Environmental Engineering Reference
In-Depth Information
it is a pollutant. It could be something that occurs naturally
in the environment (e.g., metals) but is in excess, or could be
something that is man-made. Pollutants may be classified by
their origin, by their effects on organisms, by their properties
(such as toxicity), or by their persistence in the environment.
Toxic chemicals are very varied, numerous, and expensive to
monitor.
What are the major sources of pollution in the marine
environment?
Land-based sources pollute estuaries and coastal waters with
nutrients, sediments, and pathogens (disease organisms), as
well as potentially toxic chemicals including metals, pesti-
cides, industrial products, and pharmaceuticals. Following the
Industrial Revolution, more and more material has been dis-
charged from industries, sewage treatment plants, and agri-
culture, eventually reaching marine ecosystems. But pollution
does not come exclusively from land-based sources. Highly
visible events such as the Exxon Valdez oil spill in Alaska and
the Deepwater Horizon gusher in the Gulf of Mexico have pol-
luted the seas with oil from ships, and from drilling platforms
in the ocean itself. These highly publicized events have raised
public awareness of marine pollution. Other water-based
sources of pollution are less spectacular, and include dis-
charge of waste from vessels, the leaching of antifouling paints
from ships, and leaching of wood preservatives (e.g., creosote
or chromated copper arsenate) from wooden bulkheads and
dock pilings. Aquaculture operations such as floating cages in
which salmon are raised can pollute nearby waters with fish
wastes, uneaten food, antiparasite chemicals, and antibiotics.
Pollution can also enter the ocean from the atmosphere. For
example, the metal mercury is released as a gas into the atmo-
sphere from burning coal, and subsequently can be depos-
ited in the oceans. Nitrogen, in the form of nitrogen oxides
from the burning of fossil fuels, is also an air pollutant before
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