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Persistent organic pollutantsPersistent organic pollutants, known as POPs, are toxic substances
released into the environment by human activities. They are either used
as pesticides, consumed by industry, or generated as byproducts of various
industrial and combustion processes. These highly stable compounds can last for years or decades before
breaking down. They circulate globally through a process known as the
"grasshopper effect." POPs released in one part of the world
can, through a repeated (and often seasonal) process of evaporation
and deposit, be transported through the atmosphere to regions far away
from the original source. In addition, POPs concentrate in living organisms through another process
called bioaccumulation. Though not soluble in water, POPs are readily
absorbed in fatty tissue, where concentrations can become magnified by
up to 70 000 times the background levels. Fish, predatory birds, mammals
and humans are high up the food chain and so absorb the greatest concentrations.
When they travel, the POPs travel with them. As a result of these two
processes, POPs can be found in people and animals living in regions such
as the Arctic, thousands of kilometers from any major POPs source. Even
Brazilian pygmies deep in the Amazon have minute traces in their body
fat and higher concentrations are disrupting the breeding patterns of
seals in the Antarctic. These chemicals can also seep into the ground
water and contaminate wells and water tables. |
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