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Persistent
Organic Pollutants (POPs)
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view a printable version of this page, click here.
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Glossary
words on this page (glossary words are shown in red):
accumulate:
gather together; increase gradually
characteristics:
qualities; properties
environment:
surroundings; physical, chemical, and biological factors acting
upon an organism or an ecological community
evaporate:
change into vapor
predator:
an animal who gets most of its food by killing and eating
other animals
prey:
an animal taken by another as food
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POPs have
been called "hand-me-down poisons that threaten wildlife and people"
(World Wildlife Fund). The United Nations Environment Programme lists
twelve of them as "The Dirty Dozen." More than one hundred
of the world’s countries have been working on a treaty to ban the
production and use of these chemicals. In May 2001, diplomats from around
the world came to Stockholm, Sweden, to sign an agreement to limit POPs.
(This agreement needs to be ratified by the governments of at least
fifty countries in order to go into effect)
What
are POPs?
POPs are
chemicals that have been made by humans or result from human activity.
There are three general categories of POPs:
- Pesticides
(DDT, chlordane, heptachlor, and five others):
Produced to be toxic, in order to improve crop and livestock production
by killing agricultural pests and to kill insects carrying diseases
such as malaria and typhus
- Industrial
chemicals (PCBs and HCB):
Designed for industrial uses, such as in electrical transformers and
capacitors, in paint additives, in fireworks, ammunition, and plastics
Not intended to be toxic, but they contain harmful elements.
- By-products
of other processes (Dioxins and Furans):
Not produced intentionally; serve no useful purpose
They
occur by the burning of materials containing chlorine, such as PVC
(vinyl) plastic, bleached paper, paint strippers. They also are made
by burning municipal waste, hospital waste, hazardous waste, and by
landfill fires. They can come from power plants, diesel engines, and
other uses of leaded fuels.
Why
are people concerned about POPs?
POPs have
four main characteristics that cause worry.
-
POPs are persistent.
They are chemicals that remain in the environment
for years. In fact, they may be present for many decades. They degrade,
or break down, very slowly. Once they are produced and travel to the
air, water, soil, and food supply, POPs last a long time.
- POPs
are known to "bio-accumulate" and "bio-magnify".
POPs
have a special attraction or affinity to fats. They bind with these
fats and accumulate in the fatty tissues
of living organisms. They get into the food web as animals are eaten
by other animals. POPs become more concentrated as they move from
the bodies of smaller prey to larger
predators. The top-level predators, such
as whales, polar bears, and humans, can have higher levels of POPs
than the animals making up the basis of the food web.
- POPs
are global travelers.
POPs
move around the world by a process called "global transport".
They appear in places where they have never been used or produced.
Here’s how it works: POPs evaporate
at warm temperatures. The vapor travels in air currents of the atmosphere.
When the vapor cools, it settles on the land and water. This happens
again and again, just like a grasshopper jumps around. In fact, "the
grasshopper effect" is the name for the way POPs are able to
travel so far. POPs move thousands of miles from the warmer latitudes
of the Earth (where they are produced) to the cooler latitudes at
the North Pole and South Pole.
- POPs
are toxic.
Many
studies have shown that POPs can be harmful to wildlife and humans.
They can be dangerous at low levels as well as at high concentrations.
POPs are related to damage to the nervous system, to the liver, and
to reproduction. They are connected to birth defects. They are identified
as "endocrine-disrupters," which means they influence and
interfere with the human body’s own hormones. There may be a
connection between cancer and some POPs.
Sources:
Previous
page: The
Project
Next page: The
Ecosystem and
Food Web of the Antarctic Peninsula
Diagram
courtesy of Stockholm
Environment Institute-York; adapted from Wania, F and D. Mackay,
(1996) Tracking the distribution of persistent organic pollutants, Environ.
Sci. & Technol. 30, 390-396.
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