Looks at the process of bioaccumulation of synthetic chemicals and the impact of this process on the food chain.
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 Bioaccumulation is
the increase in the concentration of a chemical in a biological organism
over time. Compounds
accumulate in living things when they are absorbed and stored faster
than they are metabolized or eliminated. Understanding
bioaccumulation is important in protecting humans and other organisms
from exposure to chemicals that may cause harm. |
 One of the
first chemicals found to have harmful affects on the environment
was DDT. By the 1950s, DDT was found to be causing the decline in
bald eagle and other bird populations due to the thinning of eggshells.
In 1962, the biologist Rachel Carson, wrote about the impacts of
pesticides on wildlife and human health in her book, Silent
Spring, a landmark for the environmental movement.
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The following graphic illustrates
a typical food chain:
 Algae
is eaten by the water flea eaten by a minnow eaten by a trout and
finally
consumed by an osprey. Uptake occurs when an organism ingests a substance by breathing, swallowing, or absorbing it through the skin. Storage of a chemical in a body tissue or an organ. Bioconcentration is when there is a net accumulation of a chemical in an organism as a  result of intake and elimination. Biomagnification is
the increased accumulation in the concentration of a chemical as it
moves up through the food chain.Persistent Organic Pollutants (POPs) are synthetic chemicals that resist the normal processes of degradation. They are carbon-based chemical compounds that share four characteristics: high toxicity, persistence, fat soluble, and ability to evaporate for travelling long distances.  There are
12 top POPs (called "the Dirty Dozen" by environmental groups)
targeted by an international community of governments, scientists and
environmental groups for banning. They include: 8 pesticides (aldrin,
chlordane, DDT, dieldrin, endrin, heptachlor, mirex, and toxaphene);
2 types of industrial chemicals (polychlorinated biphenyls or PCBs
and hexachlorobenzene); and, 2 types of by-products of the manufacture,
use, and/or combustion of chlorine and chlorine-containing materials
(dioxins and furans).Banning harmful chemicals works! In 1972, DDT was banned in the  United States. Since then,
the recovery of impacted species such as the Bald eagle and the Brown
pelican have been well documented.A pesticide is any chemical used to repel, kill or control fungi, animals, or plants. Pesticides are divided into different categories depending on the kinds of organisms they are used to control. Insecticides are used to control insect populations. Fungicides are used to kill fungal growths. Mice and rats are killed by rodenticides and unwanted plants are controlled with herbicides. Since many of the POPs have been banned in the US, the chemical industry has developed new pesticides called organophosphates and carbamates. These pesticides break down into harmless products in a few hours or days so they do not  bioaccumulate.
These new pesticides do have some side effects. They are not species
specific and can kill beneficial species too. Since they do not last
long in the environment more frequent applications must be performed
which is more expensive. Also, these pesticides are much more toxic
to humans and other vertebrates. Common types of organophosphates are
malathion, parathion, and diazinon. Sevin, aldricarb and propoxur are
examples of carbamates. In order to eliminate the use of synthetic chemicals, some farmers are returning to the traditional methods of farming now called "organic farming." While they do experience smaller yields than farms that use synthetic chemicals, on an average, organic farms use only 40% of the energy used on conventional farms. This reduces costs and raises the profit margin. |
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| In order to
eliminate the use of synthetic
 chemicals, some farmers are returning
to the traditional methods of farming now called "organic farming." While
they do experience smaller yields than farms that use synthetic chemicals,
on an average, organic farms use only 40% of the energy used on conventional
farms. This reduces costs and raises the profit margin. |
Vocabulary: uptake storage bioconcentration biomagnification POPs pesticide fungicides rodenticides herbicides organophosphates carbamates organic toxicity  |
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