Pollutants: Fate, Behavior and Transport in the Environment
A pollutant is defined as any physical, chemical, biological, or
radiological substance or matter that has an adverse effect on air,
water, or soil. In this page, an attempt has been made to discuss
the various sources of the pollutants, exposure pathways, and to list the various pollutants category-wise and also media-wise.
Environmental contaminants are potentially harmful agents that
have been released into the ecosystem and have entered our food,
water, air, or soil.
Some substances that degrade slowly and remain in the environment
for a long time are called persistent contaminants. When
contaminants are released into the environment, their persistence
becomes an important concern.
A substance that is relatively toxic may be a minor hazard if it
breaks down quickly into non hazardous substances before people
can be exposed to it. Conversely, a mildly toxic contaminant that
remains for a long time in environmental media to which humans are
exposed can accumulate in human tissues and become a significant
Elements such as lead or cadmium do not break down. Some organic
chemicals such as DDT, dioxins and furans, and polychlorinated biphenyls
break down very slowly in the environment and in human tissue even
though they can be destroyed under extreme conditions, i.e., high
Pollutants can enter the environment in many different ways. Most
of the contaminants can be found in multiple media. For example,
benzene from a gasoline spill initially contaminates the soil. Some
from the initial contamination evaporates into the air, while the
rest pollutes the groundwater.
The sources of pollutants can be categorized into two types: Point
Sources and Non-point sources. Point sources of contaminants are
localized and are often easily identified. Such point sources can
- industrial discharges
- waste incinerators.
- sewage treatment plants
- waste disposal sites.
Non-point sources of contaminants are also important. These sources
are more diffuse and not as easily identified as point sources are.
They can include:
- run off from land that has been treated with pesticides or fertilizers
- car exhausts
- storm-water run off from built-up areas
- atmospheric deposition, which is the transfer of contaminants
out of the atmosphere onto the land and into the water. For example,
metals or organic chemicals on dust particles can fall on water.
Often these contaminants have travelled long distances and reacted
with other chemicals in the air (e.g., acid rain).
It is important, though, to note the difference between exposure
and pollution. Not all pollution leads to exposure. The following
figure shows that person A is being exposed to the contamination
in multiple pathways (air and groundwater), while person B is not
being exposed in spite of being near the area of pollution.
Click here for information
on different exposure pathways
Click here for information
on contaminants in water, air and soil.