skin)
- bioaccumulated (assumed "secondhand" by eating an organism that has assumed them)
- adsorbed (stick to a surface, e.g. a pebble)
- absorbed (penetrate the tissue, e.g. a sponge)
You will find a number of lists that are internationally recognised as guides to the importance of pollutants, in terms of their effect in the EU there were a "Red List", "Black List", "Grey list" and even a "Dutch list" - considered the most advanced for its time (in the late '90s)
The US EPA I believe has its own lists but has been busy removing chemicals that make money for Bush's chronies, since he appointed an opponent of the EPA as its Head.
If this for an exam question or essay, though, be sure to revise the actual, current lists, as these frequently change and are VAST!
Commonly recognised pollutants include:
Hydrocarbons (HCs), Chlorofluorocarbons (CFCs), Chlorine, Fluorine, Boron, the Carbon monoxide (CO) and the oxides of Sulphur (SOx), Nitrogen (NOx) where x = number of oxygen atoms in the compound, PCBs, PAHs, radioactive isotopes, and many, many others.
Contrary to popular belief, neither carbon dioxide nor methane are pollutants, they are in fact contaminants, in that they exist in nature and are naturally part of the atmosphere, but in excess cause undesired effects (to humans) plants actually like CO2, they thrive on it, in fact!