According to Marietta College 2006, not only DDT is toxin to biomagnify, but also all of the following have the potential to biomagnify Table 1.
Table 1. List of Chemical which has Potential to Biomagnify.
Substance Use and Problems
Links
PCBs polychlorinated biphenyls
•
insulators in transformers
•
plasticizer
•
fire retardant
•
biomagnifies
•
impairs reproduction
•
widespread in aquatic systems
•
as airborne contaminants
•
in sediments
•
in the Mississippi River
PAHs polynuclear aromatic
hydrocarbons
•
component of petroleum products
•
carcinogenic Heavy metals:
•
mercury
•
copper
•
cadmium
•
chromium
•
lead
•
nickel
•
zinc
•
tin TBT or tributyltin
•
mercury from gold mining
•
many from metal processing
•
may affect nervous system
•
may affect reproduction
•
from an interesting student project
•
heavy metals in the Mississippi River
- great source
cyanide
•
used in leaching gold
•
used in fishing
•
toxic
•
effects on coral reefs
•
health information
•
proposed gold mine
and its effects
•
report of a spill
of cyanide selenium
•
concentrated by farming desert soils
•
reproductive failures
•
toxic
•
selenium at a wildlife
refuge in Wyoming
Source: http:www.marietta.edu~biol1022bioma95.html
C. Properties of Biomagnification Chemicals
In order for biomagnification to occur, the pollutant must be: 1 long-lived, 2 mobile, 3 soluble in fats, and 4 biologically active. If a pollutant is short-lived,
it will be broken down before it can become dangerous. If it is not mobile, it will stay in one place and is unlikely to be taken up by organisms. If the pollutant is
soluble in water it will be excreted by the organism. Pollutants that dissolve in fats, however, may be retained for a long time. It is traditional to measure the
amount of pollutants in fatty tissues of organisms such as fish. In mammals, we often test the milk produced by females, since the milk has a lot of fat in it and
because the very young are often more susceptible to damage from toxins
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poisons. If a pollutant is not active biologically, it may biomagnify, but we really dont worry about it much, since it probably wont cause any problems Marietta
College, 2006.
D. Case Examples of Biomagnification 1. Biomagnification was caused by DDT
The best example of biomagnification comes from DDT. DDT stands for dichloro diphenyl trichloroethane. It is a chlorinated hydrocarbon, a class of
chemicals which often fit the characteristics necessary for biomagnification. This long-lived pesticide insecticide has improved human health in many countries
by killing insects such as mosquitoes that spread disease. On the other hand, DDT is effective in part because it does not break down in the environment. It is
picked up by organisms in the environment and incorporated into fat. Even here, it does no real damage in many organisms including humans. In others,
however, DDT is deadly or may have more insidious, long-term effects. In birds, for instance, DDT interferes with the deposition of calcium in the shells of the
birds eggs. The eggs laid are very soft and easily broken; birds so afflicted are rarely able to raise young and this causes a decline in their numbers.
This was so apparent in the early 1960s that it led the scientist Rachel Carson to postulate a silent spring without the sound of bird calls. Her book
Silent Spring led to the banning of DDT, the search for pesticides that would not biomagnify, and the birth of the modern environmental movement in the 1960s.
Birds such as the bald eagle have made comebacks in response to the banning of DDT in the US. Ironically, many of the pesticides which replaced DDT are
more dangerous to humans, and, without DDT, disease primarily in the tropics claims more human lives.
The above studies refer to aquatic systems. In terrestrial systems, direct uptake by higher trophic levels must be much less, occurring via the lungs. This
critique of the biomagnification concept does not mean that we need not be concerned about synthetic organic contaminants and metal elements because
they will become diluted. Bioaccumulation and bioconcentration result in these substances remaining in the organisms and not being diluted to non-threatening
concentrations. The success of top predatory-bird recovery bald eagles, peregrine falcons in North America following the ban on DDT use in agriculture
is testamnet to the importance of biomagnification Marietta College, 2006.
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DDT has a half-life of 15 years, which means if you use 100 kg of DDT, it will break down as follows Table 2:
Table 2. A half-life of 15 years using 100 kg of DDT Year
Amount Remaining
100 kg 15
50 kg 30
25 kg 45
12.5 kg 60
6.25 kg 75
3.13 kg 90
1.56 kg 105
0.78 kg 120
0.39 kg This means that after 100 years, there will still be over a pound of DDT in
the environment. If it does bioaccumulate and biomagnify, much of the DDT will be in the bodies of organisms. DDT actually has rather low toxicity to humans
but high toxicity to insects, hence its use as an insecticide. Because it could be safely handled by humans, it was extensively used shortly after its discovery just
before WW II. During the war, it was used to reduce mosquito populations and thus control malaria in areas where US troops were fighting particularly in the
tropics. It was also used on civilian populations in Europe, to prevent the spread of lice and the diseases they carried. Refugee populations and those living in
destroyed cities would have otherwise faced epidemics of louse-born diseases. After the war, DDT became popular not only to protect humans from insect-
borne diseases, but to protect crops as well. As the first of the modern pesticides, it was overused, and soon led to the discovery of the phenomena of
insect resistance to pesticides, bioaccumulation, and biomagnification Marietta College, 2006.
By the 1960s, global problems with DDT and other pesticides were becoming so pervasive that they began to attract much attention. Credit for
sounding the warning about DDT and biomagnification usually goes to the scientist Rachel Carson, who wrote the influential book Silent Spring 1962. The
silent spring alluded to in the title describes a world in which all the songbirds have been poisoned. Her book of course was attacked by many with vested
interests.
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B. Biomagnification was caused by Mercury
